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2020-04-05T04:43:48Z
User contributions
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https://scioly.org/wiki/index.php?title=User:Voltage&diff=31511
User:Voltage
2014-05-19T19:06:11Z
<p>Voltage: /* Competition */</p>
<hr />
<div>Hi. I'm from [[Pilgrimage Homeschool]] Division B.<br />
<br />
Thanks for checking out my user page.<br />
<br />
Voltage's Avatar:<br />
<br />
[[File:Voltage's Avatar 1.jpeg]]<br />
<br />
==Competition==<br />
<br />
''Note: AA means placing in AA league. OV means placing overall. AA/OV means I don't know.''<br />
<br />
{|class = "wikitable"<br />
|+2012-2013<br />
!Event<br />
!Regional<br />
!State<br />
|-<br />
|Disease Detectives<br />
|2nd AA/OV<br />
|2nd AA/OV<br />
|-<br />
|Road Scholar<br />
|1st AA/OV<br />
|1st AA/OV<br />
|-<br />
|Experimental Design<br />
|2nd AA/OV<br />
|1st AA/OV<br />
|-<br />
|}<br />
<br />
{|class = "wikitable"<br />
|+2013-2014<br />
!Event<br />
!Regional<br />
!State<br />
!National<br />
|-<br />
|Disease Detectives<br />
|3rd AA, 4th OV<br />
|1st OV<br />
|7th OV<br />
|-<br />
|Road Scholar<br />
|1st OV<br />
|1st OV<br />
|35th OV<br />
|-<br />
|Experimental Design<br />
|1st OV<br />
|1st OV<br />
|9th OV<br />
|-<br />
|Simple Machines<br />
|1st OV<br />
|1st OV<br />
|18th OV<br />
|-<br />
|Shock Value<br />
|1st OV<br />
|1st OV<br />
|4th OV<br />
|-<br />
|Metric Mastery<br />
|4th AA, 7th OV<br />
|1st OV<br />
|25th OV<br />
|-<br />
|}<br />
<br />
[[Category:User Pages]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30864
Chemistry Lab/Electrochemistry
2014-04-15T22:48:27Z
<p>Voltage: /* Electrolytic Cells */ Adding some electroplating info</p>
<hr />
<div>This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
[[File:Voltaic Cell Porous Barrier.png]]<br />
<br />
A porous barrier allows ions to flow from the anode compartment to the cathode compartment and vice versa, balancing the charge. The electrode compartments are called '''half-cells'''.<br />
<br />
Salt bridges may be used as an alternative to porous barriers.<br />
<br />
[[File:Voltaic Cell Salt Bridge.jpeg]]<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
One principle use of electrolytic cells is to electroplate objects such as nails and silverware.<br />
<br />
'''Coulombs''' is a measure of charge. '''Current''' is a measure of the flow of electrons. The SI unit of current is the ampere, expressed as C/s or coulombs per second.<br />
<br />
Coulombs = amperes <math>\times</math> seconds<br />
<br />
Given the current run through an electrolytic cell and the time it is run, you can calculate the number of coulombs. There are 1.602E-19 coulombs in an electron. From the amount of coulombs you may calculate the number of electrons used to reduce.<br />
<br />
Say that you are electroplating copper onto a plate.<br />
<br />
<math>Cu^{2+} + 2e^- \to Cu</math><br />
<br />
Given the number of electrons used to reduce the copper ions, you may calculate the amount of Cu electroplated onto the plate. This is applicable to any electroplating situation.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Electromotive Force (emf)==<br />
<br />
The '''emf''' of a cell, measured in volts, is the potential difference between the cathode and the anode of a cell. It tells you how much potential there is to do work. Electromotive means "causing electron motion".<br />
<br />
===Measuring emf===<br />
<br />
It is quite easy to measure emf. Take a voltmeter and touch the probes to the cathode and anode. The voltmeter will tell you what the voltage difference, or emf, is.<br />
<br />
===Standard Reduction (Half-Cell) Potentials===<br />
<br />
'''Reduction Potentials''' tell you how much something "wants" to reduce. For example, <math>Cu^{2+}</math> (with a reduction reaction of <math>Cu^{2+} + 2e^- \to Cu</math>) has a higher reduction potential then <math>Fe^{2+}</math> (with a reduction reaction of <math>Fe^{2+} + 2e^- \to Fe</math>). This means that <math>Cu^{2+}</math> "wants" to reduce more then <math>Fe^{2+}</math>.<br />
<br />
Like all potentials, reduction potentials are not absolute and have to be with respect to something.<br />
<br />
'''Standard Reduction Potentials''', denoted <math>E_{red}^{\circ}</math> are the reduction potential with respect to a reference reaction. This reference reaction is the reduction of <math>H^+</math>.<br />
<br />
<math>2H^+ + 2e^- \to H_2</math><br />
<br />
An electrode designed to produce this half reaction is called a '''standard hydrogen electrode''' (SHE) or the '''normal hydrogen electrode''' (NHE). A SHE consists of a piece of platinum foil covered with finely divided platinum. The electrode is encased in a glass tube so that hydrogen gas at STP can bubble over the platinum. (STP refers to 273 Kelvin and 1 atm) The solution contains <math>H^+</math>.<br />
<br />
[[File:SHE.gif]]<br />
<br />
Here is a table of standard reduction potentials:<br />
<br />
{|class = "wikitable"<br />
|+Standard Reduction Potentials in Water at 25 <math>^{\circ}</math>C<br />
!Reduction Half-Reaction<br />
!Potential(V)<br />
|-<br />
!<math>F_2 + 2e^- \to 2F^-</math><br />
!+2.87<br />
|-<br />
!<math>MnO_4^- + 8H^+ + 5e^- \to Mn^2+ + 4H_2O</math><br />
!+1.51<br />
|-<br />
!<math>Cl_2 + 2e^- \to 2Cl^-</math><br />
!+1.36<br />
|-<br />
!<math>Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O</math><br />
!+1.33<br />
|-<br />
!<math>O_2 + 4H^+ + 4e^- \to 2H_2O</math><br />
!+1.23<br />
|-<br />
!<math>Br_2 + 2e^- \to 2Br^-</math><br />
!+1.06<br />
|-<br />
!<math>NO_3^- + 4H^+ + 3e^- \to NO + 2H_2O</math><br />
!+0.96<br />
|-<br />
!<math>Ag^+ + e^- \to Ag</math><br />
!+0.80<br />
|-<br />
!<math>Fe^{3+} + e^- \to Fe^{2+}</math><br />
!+0.77<br />
|-<br />
!<math>O_2 + 2H^+ + 2e^- \to H_2O_2</math><br />
!+0.68<br />
|-<br />
!<math>MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-</math><br />
!+0.59<br />
|-<br />
!<math>I_2 + 2e^- \to 2I^-</math><br />
!+0.54<br />
|-<br />
!<math>O_2 + 2H_2O + 4e^- \to 4OH^-</math><br />
!+0.40<br />
|-<br />
!<math>Cu^{2+} + 2e^- \to Cu</math><br />
!+0.34<br />
|-<br />
!<math>2H^+ + 2e^- \to H_2</math><br />
!0[defined]<br />
|-<br />
!<math>Ni^{2+} + 2e^- \to Ni</math><br />
!-0.28<br />
|-<br />
!<math>Fe^{2+} + 2e^- \to Fe</math><br />
!-0.44<br />
|-<br />
!<math>Zn^{2+} + 2e^- \to Zn</math><br />
!-0.76<br />
|-<br />
!<math>2H_2O + 2e^- \to H_2 + 2OH^-</math><br />
!-0.83<br />
|-<br />
!<math>Al^{3+} + 3e^- \to Al</math><br />
!-1.66<br />
|-<br />
!<math>Na^+ + e^- \to Na</math><br />
!-2.71<br />
|-<br />
!<math>Li^+ + e^- \to Li</math><br />
!-3.05<br />
|-<br />
|}<br />
Table from "The Central Science".<br />
<br />
===Calculating emf===<br />
<br />
To calculate the emf of a cell, simply take the standard reduction potential of the cathode and subtract the standard reduction potential of the anode from it. Because electron potential measures potential energy per charge, the stoichiometric coefficients in the half-reactions do not affect the value of the standard reduction potential or the emf of the cell.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30863
Chemistry Lab/Electrochemistry
2014-04-15T22:41:24Z
<p>Voltage: /* Electrolytic Cells */</p>
<hr />
<div>This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
[[File:Voltaic Cell Porous Barrier.png]]<br />
<br />
A porous barrier allows ions to flow from the anode compartment to the cathode compartment and vice versa, balancing the charge. The electrode compartments are called '''half-cells'''.<br />
<br />
Salt bridges may be used as an alternative to porous barriers.<br />
<br />
[[File:Voltaic Cell Salt Bridge.jpeg]]<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
One principle use of electrolytic cells is to electroplate objects such as nails and silverware.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Electromotive Force (emf)==<br />
<br />
The '''emf''' of a cell, measured in volts, is the potential difference between the cathode and the anode of a cell. It tells you how much potential there is to do work. Electromotive means "causing electron motion".<br />
<br />
===Measuring emf===<br />
<br />
It is quite easy to measure emf. Take a voltmeter and touch the probes to the cathode and anode. The voltmeter will tell you what the voltage difference, or emf, is.<br />
<br />
===Standard Reduction (Half-Cell) Potentials===<br />
<br />
'''Reduction Potentials''' tell you how much something "wants" to reduce. For example, <math>Cu^{2+}</math> (with a reduction reaction of <math>Cu^{2+} + 2e^- \to Cu</math>) has a higher reduction potential then <math>Fe^{2+}</math> (with a reduction reaction of <math>Fe^{2+} + 2e^- \to Fe</math>). This means that <math>Cu^{2+}</math> "wants" to reduce more then <math>Fe^{2+}</math>.<br />
<br />
Like all potentials, reduction potentials are not absolute and have to be with respect to something.<br />
<br />
'''Standard Reduction Potentials''', denoted <math>E_{red}^{\circ}</math> are the reduction potential with respect to a reference reaction. This reference reaction is the reduction of <math>H^+</math>.<br />
<br />
<math>2H^+ + 2e^- \to H_2</math><br />
<br />
An electrode designed to produce this half reaction is called a '''standard hydrogen electrode''' (SHE) or the '''normal hydrogen electrode''' (NHE). A SHE consists of a piece of platinum foil covered with finely divided platinum. The electrode is encased in a glass tube so that hydrogen gas at STP can bubble over the platinum. (STP refers to 273 Kelvin and 1 atm) The solution contains <math>H^+</math>.<br />
<br />
[[File:SHE.gif]]<br />
<br />
Here is a table of standard reduction potentials:<br />
<br />
{|class = "wikitable"<br />
|+Standard Reduction Potentials in Water at 25 <math>^{\circ}</math>C<br />
!Reduction Half-Reaction<br />
!Potential(V)<br />
|-<br />
!<math>F_2 + 2e^- \to 2F^-</math><br />
!+2.87<br />
|-<br />
!<math>MnO_4^- + 8H^+ + 5e^- \to Mn^2+ + 4H_2O</math><br />
!+1.51<br />
|-<br />
!<math>Cl_2 + 2e^- \to 2Cl^-</math><br />
!+1.36<br />
|-<br />
!<math>Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O</math><br />
!+1.33<br />
|-<br />
!<math>O_2 + 4H^+ + 4e^- \to 2H_2O</math><br />
!+1.23<br />
|-<br />
!<math>Br_2 + 2e^- \to 2Br^-</math><br />
!+1.06<br />
|-<br />
!<math>NO_3^- + 4H^+ + 3e^- \to NO + 2H_2O</math><br />
!+0.96<br />
|-<br />
!<math>Ag^+ + e^- \to Ag</math><br />
!+0.80<br />
|-<br />
!<math>Fe^{3+} + e^- \to Fe^{2+}</math><br />
!+0.77<br />
|-<br />
!<math>O_2 + 2H^+ + 2e^- \to H_2O_2</math><br />
!+0.68<br />
|-<br />
!<math>MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-</math><br />
!+0.59<br />
|-<br />
!<math>I_2 + 2e^- \to 2I^-</math><br />
!+0.54<br />
|-<br />
!<math>O_2 + 2H_2O + 4e^- \to 4OH^-</math><br />
!+0.40<br />
|-<br />
!<math>Cu^{2+} + 2e^- \to Cu</math><br />
!+0.34<br />
|-<br />
!<math>2H^+ + 2e^- \to H_2</math><br />
!0[defined]<br />
|-<br />
!<math>Ni^{2+} + 2e^- \to Ni</math><br />
!-0.28<br />
|-<br />
!<math>Fe^{2+} + 2e^- \to Fe</math><br />
!-0.44<br />
|-<br />
!<math>Zn^{2+} + 2e^- \to Zn</math><br />
!-0.76<br />
|-<br />
!<math>2H_2O + 2e^- \to H_2 + 2OH^-</math><br />
!-0.83<br />
|-<br />
!<math>Al^{3+} + 3e^- \to Al</math><br />
!-1.66<br />
|-<br />
!<math>Na^+ + e^- \to Na</math><br />
!-2.71<br />
|-<br />
!<math>Li^+ + e^- \to Li</math><br />
!-3.05<br />
|-<br />
|}<br />
Table from "The Central Science".<br />
<br />
===Calculating emf===<br />
<br />
To calculate the emf of a cell, simply take the standard reduction potential of the cathode and subtract the standard reduction potential of the anode from it. Because electron potential measures potential energy per charge, the stoichiometric coefficients in the half-reactions do not affect the value of the standard reduction potential or the emf of the cell.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=User:Voltage&diff=30821
User:Voltage
2014-04-14T16:37:56Z
<p>Voltage: /* My Events */</p>
<hr />
<div>Hi. I'm from [[Pilgrimage Homeschool]] Division B.<br />
<br />
Thanks for checking out my user page.<br />
<br />
Voltage's Avatar:<br />
<br />
[[File:Voltage's Avatar 1.jpeg]]<br />
<br />
==Competition==<br />
<br />
''Note: AA means placing in AA league. OV means placing overall. AA/OV means I don't know.''<br />
<br />
{|class = "wikitable"<br />
|+2012-2013<br />
!Event<br />
!Regional<br />
!State<br />
|-<br />
|Disease Detectives<br />
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{|class = "wikitable"<br />
|+2013-2014<br />
!Event<br />
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|Disease Detectives<br />
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[[Category:User Pages]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Acids_and_Bases&diff=30753
Chemistry Lab/Acids and Bases
2014-04-13T12:39:05Z
<p>Voltage: /* Equilibrium Constants */</p>
<hr />
<div>This page refers to the [[2009]] focus of [[Chem Lab]].<br />
==Acids and Bases (2009)==<br />
Acids and Bases is basically an acid/base titration lab. Be sure you know what a titration is, because it is not a good thing if you do not. This is a fairly quick and simple lab to complete, and it is more than worthwhile to double check your lab if you have enough materials. More repetitions of the lab can result in a more accurate answer. In a free-response style lab report, this might also get you some extra points for style and accuracy. Acid/base questions can range in difficulty from identifying if a solution was an acid based on its pH to balancing advanced reactions trying to find the acidic constant. In order to excel in this event you must be prepared for all levels.<br />
<br />
==Solutions==<br />
<br />
For more info on solutions see [[Chem Lab/Aqueous Solutions]]<br />
<br />
==pH and pOH==<br />
<br />
pH + pOH = 14<br />
<br />
===pH===<br />
<br />
pH is equal to the <math>-\log [H^+]</math> or <math>-\log [H_3O^+]</math>.<br />
<br />
===pOH===<br />
<br />
pOH is equal to the <math>-\log[OH^-]</math>.<br />
<br />
==Acids==<br />
<br />
All acids have a pH less than 7<br />
<br />
===Arrhenius Acids===<br />
<br />
Arrhenius Acids are defined to be chemicals that, when put in water, produce hydronium (<math>H_3O^+</math>) ions.<br />
<br />
===Bronsted-Lowry Acids===<br />
<br />
Bronsted-Lowry Acids are defined to be chemicals that donate protons (<math>H^+</math>). This is a broader definition than the Arrhenius definition because it does not have to involve water.<br />
<br />
===Lewis Acids===<br />
<br />
Lewis Acids are defined to be chemicals that accept electron pairs.<br />
<br />
===Strong Acids===<br />
<br />
Strong Acids are acids that pretty much completely disassociate in water. Some examples of Strong Acids are: <math>HI, HBr, HClO_4, HCl, HClO_3, H_2SO_4</math>, and <math>HNO_3 </math><br />
<br />
===Weak Acids===<br />
<br />
Weak Acids are acids that only partially disassociate in water. They have a Ka to define how much. Weak Acids consist of pretty much everything that is not a strong acid. For example: <math>HCOOH, CH_3COOH, HOOCCHOHCHOHCOOH,</math> and <math>{HSO_4}^-</math><br />
<br />
==Bases==<br />
<br />
All bases have a pH greater than 7.<br />
<br />
===Arrhenius Bases===<br />
<br />
Arrhenius Bases are defined to be chemicals that, when put in water, produce hydroxide (<math>OH^-</math>) ions.<br />
<br />
===Bronsted-Lowry Bases===<br />
<br />
Bronsted Lowry Acids are defined to be chemical that accept protons (<math>H^+</math>). This is a broader definition than the Arrhenius definition because it does not have to involve water.<br />
<br />
===Lewis Bases===<br />
<br />
Lewis Bases are defined to be chemicals that donate electron pairs.<br />
<br />
===Strong Bases===<br />
<br />
Strong Bases are bases that pretty much completely disassociate in water. Examples include <math>LiOH, NaOH, KOH, RbOH,</math> and <math>CsOH</math>.<br />
<br />
===Weak Bases===<br />
<br />
Weak Bases are bases that only partially disassociate in water. They have a Kb to define how much. A common example of a weak base is <math>NH_3</math>.<br />
<br />
==Equilibrium Constants==<br />
<br />
Take this reaction:<br />
<br />
<math>aA + bB \to cC + dD </math><br />
<br />
The equilibrium constant is equal to:<br />
<br />
<math>k=\frac{[C]^c * [D]^d}{[A]^a * [B]^b}</math><br />
<br />
Where all of the concentrations are the concentrations at equilibrium and where solids are excluded.<br />
<br />
For more info on equilibrium, see [[Chem Lab/Equilibrium]].<br />
<br />
===Acid Dissociation Constant===<br />
<br />
The acid equilibrium constant (Ka) is equal to<br />
<br />
<math>\frac{[H^+][A^-]}{[HA]}</math><br />
<br />
for the following reaction:<br />
<br />
<math>HA \to H^+ + A^-</math><br />
<br />
===Base Dissociation Constant===<br />
<br />
The base dissociation constant (Kb) is equal to<br />
<br />
<math>\frac{[BH^+][OH^-]}{[B]}</math><br />
<br />
for the following reaction:<br />
<br />
<math>B + H_2O \to BH^+ + OH^-</math><br />
<br />
===Dissociation Constant of Water===<br />
<br />
The dissociation constant of water (Kw) is equal to<br />
<br />
<math>[H^+][OH^-] = 1*10^{-14}</math><br />
<br />
for the following reaction:<br />
<br />
<math>H_2O \to H^+ + OH^-</math><br />
<br />
This is why pH + pOH = 14<br />
<br />
===Relationship between Ka and Kb===<br />
<br />
<math>\frac{[H^+][NH_3]}{[NH_4^+]} * \frac{[NH_4^+][OH^-]}{[NH_3]} = [H^+][OH^-]</math><br />
<br />
This method works for all acids and bases. Thus,<br />
<br />
Ka <math>*</math> Kb = Kw<br />
<br />
==Titrations==<br />
<br />
For more info on Titrations, see [[Chem Lab/Titration Race]].<br />
<br />
===Links===<br />
*Acid and base links [http://users.erols.com/merosen/acidbase.htm]<br />
<br />
[[Category:Chem Lab]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30724
Chemistry Lab/Electrochemistry
2014-04-12T15:25:22Z
<p>Voltage: </p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
[[File:Voltaic Cell Porous Barrier.png]]<br />
<br />
A porous barrier allows ions to flow from the anode compartment to the cathode compartment and vice versa, balancing the charge. The electrode compartments are called '''half-cells'''.<br />
<br />
Salt bridges may be used as an alternative to porous barriers.<br />
<br />
[[File:Voltaic Cell Salt Bridge.jpeg]]<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Electromotive Force (emf)==<br />
<br />
The '''emf''' of a cell, measured in volts, is the potential difference between the cathode and the anode of a cell. It tells you how much potential there is to do work. Electromotive means "causing electron motion".<br />
<br />
===Measuring emf===<br />
<br />
It is quite easy to measure emf. Take a voltmeter and touch the probes to the cathode and anode. The voltmeter will tell you what the voltage difference, or emf, is.<br />
<br />
===Standard Reduction (Half-Cell) Potentials===<br />
<br />
'''Reduction Potentials''' tell you how much something "wants" to reduce. For example, <math>Cu^{2+}</math> (with a reduction reaction of <math>Cu^{2+} + 2e^- \to Cu</math>) has a higher reduction potential then <math>Fe^{2+}</math> (with a reduction reaction of <math>Fe^{2+} + 2e^- \to Fe</math>). This means that <math>Cu^{2+}</math> "wants" to reduce more then <math>Fe^{2+}</math>.<br />
<br />
Like all potentials, reduction potentials are not absolute and have to be with respect to something.<br />
<br />
'''Standard Reduction Potentials''', denoted <math>E_{red}^{\circ}</math> are the reduction potential with respect to a reference reaction. This reference reaction is the reduction of <math>H^+</math>.<br />
<br />
<math>2H^+ + 2e^- \to H_2</math><br />
<br />
An electrode designed to produce this half reaction is called a '''standard hydrogen electrode''' (SHE) or the '''normal hydrogen electrode''' (NHE). A SHE consists of a piece of platinum foil covered with finely divided platinum. The electrode is encased in a glass tube so that hydrogen gas at STP can bubble over the platinum. (STP refers to 273 Kelvin and 1 atm) The solution contains <math>H^+</math>.<br />
<br />
[[File:SHE.gif]]<br />
<br />
Here is a table of standard reduction potentials:<br />
<br />
{|class = "wikitable"<br />
|+Standard Reduction Potentials in Water at 25 <math>^{\circ}</math>C<br />
!Reduction Half-Reaction<br />
!Potential(V)<br />
|-<br />
!<math>F_2 + 2e^- \to 2F^-</math><br />
!+2.87<br />
|-<br />
!<math>MnO_4^- + 8H^+ + 5e^- \to Mn^2+ + 4H_2O</math><br />
!+1.51<br />
|-<br />
!<math>Cl_2 + 2e^- \to 2Cl^-</math><br />
!+1.36<br />
|-<br />
!<math>Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O</math><br />
!+1.33<br />
|-<br />
!<math>O_2 + 4H^+ + 4e^- \to 2H_2O</math><br />
!+1.23<br />
|-<br />
!<math>Br_2 + 2e^- \to 2Br^-</math><br />
!+1.06<br />
|-<br />
!<math>NO_3^- + 4H^+ + 3e^- \to NO + 2H_2O</math><br />
!+0.96<br />
|-<br />
!<math>Ag^+ + e^- \to Ag</math><br />
!+0.80<br />
|-<br />
!<math>Fe^{3+} + e^- \to Fe^{2+}</math><br />
!+0.77<br />
|-<br />
!<math>O_2 + 2H^+ + 2e^- \to H_2O_2</math><br />
!+0.68<br />
|-<br />
!<math>MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-</math><br />
!+0.59<br />
|-<br />
!<math>I_2 + 2e^- \to 2I^-</math><br />
!+0.54<br />
|-<br />
!<math>O_2 + 2H_2O + 4e^- \to 4OH^-</math><br />
!+0.40<br />
|-<br />
!<math>Cu^{2+} + 2e^- \to Cu</math><br />
!+0.34<br />
|-<br />
!<math>2H^+ + 2e^- \to H_2</math><br />
!0[defined]<br />
|-<br />
!<math>Ni^{2+} + 2e^- \to Ni</math><br />
!-0.28<br />
|-<br />
!<math>Fe^{2+} + 2e^- \to Fe</math><br />
!-0.44<br />
|-<br />
!<math>Zn^{2+} + 2e^- \to Zn</math><br />
!-0.76<br />
|-<br />
!<math>2H_2O + 2e^- \to H_2 + 2OH^-</math><br />
!-0.83<br />
|-<br />
!<math>Al^{3+} + 3e^- \to Al</math><br />
!-1.66<br />
|-<br />
!<math>Na^+ + e^- \to Na</math><br />
!-2.71<br />
|-<br />
!<math>Li^+ + e^- \to Li</math><br />
!-3.05<br />
|-<br />
|}<br />
Table from "The Central Science".<br />
<br />
===Calculating emf===<br />
<br />
To calculate the emf of a cell, simply take the standard reduction potential of the cathode and subtract the standard reduction potential of the anode from it. Because electron potential measures potential energy per charge, the stoichiometric coefficients in the half-reactions do not affect the value of the standard reduction potential or the emf of the cell.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30722
Chemistry Lab/Electrochemistry
2014-04-12T13:46:06Z
<p>Voltage: /* Voltaic Cells */</p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
[[File:Voltaic Cell Porous Barrier.png]]<br />
<br />
A porous barrier allows ions to flow from the anode compartment to the cathode compartment and vice versa, balancing the charge. The electrode compartments are called '''half-cells'''.<br />
<br />
Salt bridges may be used as an alternative to porous barriers.<br />
<br />
[[File:Voltaic Cell Salt Bridge.jpeg]]<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Electromotive Force (emf)==<br />
<br />
The '''emf''' of a cell, measured in volts, is the potential difference between the cathode and the anode of a cell. It tells you how much potential there is to do work. Electromotive means "causing electron motion".<br />
<br />
===Measuring emf===<br />
<br />
It is quite easy to measure emf. Take a voltmeter and touch the probes to the cathode and anode. The voltmeter will tell you what the voltage difference, or emf, is.<br />
<br />
===Standard Reduction (Half-Cell) Potentials===<br />
<br />
'''Reduction Potentials''' tell you how much something "wants" to reduce. For example, <math>Cu^{2+}</math> (with a reduction reaction of <math>Cu^{2+} + 2e^- \to Cu</math>) has a higher reduction potential then <math>Fe^{2+}</math> (with a reduction reaction of <math>Fe^{2+} + 2e^- \to Fe</math>). This means that <math>Cu^{2+}</math> "wants" to reduce more then <math>Fe^{2+}</math>.<br />
<br />
Like all potentials, reduction potentials are not absolute and have to be with respect to something.<br />
<br />
'''Standard Reduction Potentials''', denoted <math>E_{red}^{\circ}</math> are the reduction potential with respect to a reference reaction. This reference reaction is the reduction of <math>H^+</math>.<br />
<br />
<math>2H^+ + 2e^- \to H_2</math><br />
<br />
An electrode designed to produce this half reaction is called a '''standard hydrogen electrode''' (SHE) or the '''normal hydrogen electrode''' (NHE). A SHE has as its anode a piece of platinum foil covered with finely divided platinum. The electrode is encased in a glass tube so that hydrogen gas at STP can bubble over the platinum. (STP refers to 273 Kelvin and 1 atm) The solution contains <math>H^+</math>.<br />
<br />
[[File:SHE.gif]]<br />
<br />
Here is a table of standard reduction potentials:<br />
<br />
{|class = "wikitable"<br />
|+Standard Reduction Potentials in Water at 25 <math>^{\circ}</math>C<br />
!Reduction Half-Reaction<br />
!Potential(V)<br />
|-<br />
!<math>F_2 + 2e^- \to 2F^-</math><br />
!+2.87<br />
|-<br />
!<math>MnO_4^- + 8H^+ + 5e^- \to Mn^2+ + 4H_2O</math><br />
!+1.51<br />
|-<br />
!<math>Cl_2 + 2e^- \to 2Cl^-</math><br />
!+1.36<br />
|-<br />
!<math>Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O</math><br />
!+1.33<br />
|-<br />
!<math>O_2 + 4H^+ + 4e^- \to 2H_2O</math><br />
!+1.23<br />
|-<br />
!<math>Br_2 + 2e^- \to 2Br^-</math><br />
!+1.06<br />
|-<br />
!<math>NO_3^- + 4H^+ + 3e^- \to NO + 2H_2O</math><br />
!+0.96<br />
|-<br />
!<math>Ag^+ + e^- \to Ag</math><br />
!+0.80<br />
|-<br />
!<math>Fe^{3+} + e^- \to Fe^{2+}</math><br />
!+0.77<br />
|-<br />
!<math>O_2 + 2H^+ + 2e^- \to H_2O_2</math><br />
!+0.68<br />
|-<br />
!<math>MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-</math><br />
!+0.59<br />
|-<br />
!<math>I_2 + 2e^- \to 2I^-</math><br />
!+0.54<br />
|-<br />
!<math>O_2 + 2H_2O + 4e^- \to 4OH^-</math><br />
!+0.40<br />
|-<br />
!<math>Cu^{2+} + 2e^- \to Cu</math><br />
!+0.34<br />
|-<br />
!<math>2H^+ + 2e^- \to H_2</math><br />
!0[defined]<br />
|-<br />
!<math>Ni^{2+} + 2e^- \to Ni</math><br />
!-0.28<br />
|-<br />
!<math>Fe^{2+} + 2e^- \to Fe</math><br />
!-0.44<br />
|-<br />
!<math>Zn^{2+} + 2e^- \to Zn</math><br />
!-0.76<br />
|-<br />
!<math>2H_2O + 2e^- \to H_2 + 2OH^-</math><br />
!-0.83<br />
|-<br />
!<math>Al^{3+} + 3e^- \to Al</math><br />
!-1.66<br />
|-<br />
!<math>Na^+ + e^- \to Na</math><br />
!-2.71<br />
|-<br />
!<math>Li^+ + e^- \to Li</math><br />
!-3.05<br />
|-<br />
|}<br />
Table from "The Central Science".<br />
<br />
===Calculating emf===<br />
<br />
To calculate the emf of a cell, simply take the standard reduction potential of the cathode and subtract the standard reduction potential of the anode from it. Because electron potential measures potential energy per charge, the stoichiometric coefficients in the half-reactions do not affect the value of the standard reduction potential or the emf of the cell.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30721
Chemistry Lab/Electrochemistry
2014-04-12T13:43:58Z
<p>Voltage: /* Voltaic Cells */</p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
[[File:Voltaic Cell Porous Barrier.png]]<br />
<br />
A porous barrier allows ions to flow from the anode compartment to the cathode compartment and vice versa, balancing the charge. The electrode compartments are called '''half-cells'''.<br />
<br />
Salt bridges may be used as an alternative to porous barriers.<br />
<br />
[[File:Voltaic Cell Salt Bridge,jpeg]]<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Electromotive Force (emf)==<br />
<br />
The '''emf''' of a cell, measured in volts, is the potential difference between the cathode and the anode of a cell. It tells you how much potential there is to do work. Electromotive means "causing electron motion".<br />
<br />
===Measuring emf===<br />
<br />
It is quite easy to measure emf. Take a voltmeter and touch the probes to the cathode and anode. The voltmeter will tell you what the voltage difference, or emf, is.<br />
<br />
===Standard Reduction (Half-Cell) Potentials===<br />
<br />
'''Reduction Potentials''' tell you how much something "wants" to reduce. For example, <math>Cu^{2+}</math> (with a reduction reaction of <math>Cu^{2+} + 2e^- \to Cu</math>) has a higher reduction potential then <math>Fe^{2+}</math> (with a reduction reaction of <math>Fe^{2+} + 2e^- \to Fe</math>). This means that <math>Cu^{2+}</math> "wants" to reduce more then <math>Fe^{2+}</math>.<br />
<br />
Like all potentials, reduction potentials are not absolute and have to be with respect to something.<br />
<br />
'''Standard Reduction Potentials''', denoted <math>E_{red}^{\circ}</math> are the reduction potential with respect to a reference reaction. This reference reaction is the reduction of <math>H^+</math>.<br />
<br />
<math>2H^+ + 2e^- \to H_2</math><br />
<br />
An electrode designed to produce this half reaction is called a '''standard hydrogen electrode''' (SHE) or the '''normal hydrogen electrode''' (NHE). A SHE has as its anode a piece of platinum foil covered with finely divided platinum. The electrode is encased in a glass tube so that hydrogen gas at STP can bubble over the platinum. (STP refers to 273 Kelvin and 1 atm) The solution contains <math>H^+</math>.<br />
<br />
[[File:SHE.gif]]<br />
<br />
Here is a table of standard reduction potentials:<br />
<br />
{|class = "wikitable"<br />
|+Standard Reduction Potentials in Water at 25 <math>^{\circ}</math>C<br />
!Reduction Half-Reaction<br />
!Potential(V)<br />
|-<br />
!<math>F_2 + 2e^- \to 2F^-</math><br />
!+2.87<br />
|-<br />
!<math>MnO_4^- + 8H^+ + 5e^- \to Mn^2+ + 4H_2O</math><br />
!+1.51<br />
|-<br />
!<math>Cl_2 + 2e^- \to 2Cl^-</math><br />
!+1.36<br />
|-<br />
!<math>Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O</math><br />
!+1.33<br />
|-<br />
!<math>O_2 + 4H^+ + 4e^- \to 2H_2O</math><br />
!+1.23<br />
|-<br />
!<math>Br_2 + 2e^- \to 2Br^-</math><br />
!+1.06<br />
|-<br />
!<math>NO_3^- + 4H^+ + 3e^- \to NO + 2H_2O</math><br />
!+0.96<br />
|-<br />
!<math>Ag^+ + e^- \to Ag</math><br />
!+0.80<br />
|-<br />
!<math>Fe^{3+} + e^- \to Fe^{2+}</math><br />
!+0.77<br />
|-<br />
!<math>O_2 + 2H^+ + 2e^- \to H_2O_2</math><br />
!+0.68<br />
|-<br />
!<math>MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-</math><br />
!+0.59<br />
|-<br />
!<math>I_2 + 2e^- \to 2I^-</math><br />
!+0.54<br />
|-<br />
!<math>O_2 + 2H_2O + 4e^- \to 4OH^-</math><br />
!+0.40<br />
|-<br />
!<math>Cu^{2+} + 2e^- \to Cu</math><br />
!+0.34<br />
|-<br />
!<math>2H^+ + 2e^- \to H_2</math><br />
!0[defined]<br />
|-<br />
!<math>Ni^{2+} + 2e^- \to Ni</math><br />
!-0.28<br />
|-<br />
!<math>Fe^{2+} + 2e^- \to Fe</math><br />
!-0.44<br />
|-<br />
!<math>Zn^{2+} + 2e^- \to Zn</math><br />
!-0.76<br />
|-<br />
!<math>2H_2O + 2e^- \to H_2 + 2OH^-</math><br />
!-0.83<br />
|-<br />
!<math>Al^{3+} + 3e^- \to Al</math><br />
!-1.66<br />
|-<br />
!<math>Na^+ + e^- \to Na</math><br />
!-2.71<br />
|-<br />
!<math>Li^+ + e^- \to Li</math><br />
!-3.05<br />
|-<br />
|}<br />
Table from "The Central Science".<br />
<br />
===Calculating emf===<br />
<br />
To calculate the emf of a cell, simply take the standard reduction potential of the cathode and subtract the standard reduction potential of the anode from it. Because electron potential measures potential energy per charge, the stoichiometric coefficients in the half-reactions do not affect the value of the standard reduction potential or the emf of the cell.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=File:Voltaic_Cell_Salt_Bridge.jpeg&diff=30720
File:Voltaic Cell Salt Bridge.jpeg
2014-04-12T13:43:19Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30719
Chemistry Lab/Electrochemistry
2014-04-12T13:41:04Z
<p>Voltage: </p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
[[File:Voltaic Cell Porous Barrier.png]]<br />
<br />
A porous barrier allows ions to flow from the anode compartment to the cathode compartment and vice versa, balancing the charge. The electrode compartments are called '''half-cells'''.<br />
<br />
Salt bridges may be used as an alternative to porous barriers.<br />
<br />
[[File:Voltaic Cell Salt Bridge,png]]<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Electromotive Force (emf)==<br />
<br />
The '''emf''' of a cell, measured in volts, is the potential difference between the cathode and the anode of a cell. It tells you how much potential there is to do work. Electromotive means "causing electron motion".<br />
<br />
===Measuring emf===<br />
<br />
It is quite easy to measure emf. Take a voltmeter and touch the probes to the cathode and anode. The voltmeter will tell you what the voltage difference, or emf, is.<br />
<br />
===Standard Reduction (Half-Cell) Potentials===<br />
<br />
'''Reduction Potentials''' tell you how much something "wants" to reduce. For example, <math>Cu^{2+}</math> (with a reduction reaction of <math>Cu^{2+} + 2e^- \to Cu</math>) has a higher reduction potential then <math>Fe^{2+}</math> (with a reduction reaction of <math>Fe^{2+} + 2e^- \to Fe</math>). This means that <math>Cu^{2+}</math> "wants" to reduce more then <math>Fe^{2+}</math>.<br />
<br />
Like all potentials, reduction potentials are not absolute and have to be with respect to something.<br />
<br />
'''Standard Reduction Potentials''', denoted <math>E_{red}^{\circ}</math> are the reduction potential with respect to a reference reaction. This reference reaction is the reduction of <math>H^+</math>.<br />
<br />
<math>2H^+ + 2e^- \to H_2</math><br />
<br />
An electrode designed to produce this half reaction is called a '''standard hydrogen electrode''' (SHE) or the '''normal hydrogen electrode''' (NHE). A SHE has as its anode a piece of platinum foil covered with finely divided platinum. The electrode is encased in a glass tube so that hydrogen gas at STP can bubble over the platinum. (STP refers to 273 Kelvin and 1 atm) The solution contains <math>H^+</math>.<br />
<br />
[[File:SHE.gif]]<br />
<br />
Here is a table of standard reduction potentials:<br />
<br />
{|class = "wikitable"<br />
|+Standard Reduction Potentials in Water at 25 <math>^{\circ}</math>C<br />
!Reduction Half-Reaction<br />
!Potential(V)<br />
|-<br />
!<math>F_2 + 2e^- \to 2F^-</math><br />
!+2.87<br />
|-<br />
!<math>MnO_4^- + 8H^+ + 5e^- \to Mn^2+ + 4H_2O</math><br />
!+1.51<br />
|-<br />
!<math>Cl_2 + 2e^- \to 2Cl^-</math><br />
!+1.36<br />
|-<br />
!<math>Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O</math><br />
!+1.33<br />
|-<br />
!<math>O_2 + 4H^+ + 4e^- \to 2H_2O</math><br />
!+1.23<br />
|-<br />
!<math>Br_2 + 2e^- \to 2Br^-</math><br />
!+1.06<br />
|-<br />
!<math>NO_3^- + 4H^+ + 3e^- \to NO + 2H_2O</math><br />
!+0.96<br />
|-<br />
!<math>Ag^+ + e^- \to Ag</math><br />
!+0.80<br />
|-<br />
!<math>Fe^{3+} + e^- \to Fe^{2+}</math><br />
!+0.77<br />
|-<br />
!<math>O_2 + 2H^+ + 2e^- \to H_2O_2</math><br />
!+0.68<br />
|-<br />
!<math>MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-</math><br />
!+0.59<br />
|-<br />
!<math>I_2 + 2e^- \to 2I^-</math><br />
!+0.54<br />
|-<br />
!<math>O_2 + 2H_2O + 4e^- \to 4OH^-</math><br />
!+0.40<br />
|-<br />
!<math>Cu^{2+} + 2e^- \to Cu</math><br />
!+0.34<br />
|-<br />
!<math>2H^+ + 2e^- \to H_2</math><br />
!0[defined]<br />
|-<br />
!<math>Ni^{2+} + 2e^- \to Ni</math><br />
!-0.28<br />
|-<br />
!<math>Fe^{2+} + 2e^- \to Fe</math><br />
!-0.44<br />
|-<br />
!<math>Zn^{2+} + 2e^- \to Zn</math><br />
!-0.76<br />
|-<br />
!<math>2H_2O + 2e^- \to H_2 + 2OH^-</math><br />
!-0.83<br />
|-<br />
!<math>Al^{3+} + 3e^- \to Al</math><br />
!-1.66<br />
|-<br />
!<math>Na^+ + e^- \to Na</math><br />
!-2.71<br />
|-<br />
!<math>Li^+ + e^- \to Li</math><br />
!-3.05<br />
|-<br />
|}<br />
Table from "The Central Science".<br />
<br />
===Calculating emf===<br />
<br />
To calculate the emf of a cell, simply take the standard reduction potential of the cathode and subtract the standard reduction potential of the anode from it. Because electron potential measures potential energy per charge, the stoichiometric coefficients in the half-reactions do not affect the value of the standard reduction potential or the emf of the cell.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=File:SHE.gif&diff=30718
File:SHE.gif
2014-04-12T13:39:18Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:Voltaic_Cell_Porous_Barrier.png&diff=30717
File:Voltaic Cell Porous Barrier.png
2014-04-12T13:25:27Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30716
Chemistry Lab/Electrochemistry
2014-04-12T13:24:57Z
<p>Voltage: </p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
[[File:Voltaic Cell Porous Barrier.png]]<br />
<br />
A porous barrier allows ions to flow from the anode compartment to the cathode compartment and vice versa, balancing the charge. The electrode compartments are called '''half-cells'''.<br />
<br />
Salt bridges may be used as an alternative to porous barriers.<br />
<br />
[[File:Voltaic Cell Salt Bridge,png]]<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Electromotive Force (emf)==<br />
<br />
The '''emf''' of a cell, measured in volts, is the potential difference between the cathode and the anode of a cell. It tells you how much potential there is to do work. Electromotive means "causing electron motion".<br />
<br />
===Measuring emf===<br />
<br />
It is quite easy to measure emf. Take a voltmeter and touch the probes to the cathode and anode. The voltmeter will tell you what the voltage difference, or emf, is.<br />
<br />
===Standard Reduction (Half-Cell) Potentials===<br />
<br />
'''Reduction Potentials''' tell you how much something "wants" to reduce. For example, <math>Cu^{2+}</math> (with a reduction reaction of <math>Cu^{2+} + 2e^- \to Cu</math>) has a higher reduction potential then <math>Fe^{2+}</math> (with a reduction reaction of <math>Fe^{2+} + 2e^- \to Fe</math>). This means that <math>Cu^{2+}</math> "wants" to reduce more then <math>Fe^{2+}</math>.<br />
<br />
Like all potentials, reduction potentials are not absolute and have to be with respect to something.<br />
<br />
'''Standard Reduction Potentials''', denoted <math>E_{red}^{\circ}</math> are the reduction potential with respect to a reference reaction. This reference reaction is the reduction of <math>H^+</math>.<br />
<br />
<math>2H^+ + 2e^- \to H_2</math><br />
<br />
An electrode designed to produce this half reaction is called a '''standard hydrogen electrode''' (SHE) or the '''normal hydrogen electrode''' (NHE). A SHE has as its anode a piece of platinum foil covered with finely divided platinum. The electrode is encased in a glass tube so that hydrogen gas at STP can bubble over the platinum. (STP refers to 273 Kelvin and 1 atm) The solution contains <math>H^+</math>.<br />
<br />
[[File:Standard Hydrogen Electrode.gif]]<br />
<br />
Here is a table of standard reduction potentials:<br />
<br />
{|class = "wikitable"<br />
|+Standard Reduction Potentials in Water at 25 <math>^{\circ}</math>C<br />
!Reduction Half-Reaction<br />
!Potential(V)<br />
|-<br />
!<math>F_2 + 2e^- \to 2F^-</math><br />
!+2.87<br />
|-<br />
!<math>MnO_4^- + 8H^+ + 5e^- \to Mn^2+ + 4H_2O</math><br />
!+1.51<br />
|-<br />
!<math>Cl_2 + 2e^- \to 2Cl^-</math><br />
!+1.36<br />
|-<br />
!<math>Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O</math><br />
!+1.33<br />
|-<br />
!<math>O_2 + 4H^+ + 4e^- \to 2H_2O</math><br />
!+1.23<br />
|-<br />
!<math>Br_2 + 2e^- \to 2Br^-</math><br />
!+1.06<br />
|-<br />
!<math>NO_3^- + 4H^+ + 3e^- \to NO + 2H_2O</math><br />
!+0.96<br />
|-<br />
!<math>Ag^+ + e^- \to Ag</math><br />
!+0.80<br />
|-<br />
!<math>Fe^{3+} + e^- \to Fe^{2+}</math><br />
!+0.77<br />
|-<br />
!<math>O_2 + 2H^+ + 2e^- \to H_2O_2</math><br />
!+0.68<br />
|-<br />
!<math>MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-</math><br />
!+0.59<br />
|-<br />
!<math>I_2 + 2e^- \to 2I^-</math><br />
!+0.54<br />
|-<br />
!<math>O_2 + 2H_2O + 4e^- \to 4OH^-</math><br />
!+0.40<br />
|-<br />
!<math>Cu^{2+} + 2e^- \to Cu</math><br />
!+0.34<br />
|-<br />
!<math>2H^+ + 2e^- \to H_2</math><br />
!0[defined]<br />
|-<br />
!<math>Ni^{2+} + 2e^- \to Ni</math><br />
!-0.28<br />
|-<br />
!<math>Fe^{2+} + 2e^- \to Fe</math><br />
!-0.44<br />
|-<br />
!<math>Zn^{2+} + 2e^- \to Zn</math><br />
!-0.76<br />
|-<br />
!<math>2H_2O + 2e^- \to H_2 + 2OH^-</math><br />
!-0.83<br />
|-<br />
!<math>Al^{3+} + 3e^- \to Al</math><br />
!-1.66<br />
|-<br />
!<math>Na^+ + e^- \to Na</math><br />
!-2.71<br />
|-<br />
!<math>Li^+ + e^- \to Li</math><br />
!-3.05<br />
|-<br />
|}<br />
Table from "The Central Science".<br />
<br />
===Calculating emf===<br />
<br />
To calculate the emf of a cell, simply take the standard reduction potential of the cathode and subtract the standard reduction potential of the anode from it. Because electron potential measures potential energy per charge, the stoichiometric coefficients in the half-reactions do not affect the value of the standard reduction potential or the emf of the cell.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=File:XNOR_rect_logic_gate.png&diff=30710
File:XNOR rect logic gate.png
2014-04-11T23:33:16Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:XOR_rect_logic_gate.png&diff=30709
File:XOR rect logic gate.png
2014-04-11T23:32:54Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:NOR_rect_logic_gate.png&diff=30708
File:NOR rect logic gate.png
2014-04-11T23:32:32Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:NAND_rect_logic_gate.png&diff=30707
File:NAND rect logic gate.png
2014-04-11T23:32:15Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:NOT_rect_logic_gate.png&diff=30706
File:NOT rect logic gate.png
2014-04-11T23:31:54Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:OR_rect_logic_gate.png&diff=30705
File:OR rect logic gate.png
2014-04-11T23:31:31Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=Circuit_Lab&diff=30704
Circuit Lab
2014-04-11T23:30:59Z
<p>Voltage: /* Digital Logic */ More images</p>
<hr />
<div>{{EventLinksBox<br />
|active=yes<br />
|type=Physics<br />
|cat=Lab<br />
|2009thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=17&t=403 2009]<br />
|2010tests=[http://scioly.org/wiki/2009_Test_Exchange#Shock_Value 2010]<br />
|2010thread=[http://scioly.org/phpBB3/viewtopic.php?f=65&t=1278 2010]<br />
|2011thread=[http://scioly.org/phpBB3/viewtopic.php?f=92&t=2222 2011]<br />
|2011tests=2011<br />
|2013thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=142&t=3691 2013]<br />
|2013tests=2013<br />
|2014thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=166&t=4951 2014]<br />
|2014tests=2014<br />
|2014questions=[http://www.scioly.org/phpBB3/viewtopic.php?f=173&t=5022 2014]<br />
|B Champion=[[Daniel Wright Junior High School]]<br />
|C Champion=[[Harriton High School]]<br />
}}<br />
==Introduction==<br />
Circuit Lab is a laboratory event which deals with the various components and properties of direct current (DC) circuits. Historically, the fields which have been tested in this event are DC circuit concepts and DC circuit analysis (both theory and practice).<br />
<br />
==What is a Circuit?==<br />
Let's take an example of a battery, for now. The battery has a positive (+) end, and a minus ( - ) end. When you touch a wire onto both ends of the battery at the same time, you have created a circuit. (It is generally ill advised to attempt this experiment. Not only will there be nothing to see, but short-circuiting a battery is potentially dangerous). What just happened? Current flowed from one end of the battery to the other through your wire. Therefore, our definition of circuit can simply be a never-ending looped pathway for electrons (the battery counts as a pathway!).<br />
<br />
'''The Requirement of a Closed Conducting Path'''<br />
<br />
There are two requirements which must be met to establish an electric circuit. The first is clearly demonstrated by the above activity. There must be a closed conducting path which extends from the positive terminal to the negative terminal. It is not enough that there is a closed connecting loop; the loop itself must extend from the positive terminal to the negative terminal of the electrochemical cell. An electric circuit is like a water circuit at a water park. The flow of charge through the wires is similar to the flow of water through the pipes and along the slides of the water park. If a pipe gets plugged or broken such that water cannot make a complete path through the circuit, then the flow of water will soon cease. In an electric circuit, all connections must be made and made by conducting materials capable of carrying charge. Metallic materials are conductors and can be inserted into the circuit to successfully light the bulb. There must be a closed conducting loop from the positive to the negative terminal in order to establish a circuit and to have a current.<br />
<br />
==Basic Electrical DC Circuit Theory==<br />
===Current Flow and Direction===<br />
'''"Conventional Current Flow" vs. "Electron Flow"''' - This has to do with how circuit diagrams are interpreted. Now, remember we said that electrons are 'flowing' in the wires? The question here deals with : Do they 'flow' from the positive end of the battery, or the negative end of the battery?<br />
<br />
Just as where in mathematics subtracting a negative is equivalent to adding a negative, so also a flow of positive charges in one direction is the exact same current as a flow of negative charges in the opposite direction. As such in most applications, the choice of current direction is an arbitrary convention.<br />
<br />
Conventional current flow, devised by Benjamin Franklin, views the current as a "flow" of positive charges. Therefore, this concept holds that current "flows" out of the positive end of the battery. Electron flow, on the other hand, deals with the ACTUAL route of the electrons (the primary carrier of electric charge in most circuits). Being negatively charged particles, electron currents moves out of the negative end of the battery.<br />
<br />
===Current===<br />
<br />
What is an "electron?" To put it simply, an electron is an atomic particle which carries a negative charge. These electrons spin around the nucleus of an atom, which has a positive charge, and is located in the very center of the atom. The concept of "electricity" has to do with these electrons and with their "electron flow." Do you remember the example of our battery? This battery takes these negatively charged electrons from a chemical reaction inside the battery, pushes them out of the negative end of the battery, and into the wire. These electrons will then bump electrons in the atoms of the wire over and over until finally electrons arrive back at the positive end of the battery. Elements which allow this process of "bumping" those electrons on over determines how conductive the element is. So, when there's a current, it's just electrons bumping each other from atom to atom and flowing on. The individual electrons generally move very slowly, but the electric current moves at the speed of light.<br />
<br />
<br />
A circuit requires a loop for the electrons to travel on (think of "circle"). This means you can not simply attach a wire to one end of a battery and expect electrons to flow through it. As stated before, in our definition of the circuit, a continuous loop is required. But think about it scientifically: If you did attach the wire to only one end of the battery, where would the electrons go that got bumped to the opposite end of the wire? That is why there needs to be that continuous loop of wire: the electrons need somewhere to go.<br />
<br />
==Voltage, Resistance, and Amperes==<br />
<br />
''For more in-depth information, see [[Circuit Lab (Episodes)|Episode 1]]''<br />
<br />
===Amperes(Symbol I or rarely A)=== <br />
To consider Amps pretend that you are the coach of a baseball team. You want to make your team the best that it can be. There are two ways you can do this, making your team score as much as possible and making the opposing team score as little as possible. Focusing on both would be impossible so naturally you're going to have to choose one area to focus on: say you want to score more runs; let's relate this to the concept of "amperes." The amount of runs you make is your score - the more you get the better your chance of winning. Similarly, amperes measure the amount of current you have flowing per second through an area: is it a lot, or a little bit? Now, if you want to win the game, you don't necessarily have to score a whole lot of runs, you just need to score more than your opponent. So, maybe your resistance to their scoring of runs will be high - and resistance to current flowing is also one of our important terms we need to know. Now, how do these concepts of amperes and resistance relate, straying from the daemons for now? If you multiply the resistance by the amperes, you have the voltage of a circuit (remember, we're always talking about in circuits here, not on a baseball field). This relationship was discovered by Georg Simon Ohm, and it says, simply, that: <br />
<br />
<math>V = I \times R</math> <br />
<br />
Or <br />
<br />
Voltage = Current times Resistance <br />
<br />
*Sometimes E is used in place of V, for electromotive force(EMF), it's the same thing, don't worry.<br />
<br />
[[File:Cool Story.png]]<br />
<br />
===Voltage(V or sometimes E)===<br />
Imagine a battery as a super-soaker, and the water that comes out of it as voltage. The harder you pump that super-soaker, the harder that stream is going to be when it comes out of the gun. Voltage is the potential for that water to go very quickly out of the gun: the more you pumped, putting more "voltage" in, the faster that water will go: but sometimes you will have a "multi-functioning" nozzle which even allows you to adjust that water speed even further. You want the water to go out in a "wider" and "bigger" stream, you might change the nozzle to a bigger opening. What you've just done is changed the amount of space that the water is allowed to go through: the water is now given a much bigger space to flow through. The "voltage," or potential, of the water to go fast and give bruises is still high, but now you've taken away from its hitting-power by spreading it out. Anyone know where I'm going next with this? The bigger your nozzle gets (think of it like the resistance), the smaller the hitting power (current (which is a speed in electricity too!)) is going to be.<br />
<br />
Voltage is technically electrical potential. While in many cases we treat it as an absolute, it is important to remember that in circuits we talk mostly about the difference in voltage, a potential difference, and that things like Ohm's laws only apply to potential ''differences'' not just electrical potential. However, in the context of circuits, Voltage is often used in reference to potential difference.<br />
<br />
=== Resistance(Î©)=== <br />
<br />
A resistor is just a piece of metal, and the piece in the center there is what provides the resistance.<br />
<br />
And as for what resistance is itself - it is the force against the flow of the electrons. They transform the electrical energy they absorb into heat energy.<br />
<br />
Imagine our electrons - flowing along the wire, pushing new electrons to flow on, and so on. This wire is not very hard to flow in - it's made of a material that's very conductive. But what would happen if we placed something in the middle of the wire that was harder for the electrons to flow through? They're going to be bumping into all the atoms in the material, which will cause the atoms to vibrate. This, in turn, will cause nearby air molecules to take some energy. That energy is in the form of heat. Where did it come from again? From the electrons bumping into atoms inside the resistor. <br />
<br />
===Other Analogy===<br />
The other way that these three are explained is using water as an example. Imagine the basic components of a circuit, a battery, wire, and say, a resistor. In the water analogy, this translates to a pump(because the battery pushes electrons around the circuit), some large pipe(wire), and a section of much smaller pipe(resistor). We know that in the water analogy, the flow rate of the pump is the same as the voltage of the battery, and the pressure in the tubing if the same as the current in the circuit. This is a pretty simple way to explain voltage/current/ and resistance. If we up the voltage, but keep the resistance(pipe size) the same, it logically takes more pressure, however if we keep the flow rate the same and put in large pipes, it takes a lot less pressure to so the same job. Conversely, if we drop the pressure, but keep the same pipe size, the flow rate goes down, and if we maintain constant pressure, but increase the pipe size, the flow rate goes up. And that's all there is to it. Thus we can see the relationships in Ohm's law. Here a fancy picture I didn't make myself.<br />
<br />[[file:Water-electricity.gif|thumb|500px|center|It may help to read the derived units section to understand the units used on the water side.]]<br />
<br />
===Application of Ohm's law===<br />
This section doesn't teach any theory behind Ohm's law, but this is one of the easiest ways to apply the law(or the power law(P=IV), or any similar law). Basically, take a circle and divide into half, then divide one of the halfs in half again(so you have half a circle at the top, and two quarters at the bottom).<br />
Then you put the equation(any equation in the form a=bc), in the case of the power law, P would go into the half, and I and V would go into quarters. Now all you have to do to find a certain value is cover up what you're looking for(for example,finding I using P and V) and look at the 2 uncovered letters, in the example, P and V are uncovered, since P is on top of V, we know that I=P/V, if the letters are next to each other(i.e. finding P from I and V) then you simply multiply. Sure, the math behind it is very simple, but in a competition this method goes a lot quicker than rearranging equations. <br /><br />This is the basic circle[[File:3pie.gif|thumb|300px|center]]<br /><br /><br />Here's another very useful and much more detailed circle.[[File:circuitpie.gif|thumb|300px|center]]<br />
<br />
==Sources==<br />
'''Voltage Sources'''<br />
A voltage source is a theoretical component which outputs a precise, constant voltage regardless of current. There primary usage is in modeling real components. For example, a battery can be modeled as a voltage source in series with a resistor equal to its internal resistance.<br />
<br />
'''Current Source'''<br />
A current source is a theoretical component which outputs a precise, constant current, regardless of the voltage. <br />
<br />
<br />
==Resistors==<br />
<br />
Of course, you didn't think that was all there was to resistors, right? Of course not. <br />
<br />
[[Image:Resistors.JPG|thumb|300px|center|This is a basic Â¼ watt resistor, the actual resistor is the part in between the two silver leads]]<br />
<br />
So what can you do with that... Lots, actually. The color bands around the resistor tell you what the resistance is, and what the tolerance is(how accurate it is). The color codes are: <br />
<br />
{|class="wikitable"<br />
|+Resistor Color Codes<br />
!Color<br />
!Value<br />
|-<br />
|Black<br />
|0<br />
|-<br />
|Brown<br />
|1<br />
|-<br />
|Red<br />
|2<br />
|-<br />
|Orange<br />
|3<br />
|-<br />
|Yellow<br />
|4<br />
|-<br />
|Green<br />
|5<br />
|-<br />
|Blue<br />
|6<br />
|-<br />
|Purple(Indigo)<br />
|7<br />
|-<br />
|Gray<br />
|8<br />
|-<br />
|White<br />
|9<br />
|-<br />
|Gold<br />
|.1<br />
|-<br />
|Silver<br />
|.01<br />
|}<br />
{|class="wikitable"<br />
|+Common Tolerance Codes<br />
!Color<br />
!Percent<br />
|-<br />
|Silver<br />
|10%<br />
|-<br />
|Gold<br />
|5%<br />
|-<br />
|Red<br />
|2%<br />
|-<br />
|Brown<br />
|1%<br />
|}<br />
<br />
By the way, the most common tolerance you will see is Gold, followed by Brown, but this doesn't rule out the possibility. To convert the color codes into resistance values(on a resistor with 3 bands and a tolerance band) read the first two bands off in order(in the picture it would be green, then blue, thus 56) and then multiply that by 10^(color of third band), so the picture would be 56x10^0 which is 56 ohms. If the resistor has more than 4 bands, all you do is read the first howevermany(normally 3) until you only have one color(not tolerance) left, and multiply by 10^last color band. <br />
<br />
===Resistor Networks===<br />
Networks of resistors between two points can be simplified into an equivalent single resistor, for which the resistance can be calculated according to the configuration and values of the resistors within the network.<br />
<br />
====Series Resistance====<br />
The resistance of a resistor is directly proportional to the length of the resistive material. As such, because placing resistors in series effectively adds the lengths, resistances add in series. Therefore, for a chain of resistors, the equivalent resistance is equal to the sum of individual resistors.<br />
<br />
====Parallel Resistance====<br />
In parallel, it is not the resistances that add, but the conductances. An analogy for this is to imagine a crowd of people trying to get through a door. A single door will allow so many people per minute, but if a second, adjacent, identical door is opened, the same number of people per minute will simultaneously move through that door. Therefore, twice the number of people will move through the doors per minute. Similarly, two identical resistors in parallel will conduct twice the current as a single one. Therefore the total conductance is equal to the sum of individual conductances in parallel. As conductance is the reciprocal of resistance, the usual formula is that 1/Rt=1/R1+1/R2+...+1/Rn for n resistors in parallel.<br />
<br />
''''Networks Containing Both Series and Parallel'''<br />
Many real circuits will contain a combination of both series and parallel components. To simplify these networks, one must find parts of the networks that are purely one or the other and simplify them according to the formulas above. One can repeat this process until the network is simplified into a single equivalent resistor.<br />
<br />
===Wheatstone Bridge===<br />
A wheatstone bridge is used to measure an unknown resistance value to a high degree of accuracy. It uses 4 resistors set up in a diamond fashion(shown below) and a voltmeter. In the schematic below, Rx is the unkown resistance, R1 and R3 are fixed resistance values(generally the same, but they don't have to be the same, also generally >1% tolerance, but again, not always) and R2 is a variable resistor(potentiometer, this is not always the case, see below). By adjusting R2 until the voltmeter reads 0 volts, you know that the ratio between the R1/R2 and R3/Rx is equal.<br /><br /><br />
[[file:500px-Wheatstonebridge.svg.png|thumb|300px|center|Wheatstone Bridge Schematic(Courtesy Wikipedia)]]<br /><br /><br />
To understand this, think of a circuit with two resistors of equal value in series, connected to a +5v source, becuase the resistances are equal, the voltage droop is equal, this kind of circuit is called a voltage divider, becuase the voltage in between the two resistors is 1/2 the input voltage. Again, imagine a circuit with 2 resistors in series connected to a +5v source, however this time, the resistors are 50 ohms and 25 ohms, becuase the total resistence (remember series resistance?) is 75 ohms, at 5v, we can calculate the current, and from there calculate the voltage drop from each resistor, you should have gotten 3.33 volts across the first, and 1.66 for the second one (I tried to pick better numbers, honest!); well, the voltage happens to be in the same ratio as the resistance values; now that we've proved that, we can apply it to the wheatstone bridge.<br /><br /><br />
With that in mind, we now know that the ratio of the resistors is what controls the voltage at the midpoint, so if two sets of resistors have the same ratio, then they would have the same voltage, see where I'm going? When the voltage across the bridge is 0, the sets of resistors(R1/R2 and R3/Rx) have the same voltage, and thus the same ratio of resistance values! Since we know the ratio of the first leg(R1/R2, remember we set R2 to a known value to balance the bridge...) and we know R3, it's fairly simple to solve for Rx.<br /><br /><br />
Now here's the fun part... What if you don't want to have to change R2? Well then, you can, using the same principle, take the voltage across the bridge, and calculate Rx from that... I'll leave out the derivation (Hey, it'd make good practice!), but basically, by applying all the concepts discussed here (Kirchhoff's laws, Ohm's law, etc) you end up at the equation <br /> <math>V_G = ({R_x \over {R_3 + R_x}} - {R_2 \over {R_1 + R_2}})</math><br />
<br />
==Kirchhoff's Laws==<br />
Kirchhoff has two well-known laws of circuits: '''Kirchhoff's Current Law''' (KCL) and '''Kirchhoff's Voltage Law''' (KVL). They are simplifications of Maxwell's Laws of Electromagnetism that are valid for most practical circuits.<br />
<br />
<br />
===Kirchhoff's Current Law===<br />
A '''node''' is a junction in a circuit where two or more electrical components meet. '''Kirchhoff's Current Law''' states that sum of currents entering a node is equal to the sum of currents leaving the node. This is based on the assumption that charges cannot accumulate in a node of the circuit. Equivalently, if one designates the direction of the currents with a sign (eg all currents leaving the node are negative), the sum of currents at each node equals zero.<br />
<br />
====Node Method====<br />
The '''Node Method''' is a powerful tool of circuit analysis that is based upon Kirchhoff's Current Law. Basically, one writes the equation for every node in the circuit based upon unknown variables. Then from the resultant system of equations, one can calculate all the unknown variables and solve the circuit. It is often unnecessary for simple circuits, but becomes quite convenient for large circuits.<br />
<br />
'''Detailed method:'''<br><br />
1. Select a node to be your '''ground''' and assign it a voltage of zero. (N.B. The term "ground" in the context of circuit analysis does not necessarily mean that it is connected to the ground. Instead, it is a node designated at zero electrical potential from which all other voltages are measures.)<br><br />
2. Assign every other node in the circuit a variable voltage. You may in certain cases be able to calculate a voltage for a few nodes (e.g. if the negative terminal of the battery is connected to the ground, the node connected to the positive terminal will have a known, positive voltage).<br><br />
3. Write the KCL equation for every node in the equation. [Example soon].<br><br />
4. Solve the resulting system of equations for all the unknown variables.<br />
At this point, you know the voltage for every node in the circuit and should be able to easily calculate anything else.<br />
<br />
===Kirchhoff's Voltage Law===<br />
'''Kirchhoff's Voltage Law''' (KVL) states that for any closed loop in a circuit, the sum of voltages will be zero. One must be very careful with sign convention for this to work. For example, in a simple series circuit of resistors and voltage sources, one must choose either the voltage sources or the resistors to have negative voltages. This is based on the assumption that there is no changing magnetic field.<br />
<br />
====Mesh Method====<br />
The '''Mesh Method''' is another technique of circuit analysis based upon Kirchhoff's Voltage Law. Essentially, one designates a variable for a current circulating through every loop in the circuit, and then writes an equation for each of these in terms of KVL.<br />
<br />
<br />
<br />
==Equivalent circuits==<br />
Just as networks of individual resistors can be simplified into a single equivalent resistor, so also can more complicated networks. Any network containing resistors, current sources, and voltage sources can be transformed into a Thevenin or Norton equivalent. This is especially useful when analyzing circuits containing other components, as the entire rest of the circuit around the component may be a network which has an equivalent.<br />
===Thevenin equivalent===<br />
The Thevenin equivalent circuit between two points consists of a voltage source in series with a resistor. In order to find the Thevenin voltage, you must find the open-circuit voltage across the two points (ie when it is broken open). The resistance is found by removing all the power sources (replacing current sources with shorts and voltage sources with breaks) and finding the equivalent resistance of the resultant resistor network.<br />
<br />
===Norton equivalent===<br />
The network can also be represented by a Norton equivalent. It consists of a resistor in parallel with a current source. The Norton resistance is equal to the Thevenin resistance. The Norton equivalent current is equal to the current that passes between the two points if you short circuit them.<br />
<br />
==Other Topics==<br />
===Capacitors===<br />
Capacitors are, in DC at least, a device that stores a charge. When capacitors are in a circuit, they are said to resist change in voltage(i.e. if the voltage in a circuit goes up, the capacitor charges, taking away the excess voltage. If the voltage drops, the capacitor discharges, adding back to the circuit to make up the difference. There are many types of capacitors(Mylar, polystyrene, electrolytic, etc), but they all do the same basic job. At the most basic level, a capacitor is comprised of two plates separated by a dielectric(insulting material) that stores a charge, there's a few basic concepts it may be helpful to know. First off, look at the charging circuit below, the capacitor is uncharged in the beginning, but when the switch is closed, it begins to charge, as it starts to charge, the resistance across it is small(thus a current flows through the circuit, charging the capacitor), however as the voltage of the capacitor reaches <math>V_0</math>, the current decays exponentially, because the voltage is smaller, less current flows(remember?). This can also be shown by trying to measure the resistance of a capacitor(see below, because the meter puts out a small current, that charges the capacitor). Its useful to in some cases calculate the voltage for a capacitor as it is charging or discharging, for which 2 formulas are incredibly helpful. For a charging capacitor in an RC circuit Vc = Vo(1-e^(-t/(RC))) and for a discharging one, Vc = Vo(e^(-t/(RC))).<br />[[file:CapCharging.png|thumb|300px|center|Charging circuit, from wikipedia]]<br />
<br />
'''Other Analogy'''<br /><br />
In the water analogy, a capacitor is simulated as a piece of rubber blocking the pipe. Using this example, we can see that a DC current would flow for a time, but when the rubber reached it's elastic limit, it would stop, the same as the capacitor charge curve discussed above. However, an AC current(imagine the water moving back and forth very fast) would simply move the rubber back and forth, never stopping the rubber on the other side from flowing(this is true for electricity, but in an effort to not drone on to long, it's not in there).<br />
<br />
===Inductors===<br />
An inductor is basically an electromagnet, however it exhibits special characteristics in a circuit. In the most simple terms, it's the opposite of a capacitor, however this is slightly misleading. An inductor has an ability to store a charge in a magnetic field(whereas a capacitor stores it in an electric field) and has the ability to maintain a constant current in a circuit(whereas a capacitor can maintain a constant voltage). This means that an inductor can easily conduct DC(whereas a capacitor can easily conduct AC), however if AC is put through an inductor, the magnetic field will grow and collapse with the rise and fall of current, which tends to oppose the flow of AC through an inductor.<br />
<br />
'''Other Analogy'''<br />
In the water analogy, an inductor is a waterwheel, with a constant flow of water through it, the waterwheel spins, and all is fine, however with an alternating flow, the water wheel is continuously trying to turn back and forth, limiting the flow of water.<br />
===Diodes===<br />
Don't let anything in here scare you, you probably only really need to know that a diode conducts only in one way, but hey, it never hurts to know more, right?<br />
This is a topic that's not covered very deeply in the rules, so I will only go over the basics in here. A diode is a semiconductor made of a junction of P-type and N-type silicon(don't worry to much about the details), it's special in that it only conducts in one direction. There are a lot of different types of diodes(schottky, zener, light emmitting diodes) they all vary in a few charecteristics, mainly, their forward voltage drop(how much voltage is lost while conducting), and avalanche voltage(point at which they coduct in reverse), for example, schottky diodes are used in power supplies when you need to combine two power supplies of the same voltage(so one doesn't backfeed the other) because of their charecteristcally low forward voltage drop, whereas zener diodes are used in applications where one needs to detect when a voltage is above a certain point becuase of their low avalanche voltage(put on in backwards and you'll only get a voltage on the other side of it when it crosses a certain point), light emmitting diodes are used... well... you should be able to figure that one out. The arrow on the symbol of a diode points the direction of the conventional (positive) current through the diode.<br /><br /><br />
'''Other Analogy'''<br />
In the water analogy, the diode is simply a check-valve(one way valve). That's it, nothing more to it.<br />
====Circuit Analysis with Ideal Diodes====<br />
Ideal diodes can generally be approximated by either a short or a break in the circuit. Generally to analyze a circuit with an ideal diode, one will make an educated guess on whether or not the diode will conduct. Once one finds a solution for this hypothesized circuit, one much check whether it makes sense. If you assumed the diode would conduct, you must make sure it is conducting current in the correct direction. If you assumed it does not conduct, you must check to make sure the voltage across the hypothetically non-conducting diode is such that it would not conduct. If this is not the case, you must switch your assumption and recalculate the circuit.<br />
<br />
===Base and Derived Units===<br />
SI base units are the base quantities that are independent. There is a total of seven units, but the ones important to this event are meters (m, length), kilograms (kg, mass), amperes (A, electric current), and seconds (s, time). Derived units are units that come from a combination of the base units. The ones important to this event are newtons, joules, watts, coulombs, volts, farads, siemens, and ohms. The table below shows how each of the units is related. <br />
<br />
{|class="wikitable"<br />
|+Derived Units<br />
!Quantity measured<br />
!Unit name<br />
!Unit symbol<br />
!Expression in other SI Units<br />
!Base SI Units<br />
|-<br />
|Electrostatic Force<br />
|Newton<br />
|N<br />
| -<br />
|kg*m*s<sup>-2</sup><br />
|-<br />
|Energy, work<br />
|Joule<br />
|J<br />
|N*m<br />
|m<sup>2</sup>*kg*s<sup>-2</sup><br />
|-<br />
|Power<br />
|Watt<br />
|W<br />
|J/s<br />
|m<sup>2</sup>*kg*s<sup>-3</sup><br />
|-<br />
|Electric Charge<br />
|Coulomb<br />
|C<br />
| - <br />
|s*A<br />
|-<br />
|Electric Potential Difference<br />
|Volt<br />
|V<br />
|W/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-1</sup><br />
|-<br />
|Capacitance<br />
|Farad<br />
|F<br />
|C/V<br />
|s<sup>4</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|Electric Resistance<br />
|Ohm<br />
|Î©<br />
|V/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-2</sup><br />
|-<br />
|Electric Conductance<br />
|Sieman<br />
|S<br />
|A/V<br />
|s<sup>3</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|}<br />
<br />
Another important derived quantity that does not have a special unit name is the electric field strength, measured in V/m.<br><br />
One coulomb is also equal to the charge of 6.24 x 10<sup>18</sup> electrons.<br />
<br />
===Meters===<br />
[[file:Meter.JPG|thumb|300px|center|This is a fairly complex Fluke 287 multimeter, note the separate jacks for measuring current.]]<br />
<br />
During the event, the test may require you to measure certain values in a circuit, for this you can use either a multimeter or probes(whatever the ES gives you), but you have to know how to hook it up, or you could get yourself dq'd(I've seen this happen). Basically, there are three things that you could be asked to measure, voltage, current, or resistance. <br /><br /><br />
'''Voltage''' is fairly straightforward, you put the said device in voltage mode(make sure the probes are hooked up in the right place!) and put them across whatever you want to measure and it reads off a voltage(the difference in potential between the probes, the meter has a high enough resistance(called impedance) that it won't cause any significant amount of current to flow(most meters are around 11 million ohms!)). <br /><br /><br />
'''Current''' is another one you might be asked to measure, think of current as the flow-rate in the water analogy, to measure the flow, you have to 'get into' the circuit, this is why meters have a separate jack for current, there's a fuse in between the current jack and the common, and a low value(<5 ohms), by connecting the leads to the circuit, you allow current to flow with minimal resistance. The resistor in the circuit is called a shunt(that's just a big term for a resistor used to measure current) and by measuring the voltage across it, you can calculate the current(because the resistor has a constant value). Never put a meter set up to measure current in parallel with part of the circuit. You might blow a fuse in the meter or worse.<br /><br /><br />
'''Resistance''' is a little trickier, it can help to understand how the meter's going to measure it, basically, it puts out a small voltage(~2-3v) and measures the current that flows in the circuit, and calculates the resistance. This means that you can't measure resistance with power on the circuit, and you have to account for all the possible paths, not just the most direct route. Generally, one must first disconnect a component from the circuit before measuring the resistance. Never put an external voltage across a meter in resistance mode, as this could damage the meter.<br />
<br />
===AC Power===<br />
For more info, see [[AC Power|this page]].<br /><br/><br />
Up until now, the entire discussion(minus a mention when talking about capacitors) has dealt with DC, or direct current. In a DC circuit, current flows from the positive to the negative terminals of a battery or other source, that it(electrons flow the opposite, see above). However, the power in your house is AC, not DC(unless you live in a very strange house), AC, or alternating current, is a much more complicated beast. Basically, the direction of the current flow change, if you plotted voltage vs time, instead of a line, for DC, you would get a sine wave. This yields many advantages, namely, the use of transformers for voltage step-up/step-down. <br /><br /><br />
'''Transformers'''<br /><br />
Transformers are basically 2 electromagnets that are put together, most of the time sharing a common core of iron. Transformers work because the AC generates a constantly changing magnetic field in the primary coil, which can induce a charge in the secondary coil. It isn't possible to build a DC transformer because the magnetic field would be constant, remember that stable magnetic fields(stationary) can't induce a charge.(a changing field acts the same as a moving one). The ratio of the turns of the primary winding to the turns of the secondary is equal to the ratio of the primary voltage to the secondary(i.e. 2 turns on the primary and 1 on the secondary will half the primary voltage)<br />
<br />
===Digital Logic===<br />
<br />
In digital logic in circuits, a current corresponds to a "true" or "1", and no or very little current corresponds to a "false" or "0". A '''logic gate''' will take 1 or more of these signals, perform a logical operation on it, and then either send a true or a false on its way.<br />
<br />
A simple example of a logic gate is a transistor. If it receives very little current (false/0), then it does not allow current to pass through it (false/0). If it receives a current (true/1), then it allows current to pass through it (true/1).<br />
<br />
Here is a list of logic gates:<br />
*'''AND''' AND must have two trues in order for current to pass through it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A AND B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>A \cdot B</math> or <math>A</math> & <math>B</math>.<br /><br />
Distinctive Shape: [[File:AND logic gate.png]]<br /><br />
Rectangular Shape: [[File:AND rect logic gate.png]]<br />
<br />
*'''OR''' OR will allow current to pass through it if any true is given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A OR B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>A+B</math>. <br /><br />
Distinctive Shape: [[File:OR distinctive logic gate.png]] <br /><br />
Rectangular Shape: [[File:OR rect logic gate.png]]<br />
<br />
*'''NOT''' NOT turns trues into falses and falses into trues. The NOT gate is commonly called an inverter.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!NOT A<br />
|-<br />
|0<br />
|1<br />
|-<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline A</math> or ~<math>A</math>. <br /><br />
Distinctive Shape: [[File: NOT distinctive logic gate.png]]<br /><br />
Rectangular Shape: [[File: NOT rect logic gate.png]]<br />
<br />
*'''NAND''' NAND blocks current only when two trues are given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NAND B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A \cdot B}</math> or <math>A | B</math>.<br /><br />
Distinctive Shape: [[File:NAND distinctive logic gate.png]]<br /><br />
Rectangular Shape: [[File:NAND rect logic gate.png]]<br />
<br />
*'''NOR''' NOR only allows current to pass through it when it is given two falses.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NOR B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A + B}</math> or <math>A - B</math>.<br /><br />
Distinctive Shape: [[File:NOR distinctive logic gate.png]]<br /><br />
Rectangular Shape: [[File:NOR rect logic gate.png]]<br />
<br />
*'''XOR''' XOR only allows current to pass through it when the two signals it is sent are not the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XOR B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>A \oplus B</math>. <br /><br />
Distinctive Shape: [[File:XOR distinctive logic gate.png]]<br /><br />
Rectangular Shape: [[File:XOR rect logic gate.png]]<br />
<br />
*'''XNOR''' XNOR only allows current to pass through it when the two signals it is sent are the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XNOR B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A \oplus B}</math> or <math>A \odot B</math>. <br /><br />
Distinctive Shape: [[File:XNOR distinct logic gate.png]]<br /><br />
Rectangular Shape: [[File:XNOR rect logic gate.png]]<br />
<br />
[http://en.wikipedia.org/wiki/Logic_gate Information Source]<br />
<br />
==Resources==<br />
<br />
The rest of the "episodes" on circuitry, as well as circuit worksheets, can be found [[Circuit Lab (Episodes)|here]].<br />
The rules for a trial event form on Ciruit Lab can be found [http://soinc.org/sites/default/files/uploaded_files/trial_events/CircuitLab.pdf here]<br />
<br />
[[Media:SCIENCE OLYMPIAD CIRCUTE LAB MARCH 7TH.pdf| Circuit Lab Notes]]<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Lab Event Pages]]<br />
[[Category:Electricity/Electronics]]</div>
Voltage
https://scioly.org/wiki/index.php?title=File:XNOR_distinct_logic_gate.png&diff=30703
File:XNOR distinct logic gate.png
2014-04-11T23:25:31Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:AND_rect_logic_gate.png&diff=30702
File:AND rect logic gate.png
2014-04-11T23:24:08Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:XOR_distinctive_logic_gate.png&diff=30701
File:XOR distinctive logic gate.png
2014-04-11T23:13:30Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:NOR_distinctive_logic_gate.png&diff=30700
File:NOR distinctive logic gate.png
2014-04-11T23:13:11Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:NAND_distinctive_logic_gate.png&diff=30699
File:NAND distinctive logic gate.png
2014-04-11T23:12:47Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:NOT_distinctive_logic_gate.png&diff=30698
File:NOT distinctive logic gate.png
2014-04-11T23:12:28Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=File:OR_distinctive_logic_gate.png&diff=30697
File:OR distinctive logic gate.png
2014-04-11T23:12:05Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=Circuit_Lab&diff=30696
Circuit Lab
2014-04-11T23:11:38Z
<p>Voltage: /* Digital Logic */ Adding images</p>
<hr />
<div>{{EventLinksBox<br />
|active=yes<br />
|type=Physics<br />
|cat=Lab<br />
|2009thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=17&t=403 2009]<br />
|2010tests=[http://scioly.org/wiki/2009_Test_Exchange#Shock_Value 2010]<br />
|2010thread=[http://scioly.org/phpBB3/viewtopic.php?f=65&t=1278 2010]<br />
|2011thread=[http://scioly.org/phpBB3/viewtopic.php?f=92&t=2222 2011]<br />
|2011tests=2011<br />
|2013thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=142&t=3691 2013]<br />
|2013tests=2013<br />
|2014thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=166&t=4951 2014]<br />
|2014tests=2014<br />
|2014questions=[http://www.scioly.org/phpBB3/viewtopic.php?f=173&t=5022 2014]<br />
|B Champion=[[Daniel Wright Junior High School]]<br />
|C Champion=[[Harriton High School]]<br />
}}<br />
==Introduction==<br />
Circuit Lab is a laboratory event which deals with the various components and properties of direct current (DC) circuits. Historically, the fields which have been tested in this event are DC circuit concepts and DC circuit analysis (both theory and practice).<br />
<br />
==What is a Circuit?==<br />
Let's take an example of a battery, for now. The battery has a positive (+) end, and a minus ( - ) end. When you touch a wire onto both ends of the battery at the same time, you have created a circuit. (It is generally ill advised to attempt this experiment. Not only will there be nothing to see, but short-circuiting a battery is potentially dangerous). What just happened? Current flowed from one end of the battery to the other through your wire. Therefore, our definition of circuit can simply be a never-ending looped pathway for electrons (the battery counts as a pathway!).<br />
<br />
'''The Requirement of a Closed Conducting Path'''<br />
<br />
There are two requirements which must be met to establish an electric circuit. The first is clearly demonstrated by the above activity. There must be a closed conducting path which extends from the positive terminal to the negative terminal. It is not enough that there is a closed connecting loop; the loop itself must extend from the positive terminal to the negative terminal of the electrochemical cell. An electric circuit is like a water circuit at a water park. The flow of charge through the wires is similar to the flow of water through the pipes and along the slides of the water park. If a pipe gets plugged or broken such that water cannot make a complete path through the circuit, then the flow of water will soon cease. In an electric circuit, all connections must be made and made by conducting materials capable of carrying charge. Metallic materials are conductors and can be inserted into the circuit to successfully light the bulb. There must be a closed conducting loop from the positive to the negative terminal in order to establish a circuit and to have a current.<br />
<br />
==Basic Electrical DC Circuit Theory==<br />
===Current Flow and Direction===<br />
'''"Conventional Current Flow" vs. "Electron Flow"''' - This has to do with how circuit diagrams are interpreted. Now, remember we said that electrons are 'flowing' in the wires? The question here deals with : Do they 'flow' from the positive end of the battery, or the negative end of the battery?<br />
<br />
Just as where in mathematics subtracting a negative is equivalent to adding a negative, so also a flow of positive charges in one direction is the exact same current as a flow of negative charges in the opposite direction. As such in most applications, the choice of current direction is an arbitrary convention.<br />
<br />
Conventional current flow, devised by Benjamin Franklin, views the current as a "flow" of positive charges. Therefore, this concept holds that current "flows" out of the positive end of the battery. Electron flow, on the other hand, deals with the ACTUAL route of the electrons (the primary carrier of electric charge in most circuits). Being negatively charged particles, electron currents moves out of the negative end of the battery.<br />
<br />
===Current===<br />
<br />
What is an "electron?" To put it simply, an electron is an atomic particle which carries a negative charge. These electrons spin around the nucleus of an atom, which has a positive charge, and is located in the very center of the atom. The concept of "electricity" has to do with these electrons and with their "electron flow." Do you remember the example of our battery? This battery takes these negatively charged electrons from a chemical reaction inside the battery, pushes them out of the negative end of the battery, and into the wire. These electrons will then bump electrons in the atoms of the wire over and over until finally electrons arrive back at the positive end of the battery. Elements which allow this process of "bumping" those electrons on over determines how conductive the element is. So, when there's a current, it's just electrons bumping each other from atom to atom and flowing on. The individual electrons generally move very slowly, but the electric current moves at the speed of light.<br />
<br />
<br />
A circuit requires a loop for the electrons to travel on (think of "circle"). This means you can not simply attach a wire to one end of a battery and expect electrons to flow through it. As stated before, in our definition of the circuit, a continuous loop is required. But think about it scientifically: If you did attach the wire to only one end of the battery, where would the electrons go that got bumped to the opposite end of the wire? That is why there needs to be that continuous loop of wire: the electrons need somewhere to go.<br />
<br />
==Voltage, Resistance, and Amperes==<br />
<br />
''For more in-depth information, see [[Circuit Lab (Episodes)|Episode 1]]''<br />
<br />
===Amperes(Symbol I or rarely A)=== <br />
To consider Amps pretend that you are the coach of a baseball team. You want to make your team the best that it can be. There are two ways you can do this, making your team score as much as possible and making the opposing team score as little as possible. Focusing on both would be impossible so naturally you're going to have to choose one area to focus on: say you want to score more runs; let's relate this to the concept of "amperes." The amount of runs you make is your score - the more you get the better your chance of winning. Similarly, amperes measure the amount of current you have flowing per second through an area: is it a lot, or a little bit? Now, if you want to win the game, you don't necessarily have to score a whole lot of runs, you just need to score more than your opponent. So, maybe your resistance to their scoring of runs will be high - and resistance to current flowing is also one of our important terms we need to know. Now, how do these concepts of amperes and resistance relate, straying from the daemons for now? If you multiply the resistance by the amperes, you have the voltage of a circuit (remember, we're always talking about in circuits here, not on a baseball field). This relationship was discovered by Georg Simon Ohm, and it says, simply, that: <br />
<br />
<math>V = I \times R</math> <br />
<br />
Or <br />
<br />
Voltage = Current times Resistance <br />
<br />
*Sometimes E is used in place of V, for electromotive force(EMF), it's the same thing, don't worry.<br />
<br />
[[File:Cool Story.png]]<br />
<br />
===Voltage(V or sometimes E)===<br />
Imagine a battery as a super-soaker, and the water that comes out of it as voltage. The harder you pump that super-soaker, the harder that stream is going to be when it comes out of the gun. Voltage is the potential for that water to go very quickly out of the gun: the more you pumped, putting more "voltage" in, the faster that water will go: but sometimes you will have a "multi-functioning" nozzle which even allows you to adjust that water speed even further. You want the water to go out in a "wider" and "bigger" stream, you might change the nozzle to a bigger opening. What you've just done is changed the amount of space that the water is allowed to go through: the water is now given a much bigger space to flow through. The "voltage," or potential, of the water to go fast and give bruises is still high, but now you've taken away from its hitting-power by spreading it out. Anyone know where I'm going next with this? The bigger your nozzle gets (think of it like the resistance), the smaller the hitting power (current (which is a speed in electricity too!)) is going to be.<br />
<br />
Voltage is technically electrical potential. While in many cases we treat it as an absolute, it is important to remember that in circuits we talk mostly about the difference in voltage, a potential difference, and that things like Ohm's laws only apply to potential ''differences'' not just electrical potential. However, in the context of circuits, Voltage is often used in reference to potential difference.<br />
<br />
=== Resistance(Î©)=== <br />
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A resistor is just a piece of metal, and the piece in the center there is what provides the resistance.<br />
<br />
And as for what resistance is itself - it is the force against the flow of the electrons. They transform the electrical energy they absorb into heat energy.<br />
<br />
Imagine our electrons - flowing along the wire, pushing new electrons to flow on, and so on. This wire is not very hard to flow in - it's made of a material that's very conductive. But what would happen if we placed something in the middle of the wire that was harder for the electrons to flow through? They're going to be bumping into all the atoms in the material, which will cause the atoms to vibrate. This, in turn, will cause nearby air molecules to take some energy. That energy is in the form of heat. Where did it come from again? From the electrons bumping into atoms inside the resistor. <br />
<br />
===Other Analogy===<br />
The other way that these three are explained is using water as an example. Imagine the basic components of a circuit, a battery, wire, and say, a resistor. In the water analogy, this translates to a pump(because the battery pushes electrons around the circuit), some large pipe(wire), and a section of much smaller pipe(resistor). We know that in the water analogy, the flow rate of the pump is the same as the voltage of the battery, and the pressure in the tubing if the same as the current in the circuit. This is a pretty simple way to explain voltage/current/ and resistance. If we up the voltage, but keep the resistance(pipe size) the same, it logically takes more pressure, however if we keep the flow rate the same and put in large pipes, it takes a lot less pressure to so the same job. Conversely, if we drop the pressure, but keep the same pipe size, the flow rate goes down, and if we maintain constant pressure, but increase the pipe size, the flow rate goes up. And that's all there is to it. Thus we can see the relationships in Ohm's law. Here a fancy picture I didn't make myself.<br />
<br />[[file:Water-electricity.gif|thumb|500px|center|It may help to read the derived units section to understand the units used on the water side.]]<br />
<br />
===Application of Ohm's law===<br />
This section doesn't teach any theory behind Ohm's law, but this is one of the easiest ways to apply the law(or the power law(P=IV), or any similar law). Basically, take a circle and divide into half, then divide one of the halfs in half again(so you have half a circle at the top, and two quarters at the bottom).<br />
Then you put the equation(any equation in the form a=bc), in the case of the power law, P would go into the half, and I and V would go into quarters. Now all you have to do to find a certain value is cover up what you're looking for(for example,finding I using P and V) and look at the 2 uncovered letters, in the example, P and V are uncovered, since P is on top of V, we know that I=P/V, if the letters are next to each other(i.e. finding P from I and V) then you simply multiply. Sure, the math behind it is very simple, but in a competition this method goes a lot quicker than rearranging equations. <br /><br />This is the basic circle[[File:3pie.gif|thumb|300px|center]]<br /><br /><br />Here's another very useful and much more detailed circle.[[File:circuitpie.gif|thumb|300px|center]]<br />
<br />
==Sources==<br />
'''Voltage Sources'''<br />
A voltage source is a theoretical component which outputs a precise, constant voltage regardless of current. There primary usage is in modeling real components. For example, a battery can be modeled as a voltage source in series with a resistor equal to its internal resistance.<br />
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'''Current Source'''<br />
A current source is a theoretical component which outputs a precise, constant current, regardless of the voltage. <br />
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<br />
==Resistors==<br />
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Of course, you didn't think that was all there was to resistors, right? Of course not. <br />
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[[Image:Resistors.JPG|thumb|300px|center|This is a basic Â¼ watt resistor, the actual resistor is the part in between the two silver leads]]<br />
<br />
So what can you do with that... Lots, actually. The color bands around the resistor tell you what the resistance is, and what the tolerance is(how accurate it is). The color codes are: <br />
<br />
{|class="wikitable"<br />
|+Resistor Color Codes<br />
!Color<br />
!Value<br />
|-<br />
|Black<br />
|0<br />
|-<br />
|Brown<br />
|1<br />
|-<br />
|Red<br />
|2<br />
|-<br />
|Orange<br />
|3<br />
|-<br />
|Yellow<br />
|4<br />
|-<br />
|Green<br />
|5<br />
|-<br />
|Blue<br />
|6<br />
|-<br />
|Purple(Indigo)<br />
|7<br />
|-<br />
|Gray<br />
|8<br />
|-<br />
|White<br />
|9<br />
|-<br />
|Gold<br />
|.1<br />
|-<br />
|Silver<br />
|.01<br />
|}<br />
{|class="wikitable"<br />
|+Common Tolerance Codes<br />
!Color<br />
!Percent<br />
|-<br />
|Silver<br />
|10%<br />
|-<br />
|Gold<br />
|5%<br />
|-<br />
|Red<br />
|2%<br />
|-<br />
|Brown<br />
|1%<br />
|}<br />
<br />
By the way, the most common tolerance you will see is Gold, followed by Brown, but this doesn't rule out the possibility. To convert the color codes into resistance values(on a resistor with 3 bands and a tolerance band) read the first two bands off in order(in the picture it would be green, then blue, thus 56) and then multiply that by 10^(color of third band), so the picture would be 56x10^0 which is 56 ohms. If the resistor has more than 4 bands, all you do is read the first howevermany(normally 3) until you only have one color(not tolerance) left, and multiply by 10^last color band. <br />
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===Resistor Networks===<br />
Networks of resistors between two points can be simplified into an equivalent single resistor, for which the resistance can be calculated according to the configuration and values of the resistors within the network.<br />
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====Series Resistance====<br />
The resistance of a resistor is directly proportional to the length of the resistive material. As such, because placing resistors in series effectively adds the lengths, resistances add in series. Therefore, for a chain of resistors, the equivalent resistance is equal to the sum of individual resistors.<br />
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====Parallel Resistance====<br />
In parallel, it is not the resistances that add, but the conductances. An analogy for this is to imagine a crowd of people trying to get through a door. A single door will allow so many people per minute, but if a second, adjacent, identical door is opened, the same number of people per minute will simultaneously move through that door. Therefore, twice the number of people will move through the doors per minute. Similarly, two identical resistors in parallel will conduct twice the current as a single one. Therefore the total conductance is equal to the sum of individual conductances in parallel. As conductance is the reciprocal of resistance, the usual formula is that 1/Rt=1/R1+1/R2+...+1/Rn for n resistors in parallel.<br />
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''''Networks Containing Both Series and Parallel'''<br />
Many real circuits will contain a combination of both series and parallel components. To simplify these networks, one must find parts of the networks that are purely one or the other and simplify them according to the formulas above. One can repeat this process until the network is simplified into a single equivalent resistor.<br />
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===Wheatstone Bridge===<br />
A wheatstone bridge is used to measure an unknown resistance value to a high degree of accuracy. It uses 4 resistors set up in a diamond fashion(shown below) and a voltmeter. In the schematic below, Rx is the unkown resistance, R1 and R3 are fixed resistance values(generally the same, but they don't have to be the same, also generally >1% tolerance, but again, not always) and R2 is a variable resistor(potentiometer, this is not always the case, see below). By adjusting R2 until the voltmeter reads 0 volts, you know that the ratio between the R1/R2 and R3/Rx is equal.<br /><br /><br />
[[file:500px-Wheatstonebridge.svg.png|thumb|300px|center|Wheatstone Bridge Schematic(Courtesy Wikipedia)]]<br /><br /><br />
To understand this, think of a circuit with two resistors of equal value in series, connected to a +5v source, becuase the resistances are equal, the voltage droop is equal, this kind of circuit is called a voltage divider, becuase the voltage in between the two resistors is 1/2 the input voltage. Again, imagine a circuit with 2 resistors in series connected to a +5v source, however this time, the resistors are 50 ohms and 25 ohms, becuase the total resistence (remember series resistance?) is 75 ohms, at 5v, we can calculate the current, and from there calculate the voltage drop from each resistor, you should have gotten 3.33 volts across the first, and 1.66 for the second one (I tried to pick better numbers, honest!); well, the voltage happens to be in the same ratio as the resistance values; now that we've proved that, we can apply it to the wheatstone bridge.<br /><br /><br />
With that in mind, we now know that the ratio of the resistors is what controls the voltage at the midpoint, so if two sets of resistors have the same ratio, then they would have the same voltage, see where I'm going? When the voltage across the bridge is 0, the sets of resistors(R1/R2 and R3/Rx) have the same voltage, and thus the same ratio of resistance values! Since we know the ratio of the first leg(R1/R2, remember we set R2 to a known value to balance the bridge...) and we know R3, it's fairly simple to solve for Rx.<br /><br /><br />
Now here's the fun part... What if you don't want to have to change R2? Well then, you can, using the same principle, take the voltage across the bridge, and calculate Rx from that... I'll leave out the derivation (Hey, it'd make good practice!), but basically, by applying all the concepts discussed here (Kirchhoff's laws, Ohm's law, etc) you end up at the equation <br /> <math>V_G = ({R_x \over {R_3 + R_x}} - {R_2 \over {R_1 + R_2}})</math><br />
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==Kirchhoff's Laws==<br />
Kirchhoff has two well-known laws of circuits: '''Kirchhoff's Current Law''' (KCL) and '''Kirchhoff's Voltage Law''' (KVL). They are simplifications of Maxwell's Laws of Electromagnetism that are valid for most practical circuits.<br />
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<br />
===Kirchhoff's Current Law===<br />
A '''node''' is a junction in a circuit where two or more electrical components meet. '''Kirchhoff's Current Law''' states that sum of currents entering a node is equal to the sum of currents leaving the node. This is based on the assumption that charges cannot accumulate in a node of the circuit. Equivalently, if one designates the direction of the currents with a sign (eg all currents leaving the node are negative), the sum of currents at each node equals zero.<br />
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====Node Method====<br />
The '''Node Method''' is a powerful tool of circuit analysis that is based upon Kirchhoff's Current Law. Basically, one writes the equation for every node in the circuit based upon unknown variables. Then from the resultant system of equations, one can calculate all the unknown variables and solve the circuit. It is often unnecessary for simple circuits, but becomes quite convenient for large circuits.<br />
<br />
'''Detailed method:'''<br><br />
1. Select a node to be your '''ground''' and assign it a voltage of zero. (N.B. The term "ground" in the context of circuit analysis does not necessarily mean that it is connected to the ground. Instead, it is a node designated at zero electrical potential from which all other voltages are measures.)<br><br />
2. Assign every other node in the circuit a variable voltage. You may in certain cases be able to calculate a voltage for a few nodes (e.g. if the negative terminal of the battery is connected to the ground, the node connected to the positive terminal will have a known, positive voltage).<br><br />
3. Write the KCL equation for every node in the equation. [Example soon].<br><br />
4. Solve the resulting system of equations for all the unknown variables.<br />
At this point, you know the voltage for every node in the circuit and should be able to easily calculate anything else.<br />
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===Kirchhoff's Voltage Law===<br />
'''Kirchhoff's Voltage Law''' (KVL) states that for any closed loop in a circuit, the sum of voltages will be zero. One must be very careful with sign convention for this to work. For example, in a simple series circuit of resistors and voltage sources, one must choose either the voltage sources or the resistors to have negative voltages. This is based on the assumption that there is no changing magnetic field.<br />
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====Mesh Method====<br />
The '''Mesh Method''' is another technique of circuit analysis based upon Kirchhoff's Voltage Law. Essentially, one designates a variable for a current circulating through every loop in the circuit, and then writes an equation for each of these in terms of KVL.<br />
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<br />
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==Equivalent circuits==<br />
Just as networks of individual resistors can be simplified into a single equivalent resistor, so also can more complicated networks. Any network containing resistors, current sources, and voltage sources can be transformed into a Thevenin or Norton equivalent. This is especially useful when analyzing circuits containing other components, as the entire rest of the circuit around the component may be a network which has an equivalent.<br />
===Thevenin equivalent===<br />
The Thevenin equivalent circuit between two points consists of a voltage source in series with a resistor. In order to find the Thevenin voltage, you must find the open-circuit voltage across the two points (ie when it is broken open). The resistance is found by removing all the power sources (replacing current sources with shorts and voltage sources with breaks) and finding the equivalent resistance of the resultant resistor network.<br />
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===Norton equivalent===<br />
The network can also be represented by a Norton equivalent. It consists of a resistor in parallel with a current source. The Norton resistance is equal to the Thevenin resistance. The Norton equivalent current is equal to the current that passes between the two points if you short circuit them.<br />
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==Other Topics==<br />
===Capacitors===<br />
Capacitors are, in DC at least, a device that stores a charge. When capacitors are in a circuit, they are said to resist change in voltage(i.e. if the voltage in a circuit goes up, the capacitor charges, taking away the excess voltage. If the voltage drops, the capacitor discharges, adding back to the circuit to make up the difference. There are many types of capacitors(Mylar, polystyrene, electrolytic, etc), but they all do the same basic job. At the most basic level, a capacitor is comprised of two plates separated by a dielectric(insulting material) that stores a charge, there's a few basic concepts it may be helpful to know. First off, look at the charging circuit below, the capacitor is uncharged in the beginning, but when the switch is closed, it begins to charge, as it starts to charge, the resistance across it is small(thus a current flows through the circuit, charging the capacitor), however as the voltage of the capacitor reaches <math>V_0</math>, the current decays exponentially, because the voltage is smaller, less current flows(remember?). This can also be shown by trying to measure the resistance of a capacitor(see below, because the meter puts out a small current, that charges the capacitor). Its useful to in some cases calculate the voltage for a capacitor as it is charging or discharging, for which 2 formulas are incredibly helpful. For a charging capacitor in an RC circuit Vc = Vo(1-e^(-t/(RC))) and for a discharging one, Vc = Vo(e^(-t/(RC))).<br />[[file:CapCharging.png|thumb|300px|center|Charging circuit, from wikipedia]]<br />
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'''Other Analogy'''<br /><br />
In the water analogy, a capacitor is simulated as a piece of rubber blocking the pipe. Using this example, we can see that a DC current would flow for a time, but when the rubber reached it's elastic limit, it would stop, the same as the capacitor charge curve discussed above. However, an AC current(imagine the water moving back and forth very fast) would simply move the rubber back and forth, never stopping the rubber on the other side from flowing(this is true for electricity, but in an effort to not drone on to long, it's not in there).<br />
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===Inductors===<br />
An inductor is basically an electromagnet, however it exhibits special characteristics in a circuit. In the most simple terms, it's the opposite of a capacitor, however this is slightly misleading. An inductor has an ability to store a charge in a magnetic field(whereas a capacitor stores it in an electric field) and has the ability to maintain a constant current in a circuit(whereas a capacitor can maintain a constant voltage). This means that an inductor can easily conduct DC(whereas a capacitor can easily conduct AC), however if AC is put through an inductor, the magnetic field will grow and collapse with the rise and fall of current, which tends to oppose the flow of AC through an inductor.<br />
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'''Other Analogy'''<br />
In the water analogy, an inductor is a waterwheel, with a constant flow of water through it, the waterwheel spins, and all is fine, however with an alternating flow, the water wheel is continuously trying to turn back and forth, limiting the flow of water.<br />
===Diodes===<br />
Don't let anything in here scare you, you probably only really need to know that a diode conducts only in one way, but hey, it never hurts to know more, right?<br />
This is a topic that's not covered very deeply in the rules, so I will only go over the basics in here. A diode is a semiconductor made of a junction of P-type and N-type silicon(don't worry to much about the details), it's special in that it only conducts in one direction. There are a lot of different types of diodes(schottky, zener, light emmitting diodes) they all vary in a few charecteristics, mainly, their forward voltage drop(how much voltage is lost while conducting), and avalanche voltage(point at which they coduct in reverse), for example, schottky diodes are used in power supplies when you need to combine two power supplies of the same voltage(so one doesn't backfeed the other) because of their charecteristcally low forward voltage drop, whereas zener diodes are used in applications where one needs to detect when a voltage is above a certain point becuase of their low avalanche voltage(put on in backwards and you'll only get a voltage on the other side of it when it crosses a certain point), light emmitting diodes are used... well... you should be able to figure that one out. The arrow on the symbol of a diode points the direction of the conventional (positive) current through the diode.<br /><br /><br />
'''Other Analogy'''<br />
In the water analogy, the diode is simply a check-valve(one way valve). That's it, nothing more to it.<br />
====Circuit Analysis with Ideal Diodes====<br />
Ideal diodes can generally be approximated by either a short or a break in the circuit. Generally to analyze a circuit with an ideal diode, one will make an educated guess on whether or not the diode will conduct. Once one finds a solution for this hypothesized circuit, one much check whether it makes sense. If you assumed the diode would conduct, you must make sure it is conducting current in the correct direction. If you assumed it does not conduct, you must check to make sure the voltage across the hypothetically non-conducting diode is such that it would not conduct. If this is not the case, you must switch your assumption and recalculate the circuit.<br />
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===Base and Derived Units===<br />
SI base units are the base quantities that are independent. There is a total of seven units, but the ones important to this event are meters (m, length), kilograms (kg, mass), amperes (A, electric current), and seconds (s, time). Derived units are units that come from a combination of the base units. The ones important to this event are newtons, joules, watts, coulombs, volts, farads, siemens, and ohms. The table below shows how each of the units is related. <br />
<br />
{|class="wikitable"<br />
|+Derived Units<br />
!Quantity measured<br />
!Unit name<br />
!Unit symbol<br />
!Expression in other SI Units<br />
!Base SI Units<br />
|-<br />
|Electrostatic Force<br />
|Newton<br />
|N<br />
| -<br />
|kg*m*s<sup>-2</sup><br />
|-<br />
|Energy, work<br />
|Joule<br />
|J<br />
|N*m<br />
|m<sup>2</sup>*kg*s<sup>-2</sup><br />
|-<br />
|Power<br />
|Watt<br />
|W<br />
|J/s<br />
|m<sup>2</sup>*kg*s<sup>-3</sup><br />
|-<br />
|Electric Charge<br />
|Coulomb<br />
|C<br />
| - <br />
|s*A<br />
|-<br />
|Electric Potential Difference<br />
|Volt<br />
|V<br />
|W/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-1</sup><br />
|-<br />
|Capacitance<br />
|Farad<br />
|F<br />
|C/V<br />
|s<sup>4</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|Electric Resistance<br />
|Ohm<br />
|Î©<br />
|V/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-2</sup><br />
|-<br />
|Electric Conductance<br />
|Sieman<br />
|S<br />
|A/V<br />
|s<sup>3</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|}<br />
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Another important derived quantity that does not have a special unit name is the electric field strength, measured in V/m.<br><br />
One coulomb is also equal to the charge of 6.24 x 10<sup>18</sup> electrons.<br />
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===Meters===<br />
[[file:Meter.JPG|thumb|300px|center|This is a fairly complex Fluke 287 multimeter, note the separate jacks for measuring current.]]<br />
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During the event, the test may require you to measure certain values in a circuit, for this you can use either a multimeter or probes(whatever the ES gives you), but you have to know how to hook it up, or you could get yourself dq'd(I've seen this happen). Basically, there are three things that you could be asked to measure, voltage, current, or resistance. <br /><br /><br />
'''Voltage''' is fairly straightforward, you put the said device in voltage mode(make sure the probes are hooked up in the right place!) and put them across whatever you want to measure and it reads off a voltage(the difference in potential between the probes, the meter has a high enough resistance(called impedance) that it won't cause any significant amount of current to flow(most meters are around 11 million ohms!)). <br /><br /><br />
'''Current''' is another one you might be asked to measure, think of current as the flow-rate in the water analogy, to measure the flow, you have to 'get into' the circuit, this is why meters have a separate jack for current, there's a fuse in between the current jack and the common, and a low value(<5 ohms), by connecting the leads to the circuit, you allow current to flow with minimal resistance. The resistor in the circuit is called a shunt(that's just a big term for a resistor used to measure current) and by measuring the voltage across it, you can calculate the current(because the resistor has a constant value). Never put a meter set up to measure current in parallel with part of the circuit. You might blow a fuse in the meter or worse.<br /><br /><br />
'''Resistance''' is a little trickier, it can help to understand how the meter's going to measure it, basically, it puts out a small voltage(~2-3v) and measures the current that flows in the circuit, and calculates the resistance. This means that you can't measure resistance with power on the circuit, and you have to account for all the possible paths, not just the most direct route. Generally, one must first disconnect a component from the circuit before measuring the resistance. Never put an external voltage across a meter in resistance mode, as this could damage the meter.<br />
<br />
===AC Power===<br />
For more info, see [[AC Power|this page]].<br /><br/><br />
Up until now, the entire discussion(minus a mention when talking about capacitors) has dealt with DC, or direct current. In a DC circuit, current flows from the positive to the negative terminals of a battery or other source, that it(electrons flow the opposite, see above). However, the power in your house is AC, not DC(unless you live in a very strange house), AC, or alternating current, is a much more complicated beast. Basically, the direction of the current flow change, if you plotted voltage vs time, instead of a line, for DC, you would get a sine wave. This yields many advantages, namely, the use of transformers for voltage step-up/step-down. <br /><br /><br />
'''Transformers'''<br /><br />
Transformers are basically 2 electromagnets that are put together, most of the time sharing a common core of iron. Transformers work because the AC generates a constantly changing magnetic field in the primary coil, which can induce a charge in the secondary coil. It isn't possible to build a DC transformer because the magnetic field would be constant, remember that stable magnetic fields(stationary) can't induce a charge.(a changing field acts the same as a moving one). The ratio of the turns of the primary winding to the turns of the secondary is equal to the ratio of the primary voltage to the secondary(i.e. 2 turns on the primary and 1 on the secondary will half the primary voltage)<br />
<br />
===Digital Logic===<br />
<br />
In digital logic in circuits, a current corresponds to a "true" or "1", and no or very little current corresponds to a "false" or "0". A '''logic gate''' will take 1 or more of these signals, perform a logical operation on it, and then either send a true or a false on its way.<br />
<br />
A simple example of a logic gate is a transistor. If it receives very little current (false/0), then it does not allow current to pass through it (false/0). If it receives a current (true/1), then it allows current to pass through it (true/1).<br />
<br />
Here is a list of logic gates:<br />
*'''AND''' AND must have two trues in order for current to pass through it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A AND B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>A \cdot B</math> or <math>A</math> & <math>B</math>.<br /><br />
Distinctive Shape: [[File:AND logic gate.png]]<br />
<br />
*'''OR''' OR will allow current to pass through it if any true is given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A OR B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>A+B</math>. <br /><br />
Distinctive Shape: [[File:OR distinctive logic gate.png]]<br />
<br />
*'''NOT''' NOT turns trues into falses and falses into trues. The NOT gate is commonly called an inverter.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!NOT A<br />
|-<br />
|0<br />
|1<br />
|-<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline A</math> or ~<math>A</math>. <br /><br />
Distinctive Shape: [[File: NOT distinctive logic gate.png]]<br />
<br />
*'''NAND''' NAND blocks current only when two trues are given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NAND B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A \cdot B}</math> or <math>A | B</math>.<br /><br />
Distinctive Shape: [[File:NAND distinctive logic gate.png]]<br />
<br />
*'''NOR''' NOR only allows current to pass through it when it is given two falses.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NOR B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A + B}</math> or <math>A - B</math>.<br /><br />
Distinctive Shape: [[File:NOR distinctive logic gate.png]]<br />
<br />
*'''XOR''' XOR only allows current to pass through it when the two signals it is sent are not the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XOR B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>A \oplus B</math>. <br /><br />
Distinctive Shape: [[File:XOR distinctive logic gate.png]]<br />
<br />
*'''XNOR''' XNOR only allows current to pass through it when the two signals it is sent are the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XNOR B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A \oplus B}</math> or <math>A \odot B</math>. <br /><br />
Distinctive Shape: [[File:XNOR distinctive logic gate.png]]<br />
<br />
[http://en.wikipedia.org/wiki/Logic_gate Information Source]<br />
<br />
==Resources==<br />
<br />
The rest of the "episodes" on circuitry, as well as circuit worksheets, can be found [[Circuit Lab (Episodes)|here]].<br />
The rules for a trial event form on Ciruit Lab can be found [http://soinc.org/sites/default/files/uploaded_files/trial_events/CircuitLab.pdf here]<br />
<br />
[[Media:SCIENCE OLYMPIAD CIRCUTE LAB MARCH 7TH.pdf| Circuit Lab Notes]]<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Lab Event Pages]]<br />
[[Category:Electricity/Electronics]]</div>
Voltage
https://scioly.org/wiki/index.php?title=File:AND_logic_gate.png&diff=30695
File:AND logic gate.png
2014-04-11T23:04:21Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=Circuit_Lab&diff=30694
Circuit Lab
2014-04-11T23:00:26Z
<p>Voltage: /* Digital Logic */ Added Boolean Algebra</p>
<hr />
<div>{{EventLinksBox<br />
|active=yes<br />
|type=Physics<br />
|cat=Lab<br />
|2009thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=17&t=403 2009]<br />
|2010tests=[http://scioly.org/wiki/2009_Test_Exchange#Shock_Value 2010]<br />
|2010thread=[http://scioly.org/phpBB3/viewtopic.php?f=65&t=1278 2010]<br />
|2011thread=[http://scioly.org/phpBB3/viewtopic.php?f=92&t=2222 2011]<br />
|2011tests=2011<br />
|2013thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=142&t=3691 2013]<br />
|2013tests=2013<br />
|2014thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=166&t=4951 2014]<br />
|2014tests=2014<br />
|2014questions=[http://www.scioly.org/phpBB3/viewtopic.php?f=173&t=5022 2014]<br />
|B Champion=[[Daniel Wright Junior High School]]<br />
|C Champion=[[Harriton High School]]<br />
}}<br />
==Introduction==<br />
Circuit Lab is a laboratory event which deals with the various components and properties of direct current (DC) circuits. Historically, the fields which have been tested in this event are DC circuit concepts and DC circuit analysis (both theory and practice).<br />
<br />
==What is a Circuit?==<br />
Let's take an example of a battery, for now. The battery has a positive (+) end, and a minus ( - ) end. When you touch a wire onto both ends of the battery at the same time, you have created a circuit. (It is generally ill advised to attempt this experiment. Not only will there be nothing to see, but short-circuiting a battery is potentially dangerous). What just happened? Current flowed from one end of the battery to the other through your wire. Therefore, our definition of circuit can simply be a never-ending looped pathway for electrons (the battery counts as a pathway!).<br />
<br />
'''The Requirement of a Closed Conducting Path'''<br />
<br />
There are two requirements which must be met to establish an electric circuit. The first is clearly demonstrated by the above activity. There must be a closed conducting path which extends from the positive terminal to the negative terminal. It is not enough that there is a closed connecting loop; the loop itself must extend from the positive terminal to the negative terminal of the electrochemical cell. An electric circuit is like a water circuit at a water park. The flow of charge through the wires is similar to the flow of water through the pipes and along the slides of the water park. If a pipe gets plugged or broken such that water cannot make a complete path through the circuit, then the flow of water will soon cease. In an electric circuit, all connections must be made and made by conducting materials capable of carrying charge. Metallic materials are conductors and can be inserted into the circuit to successfully light the bulb. There must be a closed conducting loop from the positive to the negative terminal in order to establish a circuit and to have a current.<br />
<br />
==Basic Electrical DC Circuit Theory==<br />
===Current Flow and Direction===<br />
'''"Conventional Current Flow" vs. "Electron Flow"''' - This has to do with how circuit diagrams are interpreted. Now, remember we said that electrons are 'flowing' in the wires? The question here deals with : Do they 'flow' from the positive end of the battery, or the negative end of the battery?<br />
<br />
Just as where in mathematics subtracting a negative is equivalent to adding a negative, so also a flow of positive charges in one direction is the exact same current as a flow of negative charges in the opposite direction. As such in most applications, the choice of current direction is an arbitrary convention.<br />
<br />
Conventional current flow, devised by Benjamin Franklin, views the current as a "flow" of positive charges. Therefore, this concept holds that current "flows" out of the positive end of the battery. Electron flow, on the other hand, deals with the ACTUAL route of the electrons (the primary carrier of electric charge in most circuits). Being negatively charged particles, electron currents moves out of the negative end of the battery.<br />
<br />
===Current===<br />
<br />
What is an "electron?" To put it simply, an electron is an atomic particle which carries a negative charge. These electrons spin around the nucleus of an atom, which has a positive charge, and is located in the very center of the atom. The concept of "electricity" has to do with these electrons and with their "electron flow." Do you remember the example of our battery? This battery takes these negatively charged electrons from a chemical reaction inside the battery, pushes them out of the negative end of the battery, and into the wire. These electrons will then bump electrons in the atoms of the wire over and over until finally electrons arrive back at the positive end of the battery. Elements which allow this process of "bumping" those electrons on over determines how conductive the element is. So, when there's a current, it's just electrons bumping each other from atom to atom and flowing on. The individual electrons generally move very slowly, but the electric current moves at the speed of light.<br />
<br />
<br />
A circuit requires a loop for the electrons to travel on (think of "circle"). This means you can not simply attach a wire to one end of a battery and expect electrons to flow through it. As stated before, in our definition of the circuit, a continuous loop is required. But think about it scientifically: If you did attach the wire to only one end of the battery, where would the electrons go that got bumped to the opposite end of the wire? That is why there needs to be that continuous loop of wire: the electrons need somewhere to go.<br />
<br />
==Voltage, Resistance, and Amperes==<br />
<br />
''For more in-depth information, see [[Circuit Lab (Episodes)|Episode 1]]''<br />
<br />
===Amperes(Symbol I or rarely A)=== <br />
To consider Amps pretend that you are the coach of a baseball team. You want to make your team the best that it can be. There are two ways you can do this, making your team score as much as possible and making the opposing team score as little as possible. Focusing on both would be impossible so naturally you're going to have to choose one area to focus on: say you want to score more runs; let's relate this to the concept of "amperes." The amount of runs you make is your score - the more you get the better your chance of winning. Similarly, amperes measure the amount of current you have flowing per second through an area: is it a lot, or a little bit? Now, if you want to win the game, you don't necessarily have to score a whole lot of runs, you just need to score more than your opponent. So, maybe your resistance to their scoring of runs will be high - and resistance to current flowing is also one of our important terms we need to know. Now, how do these concepts of amperes and resistance relate, straying from the daemons for now? If you multiply the resistance by the amperes, you have the voltage of a circuit (remember, we're always talking about in circuits here, not on a baseball field). This relationship was discovered by Georg Simon Ohm, and it says, simply, that: <br />
<br />
<math>V = I \times R</math> <br />
<br />
Or <br />
<br />
Voltage = Current times Resistance <br />
<br />
*Sometimes E is used in place of V, for electromotive force(EMF), it's the same thing, don't worry.<br />
<br />
[[File:Cool Story.png]]<br />
<br />
===Voltage(V or sometimes E)===<br />
Imagine a battery as a super-soaker, and the water that comes out of it as voltage. The harder you pump that super-soaker, the harder that stream is going to be when it comes out of the gun. Voltage is the potential for that water to go very quickly out of the gun: the more you pumped, putting more "voltage" in, the faster that water will go: but sometimes you will have a "multi-functioning" nozzle which even allows you to adjust that water speed even further. You want the water to go out in a "wider" and "bigger" stream, you might change the nozzle to a bigger opening. What you've just done is changed the amount of space that the water is allowed to go through: the water is now given a much bigger space to flow through. The "voltage," or potential, of the water to go fast and give bruises is still high, but now you've taken away from its hitting-power by spreading it out. Anyone know where I'm going next with this? The bigger your nozzle gets (think of it like the resistance), the smaller the hitting power (current (which is a speed in electricity too!)) is going to be.<br />
<br />
Voltage is technically electrical potential. While in many cases we treat it as an absolute, it is important to remember that in circuits we talk mostly about the difference in voltage, a potential difference, and that things like Ohm's laws only apply to potential ''differences'' not just electrical potential. However, in the context of circuits, Voltage is often used in reference to potential difference.<br />
<br />
=== Resistance(Î©)=== <br />
<br />
A resistor is just a piece of metal, and the piece in the center there is what provides the resistance.<br />
<br />
And as for what resistance is itself - it is the force against the flow of the electrons. They transform the electrical energy they absorb into heat energy.<br />
<br />
Imagine our electrons - flowing along the wire, pushing new electrons to flow on, and so on. This wire is not very hard to flow in - it's made of a material that's very conductive. But what would happen if we placed something in the middle of the wire that was harder for the electrons to flow through? They're going to be bumping into all the atoms in the material, which will cause the atoms to vibrate. This, in turn, will cause nearby air molecules to take some energy. That energy is in the form of heat. Where did it come from again? From the electrons bumping into atoms inside the resistor. <br />
<br />
===Other Analogy===<br />
The other way that these three are explained is using water as an example. Imagine the basic components of a circuit, a battery, wire, and say, a resistor. In the water analogy, this translates to a pump(because the battery pushes electrons around the circuit), some large pipe(wire), and a section of much smaller pipe(resistor). We know that in the water analogy, the flow rate of the pump is the same as the voltage of the battery, and the pressure in the tubing if the same as the current in the circuit. This is a pretty simple way to explain voltage/current/ and resistance. If we up the voltage, but keep the resistance(pipe size) the same, it logically takes more pressure, however if we keep the flow rate the same and put in large pipes, it takes a lot less pressure to so the same job. Conversely, if we drop the pressure, but keep the same pipe size, the flow rate goes down, and if we maintain constant pressure, but increase the pipe size, the flow rate goes up. And that's all there is to it. Thus we can see the relationships in Ohm's law. Here a fancy picture I didn't make myself.<br />
<br />[[file:Water-electricity.gif|thumb|500px|center|It may help to read the derived units section to understand the units used on the water side.]]<br />
<br />
===Application of Ohm's law===<br />
This section doesn't teach any theory behind Ohm's law, but this is one of the easiest ways to apply the law(or the power law(P=IV), or any similar law). Basically, take a circle and divide into half, then divide one of the halfs in half again(so you have half a circle at the top, and two quarters at the bottom).<br />
Then you put the equation(any equation in the form a=bc), in the case of the power law, P would go into the half, and I and V would go into quarters. Now all you have to do to find a certain value is cover up what you're looking for(for example,finding I using P and V) and look at the 2 uncovered letters, in the example, P and V are uncovered, since P is on top of V, we know that I=P/V, if the letters are next to each other(i.e. finding P from I and V) then you simply multiply. Sure, the math behind it is very simple, but in a competition this method goes a lot quicker than rearranging equations. <br /><br />This is the basic circle[[File:3pie.gif|thumb|300px|center]]<br /><br /><br />Here's another very useful and much more detailed circle.[[File:circuitpie.gif|thumb|300px|center]]<br />
<br />
==Sources==<br />
'''Voltage Sources'''<br />
A voltage source is a theoretical component which outputs a precise, constant voltage regardless of current. There primary usage is in modeling real components. For example, a battery can be modeled as a voltage source in series with a resistor equal to its internal resistance.<br />
<br />
'''Current Source'''<br />
A current source is a theoretical component which outputs a precise, constant current, regardless of the voltage. <br />
<br />
<br />
==Resistors==<br />
<br />
Of course, you didn't think that was all there was to resistors, right? Of course not. <br />
<br />
[[Image:Resistors.JPG|thumb|300px|center|This is a basic Â¼ watt resistor, the actual resistor is the part in between the two silver leads]]<br />
<br />
So what can you do with that... Lots, actually. The color bands around the resistor tell you what the resistance is, and what the tolerance is(how accurate it is). The color codes are: <br />
<br />
{|class="wikitable"<br />
|+Resistor Color Codes<br />
!Color<br />
!Value<br />
|-<br />
|Black<br />
|0<br />
|-<br />
|Brown<br />
|1<br />
|-<br />
|Red<br />
|2<br />
|-<br />
|Orange<br />
|3<br />
|-<br />
|Yellow<br />
|4<br />
|-<br />
|Green<br />
|5<br />
|-<br />
|Blue<br />
|6<br />
|-<br />
|Purple(Indigo)<br />
|7<br />
|-<br />
|Gray<br />
|8<br />
|-<br />
|White<br />
|9<br />
|-<br />
|Gold<br />
|.1<br />
|-<br />
|Silver<br />
|.01<br />
|}<br />
{|class="wikitable"<br />
|+Common Tolerance Codes<br />
!Color<br />
!Percent<br />
|-<br />
|Silver<br />
|10%<br />
|-<br />
|Gold<br />
|5%<br />
|-<br />
|Red<br />
|2%<br />
|-<br />
|Brown<br />
|1%<br />
|}<br />
<br />
By the way, the most common tolerance you will see is Gold, followed by Brown, but this doesn't rule out the possibility. To convert the color codes into resistance values(on a resistor with 3 bands and a tolerance band) read the first two bands off in order(in the picture it would be green, then blue, thus 56) and then multiply that by 10^(color of third band), so the picture would be 56x10^0 which is 56 ohms. If the resistor has more than 4 bands, all you do is read the first howevermany(normally 3) until you only have one color(not tolerance) left, and multiply by 10^last color band. <br />
<br />
===Resistor Networks===<br />
Networks of resistors between two points can be simplified into an equivalent single resistor, for which the resistance can be calculated according to the configuration and values of the resistors within the network.<br />
<br />
====Series Resistance====<br />
The resistance of a resistor is directly proportional to the length of the resistive material. As such, because placing resistors in series effectively adds the lengths, resistances add in series. Therefore, for a chain of resistors, the equivalent resistance is equal to the sum of individual resistors.<br />
<br />
====Parallel Resistance====<br />
In parallel, it is not the resistances that add, but the conductances. An analogy for this is to imagine a crowd of people trying to get through a door. A single door will allow so many people per minute, but if a second, adjacent, identical door is opened, the same number of people per minute will simultaneously move through that door. Therefore, twice the number of people will move through the doors per minute. Similarly, two identical resistors in parallel will conduct twice the current as a single one. Therefore the total conductance is equal to the sum of individual conductances in parallel. As conductance is the reciprocal of resistance, the usual formula is that 1/Rt=1/R1+1/R2+...+1/Rn for n resistors in parallel.<br />
<br />
''''Networks Containing Both Series and Parallel'''<br />
Many real circuits will contain a combination of both series and parallel components. To simplify these networks, one must find parts of the networks that are purely one or the other and simplify them according to the formulas above. One can repeat this process until the network is simplified into a single equivalent resistor.<br />
<br />
===Wheatstone Bridge===<br />
A wheatstone bridge is used to measure an unknown resistance value to a high degree of accuracy. It uses 4 resistors set up in a diamond fashion(shown below) and a voltmeter. In the schematic below, Rx is the unkown resistance, R1 and R3 are fixed resistance values(generally the same, but they don't have to be the same, also generally >1% tolerance, but again, not always) and R2 is a variable resistor(potentiometer, this is not always the case, see below). By adjusting R2 until the voltmeter reads 0 volts, you know that the ratio between the R1/R2 and R3/Rx is equal.<br /><br /><br />
[[file:500px-Wheatstonebridge.svg.png|thumb|300px|center|Wheatstone Bridge Schematic(Courtesy Wikipedia)]]<br /><br /><br />
To understand this, think of a circuit with two resistors of equal value in series, connected to a +5v source, becuase the resistances are equal, the voltage droop is equal, this kind of circuit is called a voltage divider, becuase the voltage in between the two resistors is 1/2 the input voltage. Again, imagine a circuit with 2 resistors in series connected to a +5v source, however this time, the resistors are 50 ohms and 25 ohms, becuase the total resistence (remember series resistance?) is 75 ohms, at 5v, we can calculate the current, and from there calculate the voltage drop from each resistor, you should have gotten 3.33 volts across the first, and 1.66 for the second one (I tried to pick better numbers, honest!); well, the voltage happens to be in the same ratio as the resistance values; now that we've proved that, we can apply it to the wheatstone bridge.<br /><br /><br />
With that in mind, we now know that the ratio of the resistors is what controls the voltage at the midpoint, so if two sets of resistors have the same ratio, then they would have the same voltage, see where I'm going? When the voltage across the bridge is 0, the sets of resistors(R1/R2 and R3/Rx) have the same voltage, and thus the same ratio of resistance values! Since we know the ratio of the first leg(R1/R2, remember we set R2 to a known value to balance the bridge...) and we know R3, it's fairly simple to solve for Rx.<br /><br /><br />
Now here's the fun part... What if you don't want to have to change R2? Well then, you can, using the same principle, take the voltage across the bridge, and calculate Rx from that... I'll leave out the derivation (Hey, it'd make good practice!), but basically, by applying all the concepts discussed here (Kirchhoff's laws, Ohm's law, etc) you end up at the equation <br /> <math>V_G = ({R_x \over {R_3 + R_x}} - {R_2 \over {R_1 + R_2}})</math><br />
<br />
==Kirchhoff's Laws==<br />
Kirchhoff has two well-known laws of circuits: '''Kirchhoff's Current Law''' (KCL) and '''Kirchhoff's Voltage Law''' (KVL). They are simplifications of Maxwell's Laws of Electromagnetism that are valid for most practical circuits.<br />
<br />
<br />
===Kirchhoff's Current Law===<br />
A '''node''' is a junction in a circuit where two or more electrical components meet. '''Kirchhoff's Current Law''' states that sum of currents entering a node is equal to the sum of currents leaving the node. This is based on the assumption that charges cannot accumulate in a node of the circuit. Equivalently, if one designates the direction of the currents with a sign (eg all currents leaving the node are negative), the sum of currents at each node equals zero.<br />
<br />
====Node Method====<br />
The '''Node Method''' is a powerful tool of circuit analysis that is based upon Kirchhoff's Current Law. Basically, one writes the equation for every node in the circuit based upon unknown variables. Then from the resultant system of equations, one can calculate all the unknown variables and solve the circuit. It is often unnecessary for simple circuits, but becomes quite convenient for large circuits.<br />
<br />
'''Detailed method:'''<br><br />
1. Select a node to be your '''ground''' and assign it a voltage of zero. (N.B. The term "ground" in the context of circuit analysis does not necessarily mean that it is connected to the ground. Instead, it is a node designated at zero electrical potential from which all other voltages are measures.)<br><br />
2. Assign every other node in the circuit a variable voltage. You may in certain cases be able to calculate a voltage for a few nodes (e.g. if the negative terminal of the battery is connected to the ground, the node connected to the positive terminal will have a known, positive voltage).<br><br />
3. Write the KCL equation for every node in the equation. [Example soon].<br><br />
4. Solve the resulting system of equations for all the unknown variables.<br />
At this point, you know the voltage for every node in the circuit and should be able to easily calculate anything else.<br />
<br />
===Kirchhoff's Voltage Law===<br />
'''Kirchhoff's Voltage Law''' (KVL) states that for any closed loop in a circuit, the sum of voltages will be zero. One must be very careful with sign convention for this to work. For example, in a simple series circuit of resistors and voltage sources, one must choose either the voltage sources or the resistors to have negative voltages. This is based on the assumption that there is no changing magnetic field.<br />
<br />
====Mesh Method====<br />
The '''Mesh Method''' is another technique of circuit analysis based upon Kirchhoff's Voltage Law. Essentially, one designates a variable for a current circulating through every loop in the circuit, and then writes an equation for each of these in terms of KVL.<br />
<br />
<br />
<br />
==Equivalent circuits==<br />
Just as networks of individual resistors can be simplified into a single equivalent resistor, so also can more complicated networks. Any network containing resistors, current sources, and voltage sources can be transformed into a Thevenin or Norton equivalent. This is especially useful when analyzing circuits containing other components, as the entire rest of the circuit around the component may be a network which has an equivalent.<br />
===Thevenin equivalent===<br />
The Thevenin equivalent circuit between two points consists of a voltage source in series with a resistor. In order to find the Thevenin voltage, you must find the open-circuit voltage across the two points (ie when it is broken open). The resistance is found by removing all the power sources (replacing current sources with shorts and voltage sources with breaks) and finding the equivalent resistance of the resultant resistor network.<br />
<br />
===Norton equivalent===<br />
The network can also be represented by a Norton equivalent. It consists of a resistor in parallel with a current source. The Norton resistance is equal to the Thevenin resistance. The Norton equivalent current is equal to the current that passes between the two points if you short circuit them.<br />
<br />
==Other Topics==<br />
===Capacitors===<br />
Capacitors are, in DC at least, a device that stores a charge. When capacitors are in a circuit, they are said to resist change in voltage(i.e. if the voltage in a circuit goes up, the capacitor charges, taking away the excess voltage. If the voltage drops, the capacitor discharges, adding back to the circuit to make up the difference. There are many types of capacitors(Mylar, polystyrene, electrolytic, etc), but they all do the same basic job. At the most basic level, a capacitor is comprised of two plates separated by a dielectric(insulting material) that stores a charge, there's a few basic concepts it may be helpful to know. First off, look at the charging circuit below, the capacitor is uncharged in the beginning, but when the switch is closed, it begins to charge, as it starts to charge, the resistance across it is small(thus a current flows through the circuit, charging the capacitor), however as the voltage of the capacitor reaches <math>V_0</math>, the current decays exponentially, because the voltage is smaller, less current flows(remember?). This can also be shown by trying to measure the resistance of a capacitor(see below, because the meter puts out a small current, that charges the capacitor). Its useful to in some cases calculate the voltage for a capacitor as it is charging or discharging, for which 2 formulas are incredibly helpful. For a charging capacitor in an RC circuit Vc = Vo(1-e^(-t/(RC))) and for a discharging one, Vc = Vo(e^(-t/(RC))).<br />[[file:CapCharging.png|thumb|300px|center|Charging circuit, from wikipedia]]<br />
<br />
'''Other Analogy'''<br /><br />
In the water analogy, a capacitor is simulated as a piece of rubber blocking the pipe. Using this example, we can see that a DC current would flow for a time, but when the rubber reached it's elastic limit, it would stop, the same as the capacitor charge curve discussed above. However, an AC current(imagine the water moving back and forth very fast) would simply move the rubber back and forth, never stopping the rubber on the other side from flowing(this is true for electricity, but in an effort to not drone on to long, it's not in there).<br />
<br />
===Inductors===<br />
An inductor is basically an electromagnet, however it exhibits special characteristics in a circuit. In the most simple terms, it's the opposite of a capacitor, however this is slightly misleading. An inductor has an ability to store a charge in a magnetic field(whereas a capacitor stores it in an electric field) and has the ability to maintain a constant current in a circuit(whereas a capacitor can maintain a constant voltage). This means that an inductor can easily conduct DC(whereas a capacitor can easily conduct AC), however if AC is put through an inductor, the magnetic field will grow and collapse with the rise and fall of current, which tends to oppose the flow of AC through an inductor.<br />
<br />
'''Other Analogy'''<br />
In the water analogy, an inductor is a waterwheel, with a constant flow of water through it, the waterwheel spins, and all is fine, however with an alternating flow, the water wheel is continuously trying to turn back and forth, limiting the flow of water.<br />
===Diodes===<br />
Don't let anything in here scare you, you probably only really need to know that a diode conducts only in one way, but hey, it never hurts to know more, right?<br />
This is a topic that's not covered very deeply in the rules, so I will only go over the basics in here. A diode is a semiconductor made of a junction of P-type and N-type silicon(don't worry to much about the details), it's special in that it only conducts in one direction. There are a lot of different types of diodes(schottky, zener, light emmitting diodes) they all vary in a few charecteristics, mainly, their forward voltage drop(how much voltage is lost while conducting), and avalanche voltage(point at which they coduct in reverse), for example, schottky diodes are used in power supplies when you need to combine two power supplies of the same voltage(so one doesn't backfeed the other) because of their charecteristcally low forward voltage drop, whereas zener diodes are used in applications where one needs to detect when a voltage is above a certain point becuase of their low avalanche voltage(put on in backwards and you'll only get a voltage on the other side of it when it crosses a certain point), light emmitting diodes are used... well... you should be able to figure that one out. The arrow on the symbol of a diode points the direction of the conventional (positive) current through the diode.<br /><br /><br />
'''Other Analogy'''<br />
In the water analogy, the diode is simply a check-valve(one way valve). That's it, nothing more to it.<br />
====Circuit Analysis with Ideal Diodes====<br />
Ideal diodes can generally be approximated by either a short or a break in the circuit. Generally to analyze a circuit with an ideal diode, one will make an educated guess on whether or not the diode will conduct. Once one finds a solution for this hypothesized circuit, one much check whether it makes sense. If you assumed the diode would conduct, you must make sure it is conducting current in the correct direction. If you assumed it does not conduct, you must check to make sure the voltage across the hypothetically non-conducting diode is such that it would not conduct. If this is not the case, you must switch your assumption and recalculate the circuit.<br />
<br />
===Base and Derived Units===<br />
SI base units are the base quantities that are independent. There is a total of seven units, but the ones important to this event are meters (m, length), kilograms (kg, mass), amperes (A, electric current), and seconds (s, time). Derived units are units that come from a combination of the base units. The ones important to this event are newtons, joules, watts, coulombs, volts, farads, siemens, and ohms. The table below shows how each of the units is related. <br />
<br />
{|class="wikitable"<br />
|+Derived Units<br />
!Quantity measured<br />
!Unit name<br />
!Unit symbol<br />
!Expression in other SI Units<br />
!Base SI Units<br />
|-<br />
|Electrostatic Force<br />
|Newton<br />
|N<br />
| -<br />
|kg*m*s<sup>-2</sup><br />
|-<br />
|Energy, work<br />
|Joule<br />
|J<br />
|N*m<br />
|m<sup>2</sup>*kg*s<sup>-2</sup><br />
|-<br />
|Power<br />
|Watt<br />
|W<br />
|J/s<br />
|m<sup>2</sup>*kg*s<sup>-3</sup><br />
|-<br />
|Electric Charge<br />
|Coulomb<br />
|C<br />
| - <br />
|s*A<br />
|-<br />
|Electric Potential Difference<br />
|Volt<br />
|V<br />
|W/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-1</sup><br />
|-<br />
|Capacitance<br />
|Farad<br />
|F<br />
|C/V<br />
|s<sup>4</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|Electric Resistance<br />
|Ohm<br />
|Î©<br />
|V/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-2</sup><br />
|-<br />
|Electric Conductance<br />
|Sieman<br />
|S<br />
|A/V<br />
|s<sup>3</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|}<br />
<br />
Another important derived quantity that does not have a special unit name is the electric field strength, measured in V/m.<br><br />
One coulomb is also equal to the charge of 6.24 x 10<sup>18</sup> electrons.<br />
<br />
===Meters===<br />
[[file:Meter.JPG|thumb|300px|center|This is a fairly complex Fluke 287 multimeter, note the separate jacks for measuring current.]]<br />
<br />
During the event, the test may require you to measure certain values in a circuit, for this you can use either a multimeter or probes(whatever the ES gives you), but you have to know how to hook it up, or you could get yourself dq'd(I've seen this happen). Basically, there are three things that you could be asked to measure, voltage, current, or resistance. <br /><br /><br />
'''Voltage''' is fairly straightforward, you put the said device in voltage mode(make sure the probes are hooked up in the right place!) and put them across whatever you want to measure and it reads off a voltage(the difference in potential between the probes, the meter has a high enough resistance(called impedance) that it won't cause any significant amount of current to flow(most meters are around 11 million ohms!)). <br /><br /><br />
'''Current''' is another one you might be asked to measure, think of current as the flow-rate in the water analogy, to measure the flow, you have to 'get into' the circuit, this is why meters have a separate jack for current, there's a fuse in between the current jack and the common, and a low value(<5 ohms), by connecting the leads to the circuit, you allow current to flow with minimal resistance. The resistor in the circuit is called a shunt(that's just a big term for a resistor used to measure current) and by measuring the voltage across it, you can calculate the current(because the resistor has a constant value). Never put a meter set up to measure current in parallel with part of the circuit. You might blow a fuse in the meter or worse.<br /><br /><br />
'''Resistance''' is a little trickier, it can help to understand how the meter's going to measure it, basically, it puts out a small voltage(~2-3v) and measures the current that flows in the circuit, and calculates the resistance. This means that you can't measure resistance with power on the circuit, and you have to account for all the possible paths, not just the most direct route. Generally, one must first disconnect a component from the circuit before measuring the resistance. Never put an external voltage across a meter in resistance mode, as this could damage the meter.<br />
<br />
===AC Power===<br />
For more info, see [[AC Power|this page]].<br /><br/><br />
Up until now, the entire discussion(minus a mention when talking about capacitors) has dealt with DC, or direct current. In a DC circuit, current flows from the positive to the negative terminals of a battery or other source, that it(electrons flow the opposite, see above). However, the power in your house is AC, not DC(unless you live in a very strange house), AC, or alternating current, is a much more complicated beast. Basically, the direction of the current flow change, if you plotted voltage vs time, instead of a line, for DC, you would get a sine wave. This yields many advantages, namely, the use of transformers for voltage step-up/step-down. <br /><br /><br />
'''Transformers'''<br /><br />
Transformers are basically 2 electromagnets that are put together, most of the time sharing a common core of iron. Transformers work because the AC generates a constantly changing magnetic field in the primary coil, which can induce a charge in the secondary coil. It isn't possible to build a DC transformer because the magnetic field would be constant, remember that stable magnetic fields(stationary) can't induce a charge.(a changing field acts the same as a moving one). The ratio of the turns of the primary winding to the turns of the secondary is equal to the ratio of the primary voltage to the secondary(i.e. 2 turns on the primary and 1 on the secondary will half the primary voltage)<br />
<br />
===Digital Logic===<br />
<br />
In digital logic in circuits, a current corresponds to a "true" or "1", and no or very little current corresponds to a "false" or "0". A '''logic gate''' will take 1 or more of these signals, perform a logical operation on it, and then either send a true or a false on its way.<br />
<br />
A simple example of a logic gate is a transistor. If it receives very little current (false/0), then it does not allow current to pass through it (false/0). If it receives a current (true/1), then it allows current to pass through it (true/1).<br />
<br />
Here is a list of logic gates:<br />
*'''AND''' AND must have two trues in order for current to pass through it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A AND B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>A \cdot B</math> or <math>A</math> & <math>B</math>.<br />
<br />
*'''OR''' OR will allow current to pass through it if any true is given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A OR B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>A+B</math>.<br />
<br />
*'''NOT''' NOT turns trues into falses and falses into trues. The NOT gate is commonly called an inverter.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!NOT A<br />
|-<br />
|0<br />
|1<br />
|-<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline A</math> or ~<math>A</math>.<br />
<br />
*'''NAND''' NAND blocks current only when two trues are given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NAND B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A \cdot B}</math> or <math>A | B</math>.<br />
<br />
*'''NOR''' NOR only allows current to pass through it when it is given two falses.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NOR B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A + B}</math> or <math>A - B</math>.<br />
<br />
*'''XOR''' XOR only allows current to pass through it when the two signals it is sent are not the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XOR B<br />
|-<br />
|0<br />
|0<br />
|0<br />
|-<br />
|0<br />
|1<br />
|1<br />
|-<br />
|1<br />
|0<br />
|1<br />
|-<br />
|1<br />
|1<br />
|0<br />
|-<br />
|}<br />
Boolean Algebra: <math>A \oplus B</math>.<br />
<br />
*'''XNOR''' XNOR only allows current to pass through it when the two signals it is sent are the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!colspan="2"| INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XNOR B<br />
|-<br />
|0<br />
|0<br />
|1<br />
|-<br />
|0<br />
|1<br />
|0<br />
|-<br />
|1<br />
|0<br />
|0<br />
|-<br />
|1<br />
|1<br />
|1<br />
|-<br />
|}<br />
Boolean Algebra: <math>\overline {A \oplus B}</math> or <math>A \odot B</math>.<br />
<br />
[http://en.wikipedia.org/wiki/Logic_gate Information Source]<br />
<br />
==Resources==<br />
<br />
The rest of the "episodes" on circuitry, as well as circuit worksheets, can be found [[Circuit Lab (Episodes)|here]].<br />
The rules for a trial event form on Ciruit Lab can be found [http://soinc.org/sites/default/files/uploaded_files/trial_events/CircuitLab.pdf here]<br />
<br />
[[Media:SCIENCE OLYMPIAD CIRCUTE LAB MARCH 7TH.pdf| Circuit Lab Notes]]<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Lab Event Pages]]<br />
[[Category:Electricity/Electronics]]</div>
Voltage
https://scioly.org/wiki/index.php?title=User:Voltage&diff=30693
User:Voltage
2014-04-11T22:40:36Z
<p>Voltage: </p>
<hr />
<div>Hi. I'm from [[Pilgrimage Homeschool]] Division B.<br />
<br />
Thanks for checking out my user page.<br />
<br />
Voltage's Avatar:<br />
<br />
[[File:Voltage's Avatar 1.jpeg]]<br />
<br />
==My Events==<br />
<br />
Here's a list of my past and current events.<br />
<br />
2012-2013 <br /><br />
(Regional/State) (placings in AA league, not overall) <br /><br />
Disease Detectives (2/2) <br /><br />
Road Scholar (1/1) <br /><br />
Experimental Design (2/1) <br /><br />
<br />
2013-2014 <br /><br />
(Regional/State/National) (placings in AA league, not overall) <br /><br />
Disease Detectives (3/1/?) <br /><br />
Road Scholar (1/1/?) <br /><br />
Experimental Design (1/1/?) <br /><br />
Simple Machines (1/1/?) <br /><br />
Shock Value (1/1/?) <br /><br />
Metric Mastery (4/1/?) <br /><br />
<br />
[[Category:User Pages]]</div>
Voltage
https://scioly.org/wiki/index.php?title=File:Voltage%27s_Avatar_1.jpeg&diff=30692
File:Voltage's Avatar 1.jpeg
2014-04-11T22:34:28Z
<p>Voltage: </p>
<hr />
<div></div>
Voltage
https://scioly.org/wiki/index.php?title=User:Voltage&diff=30691
User:Voltage
2014-04-11T22:33:11Z
<p>Voltage: Adding my avatar</p>
<hr />
<div>Hi. I'm from [[Pilgrimage Homeschool]] Division B.<br />
<br />
Thanks for checking out my user page.<br />
<br />
[[File:Voltage's Avatar 1.jpeg]]<br />
<br />
==My Events==<br />
<br />
Here's a list of my past and current events.<br />
<br />
2012-2013 <br /><br />
(Regional/State) (placings in AA league, not overall) <br /><br />
Disease Detectives (2/2) <br /><br />
Road Scholar (1/1) <br /><br />
Experimental Design (2/1) <br /><br />
<br />
2013-2014 <br /><br />
(Regional/State/National) (placings in AA league, not overall) <br /><br />
Disease Detectives (3/1/?) <br /><br />
Road Scholar (1/1/?) <br /><br />
Experimental Design (1/1/?) <br /><br />
Simple Machines (1/1/?) <br /><br />
Shock Value (1/1/?) <br /><br />
Metric Mastery (4/1/?) <br /><br />
<br />
[[Category:User Pages]]</div>
Voltage
https://scioly.org/wiki/index.php?title=User:Asthedeer&diff=30673
User:Asthedeer
2014-04-11T11:18:19Z
<p>Voltage: Just categorizing :)</p>
<hr />
<div>Hi! I'm asthedeer from [[Pilgrimage Homeschool]] !<br />
<br />
This year, I am in Rocks and Minerals, Helicopters, and Can't Judge a Powder. I want to do Heredity when our team goes to nationals, but it conflicts with R&M :(. <br />
<br />
Medal count (Regionals/States/Nationals)<br />
R&M: 2/1/?<br />
Helicopters: 2/1/?<br />
CJAP: 2/1/?<br />
<br />
Excited for Nationals!<br />
<br />
[[Category:User Pages]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Circuit_Lab&diff=30657
Circuit Lab
2014-04-10T11:42:49Z
<p>Voltage: /* Digital Logic */ Pictures still need to be added</p>
<hr />
<div>{{EventLinksBox<br />
|active=yes<br />
|type=Physics<br />
|cat=Lab<br />
|2009thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=17&t=403 2009]<br />
|2010tests=[http://scioly.org/wiki/2009_Test_Exchange#Shock_Value 2010]<br />
|2010thread=[http://scioly.org/phpBB3/viewtopic.php?f=65&t=1278 2010]<br />
|2011thread=[http://scioly.org/phpBB3/viewtopic.php?f=92&t=2222 2011]<br />
|2011tests=2011<br />
|2013thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=142&t=3691 2013]<br />
|2013tests=2013<br />
|2014thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=166&t=4951 2014]<br />
|2014tests=2014<br />
|2014questions=[http://www.scioly.org/phpBB3/viewtopic.php?f=173&t=5022 2014]<br />
|B Champion=[[Daniel Wright Junior High School]]<br />
|C Champion=[[Harriton High School]]<br />
}}<br />
==Introduction==<br />
Circuit Lab is a laboratory event which deals with the various components and properties of direct current (DC) circuits. Historically, the fields which have been tested in this event are DC circuit concepts and DC circuit analysis (both theory and practice).<br />
<br />
==What is a Circuit?==<br />
Let's take an example of a battery, for now. The battery has a positive (+) end, and a minus ( - ) end. When you touch a wire onto both ends of the battery at the same time, you have created a circuit. (It is generally ill advised to attempt this experiment. Not only will there be nothing to see, but short-circuiting a battery is potentially dangerous). What just happened? Current flowed from one end of the battery to the other through your wire. Therefore, our definition of circuit can simply be a never-ending looped pathway for electrons (the battery counts as a pathway!).<br />
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'''The Requirement of a Closed Conducting Path'''<br />
<br />
There are two requirements which must be met to establish an electric circuit. The first is clearly demonstrated by the above activity. There must be a closed conducting path which extends from the positive terminal to the negative terminal. It is not enough that there is a closed connecting loop; the loop itself must extend from the positive terminal to the negative terminal of the electrochemical cell. An electric circuit is like a water circuit at a water park. The flow of charge through the wires is similar to the flow of water through the pipes and along the slides of the water park. If a pipe gets plugged or broken such that water cannot make a complete path through the circuit, then the flow of water will soon cease. In an electric circuit, all connections must be made and made by conducting materials capable of carrying charge. Metallic materials are conductors and can be inserted into the circuit to successfully light the bulb. There must be a closed conducting loop from the positive to the negative terminal in order to establish a circuit and to have a current.<br />
<br />
==Basic Electrical DC Circuit Theory==<br />
===Current Flow and Direction===<br />
'''"Conventional Current Flow" vs. "Electron Flow"''' - This has to do with how circuit diagrams are interpreted. Now, remember we said that electrons are 'flowing' in the wires? The question here deals with : Do they 'flow' from the positive end of the battery, or the negative end of the battery?<br />
<br />
Just as where in mathematics subtracting a negative is equivalent to adding a negative, so also a flow of positive charges in one direction is the exact same current as a flow of negative charges in the opposite direction. As such in most applications, the choice of current direction is an arbitrary convention.<br />
<br />
Conventional current flow, devised by Benjamin Franklin, views the current as a "flow" of positive charges. Therefore, this concept holds that current "flows" out of the positive end of the battery. Electron flow, on the other hand, deals with the ACTUAL route of the electrons (the primary carrier of electric charge in most circuits). Being negatively charged particles, electron currents moves out of the negative end of the battery.<br />
<br />
===Current===<br />
<br />
What is an "electron?" To put it simply, an electron is an atomic particle which carries a negative charge. These electrons spin around the nucleus of an atom, which has a positive charge, and is located in the very center of the atom. The concept of "electricity" has to do with these electrons and with their "electron flow." Do you remember the example of our battery? This battery takes these negatively charged electrons from a chemical reaction inside the battery, pushes them out of the negative end of the battery, and into the wire. These electrons will then bump electrons in the atoms of the wire over and over until finally electrons arrive back at the positive end of the battery. Elements which allow this process of "bumping" those electrons on over determines how conductive the element is. So, when there's a current, it's just electrons bumping each other from atom to atom and flowing on. The individual electrons generally move very slowly, but the electric current moves at the speed of light.<br />
<br />
<br />
A circuit requires a loop for the electrons to travel on (think of "circle"). This means you can not simply attach a wire to one end of a battery and expect electrons to flow through it. As stated before, in our definition of the circuit, a continuous loop is required. But think about it scientifically: If you did attach the wire to only one end of the battery, where would the electrons go that got bumped to the opposite end of the wire? That is why there needs to be that continuous loop of wire: the electrons need somewhere to go.<br />
<br />
==Voltage, Resistance, and Amperes==<br />
<br />
''For more in-depth information, see [[Circuit Lab (Episodes)|Episode 1]]''<br />
<br />
===Amperes(Symbol I or rarely A)=== <br />
To consider Amps pretend that you are the coach of a baseball team. You want to make your team the best that it can be. There are two ways you can do this, making your team score as much as possible and making the opposing team score as little as possible. Focusing on both would be impossible so naturally you're going to have to choose one area to focus on: say you want to score more runs; let's relate this to the concept of "amperes." The amount of runs you make is your score - the more you get the better your chance of winning. Similarly, amperes measure the amount of current you have flowing per second through an area: is it a lot, or a little bit? Now, if you want to win the game, you don't necessarily have to score a whole lot of runs, you just need to score more than your opponent. So, maybe your resistance to their scoring of runs will be high - and resistance to current flowing is also one of our important terms we need to know. Now, how do these concepts of amperes and resistance relate, straying from the daemons for now? If you multiply the resistance by the amperes, you have the voltage of a circuit (remember, we're always talking about in circuits here, not on a baseball field). This relationship was discovered by Georg Simon Ohm, and it says, simply, that: <br />
<br />
<math>V = I \times R</math> <br />
<br />
Or <br />
<br />
Voltage = Current times Resistance <br />
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*Sometimes E is used in place of V, for electromotive force(EMF), it's the same thing, don't worry.<br />
<br />
[[File:Cool Story.png]]<br />
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===Voltage(V or sometimes E)===<br />
Imagine a battery as a super-soaker, and the water that comes out of it as voltage. The harder you pump that super-soaker, the harder that stream is going to be when it comes out of the gun. Voltage is the potential for that water to go very quickly out of the gun: the more you pumped, putting more "voltage" in, the faster that water will go: but sometimes you will have a "multi-functioning" nozzle which even allows you to adjust that water speed even further. You want the water to go out in a "wider" and "bigger" stream, you might change the nozzle to a bigger opening. What you've just done is changed the amount of space that the water is allowed to go through: the water is now given a much bigger space to flow through. The "voltage," or potential, of the water to go fast and give bruises is still high, but now you've taken away from its hitting-power by spreading it out. Anyone know where I'm going next with this? The bigger your nozzle gets (think of it like the resistance), the smaller the hitting power (current (which is a speed in electricity too!)) is going to be.<br />
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Voltage is technically electrical potential. While in many cases we treat it as an absolute, it is important to remember that in circuits we talk mostly about the difference in voltage, a potential difference, and that things like Ohm's laws only apply to potential ''differences'' not just electrical potential. However, in the context of circuits, Voltage is often used in reference to potential difference.<br />
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=== Resistance(Î©)=== <br />
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A resistor is just a piece of metal, and the piece in the center there is what provides the resistance.<br />
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And as for what resistance is itself - it is the force against the flow of the electrons. They transform the electrical energy they absorb into heat energy.<br />
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Imagine our electrons - flowing along the wire, pushing new electrons to flow on, and so on. This wire is not very hard to flow in - it's made of a material that's very conductive. But what would happen if we placed something in the middle of the wire that was harder for the electrons to flow through? They're going to be bumping into all the atoms in the material, which will cause the atoms to vibrate. This, in turn, will cause nearby air molecules to take some energy. That energy is in the form of heat. Where did it come from again? From the electrons bumping into atoms inside the resistor. <br />
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===Other Analogy===<br />
The other way that these three are explained is using water as an example. Imagine the basic components of a circuit, a battery, wire, and say, a resistor. In the water analogy, this translates to a pump(because the battery pushes electrons around the circuit), some large pipe(wire), and a section of much smaller pipe(resistor). We know that in the water analogy, the flow rate of the pump is the same as the voltage of the battery, and the pressure in the tubing if the same as the current in the circuit. This is a pretty simple way to explain voltage/current/ and resistance. If we up the voltage, but keep the resistance(pipe size) the same, it logically takes more pressure, however if we keep the flow rate the same and put in large pipes, it takes a lot less pressure to so the same job. Conversely, if we drop the pressure, but keep the same pipe size, the flow rate goes down, and if we maintain constant pressure, but increase the pipe size, the flow rate goes up. And that's all there is to it. Thus we can see the relationships in Ohm's law. Here a fancy picture I didn't make myself.<br />
<br />[[file:Water-electricity.gif|thumb|500px|center|It may help to read the derived units section to understand the units used on the water side.]]<br />
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===Application of Ohm's law===<br />
This section doesn't teach any theory behind Ohm's law, but this is one of the easiest ways to apply the law(or the power law(P=IV), or any similar law). Basically, take a circle and divide into half, then divide one of the halfs in half again(so you have half a circle at the top, and two quarters at the bottom).<br />
Then you put the equation(any equation in the form a=bc), in the case of the power law, P would go into the half, and I and V would go into quarters. Now all you have to do to find a certain value is cover up what you're looking for(for example,finding I using P and V) and look at the 2 uncovered letters, in the example, P and V are uncovered, since P is on top of V, we know that I=P/V, if the letters are next to each other(i.e. finding P from I and V) then you simply multiply. Sure, the math behind it is very simple, but in a competition this method goes a lot quicker than rearranging equations. <br /><br />This is the basic circle[[File:3pie.gif|thumb|300px|center]]<br /><br /><br />Here's another very useful and much more detailed circle.[[File:circuitpie.gif|thumb|300px|center]]<br />
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==Sources==<br />
'''Voltage Sources'''<br />
A voltage source is a theoretical component which outputs a precise, constant voltage regardless of current. There primary usage is in modeling real components. For example, a battery can be modeled as a voltage source in series with a resistor equal to its internal resistance.<br />
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'''Current Source'''<br />
A current source is a theoretical component which outputs a precise, constant current, regardless of the voltage. <br />
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==Resistors==<br />
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Of course, you didn't think that was all there was to resistors, right? Of course not. <br />
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[[Image:Resistors.JPG|thumb|300px|center|This is a basic Â¼ watt resistor, the actual resistor is the part in between the two silver leads]]<br />
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So what can you do with that... Lots, actually. The color bands around the resistor tell you what the resistance is, and what the tolerance is(how accurate it is). The color codes are: <br />
<br />
{|class="wikitable"<br />
|+Resistor Color Codes<br />
!Color<br />
!Value<br />
|-<br />
|Black<br />
|0<br />
|-<br />
|Brown<br />
|1<br />
|-<br />
|Red<br />
|2<br />
|-<br />
|Orange<br />
|3<br />
|-<br />
|Yellow<br />
|4<br />
|-<br />
|Green<br />
|5<br />
|-<br />
|Blue<br />
|6<br />
|-<br />
|Purple(Indigo)<br />
|7<br />
|-<br />
|Gray<br />
|8<br />
|-<br />
|White<br />
|9<br />
|-<br />
|Gold<br />
|.1<br />
|-<br />
|Silver<br />
|.01<br />
|}<br />
{|class="wikitable"<br />
|+Common Tolerance Codes<br />
!Color<br />
!Percent<br />
|-<br />
|Silver<br />
|10%<br />
|-<br />
|Gold<br />
|5%<br />
|-<br />
|Red<br />
|2%<br />
|-<br />
|Brown<br />
|1%<br />
|}<br />
<br />
By the way, the most common tolerance you will see is Gold, followed by Brown, but this doesn't rule out the possibility. To convert the color codes into resistance values(on a resistor with 3 bands and a tolerance band) read the first two bands off in order(in the picture it would be green, then blue, thus 56) and then multiply that by 10^(color of third band), so the picture would be 56x10^0 which is 56 ohms. If the resistor has more than 4 bands, all you do is read the first howevermany(normally 3) until you only have one color(not tolerance) left, and multiply by 10^last color band. <br />
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===Resistor Networks===<br />
Networks of resistors between two points can be simplified into an equivalent single resistor, for which the resistance can be calculated according to the configuration and values of the resistors within the network.<br />
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====Series Resistance====<br />
The resistance of a resistor is directly proportional to the length of the resistive material. As such, because placing resistors in series effectively adds the lengths, resistances add in series. Therefore, for a chain of resistors, the equivalent resistance is equal to the sum of individual resistors.<br />
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====Parallel Resistance====<br />
In parallel, it is not the resistances that add, but the conductances. An analogy for this is to imagine a crowd of people trying to get through a door. A single door will allow so many people per minute, but if a second, adjacent, identical door is opened, the same number of people per minute will simultaneously move through that door. Therefore, twice the number of people will move through the doors per minute. Similarly, two identical resistors in parallel will conduct twice the current as a single one. Therefore the total conductance is equal to the sum of individual conductances in parallel. As conductance is the reciprocal of resistance, the usual formula is that 1/Rt=1/R1+1/R2+...+1/Rn for n resistors in parallel.<br />
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''''Networks Containing Both Series and Parallel'''<br />
Many real circuits will contain a combination of both series and parallel components. To simplify these networks, one must find parts of the networks that are purely one or the other and simplify them according to the formulas above. One can repeat this process until the network is simplified into a single equivalent resistor.<br />
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===Wheatstone Bridge===<br />
A wheatstone bridge is used to measure an unknown resistance value to a high degree of accuracy. It uses 4 resistors set up in a diamond fashion(shown below) and a voltmeter. In the schematic below, Rx is the unkown resistance, R1 and R3 are fixed resistance values(generally the same, but they don't have to be the same, also generally >1% tolerance, but again, not always) and R2 is a variable resistor(potentiometer, this is not always the case, see below). By adjusting R2 until the voltmeter reads 0 volts, you know that the ratio between the R1/R2 and R3/Rx is equal.<br /><br /><br />
[[file:500px-Wheatstonebridge.svg.png|thumb|300px|center|Wheatstone Bridge Schematic(Courtesy Wikipedia)]]<br /><br /><br />
To understand this, think of a circuit with two resistors of equal value in series, connected to a +5v source, becuase the resistances are equal, the voltage droop is equal, this kind of circuit is called a voltage divider, becuase the voltage in between the two resistors is 1/2 the input voltage. Again, imagine a circuit with 2 resistors in series connected to a +5v source, however this time, the resistors are 50 ohms and 25 ohms, becuase the total resistence (remember series resistance?) is 75 ohms, at 5v, we can calculate the current, and from there calculate the voltage drop from each resistor, you should have gotten 3.33 volts across the first, and 1.66 for the second one (I tried to pick better numbers, honest!); well, the voltage happens to be in the same ratio as the resistance values; now that we've proved that, we can apply it to the wheatstone bridge.<br /><br /><br />
With that in mind, we now know that the ratio of the resistors is what controls the voltage at the midpoint, so if two sets of resistors have the same ratio, then they would have the same voltage, see where I'm going? When the voltage across the bridge is 0, the sets of resistors(R1/R2 and R3/Rx) have the same voltage, and thus the same ratio of resistance values! Since we know the ratio of the first leg(R1/R2, remember we set R2 to a known value to balance the bridge...) and we know R3, it's fairly simple to solve for Rx.<br /><br /><br />
Now here's the fun part... What if you don't want to have to change R2? Well then, you can, using the same principle, take the voltage across the bridge, and calculate Rx from that... I'll leave out the derivation (Hey, it'd make good practice!), but basically, by applying all the concepts discussed here (Kirchhoff's laws, Ohm's law, etc) you end up at the equation <br /> <math>V_G = ({R_x \over {R_3 + R_x}} - {R_2 \over {R_1 + R_2}})</math><br />
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==Kirchhoff's Laws==<br />
Kirchhoff has two well-known laws of circuits: '''Kirchhoff's Current Law''' (KCL) and '''Kirchhoff's Voltage Law''' (KVL). They are simplifications of Maxwell's Laws of Electromagnetism that are valid for most practical circuits.<br />
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===Kirchhoff's Current Law===<br />
A '''node''' is a junction in a circuit where two or more electrical components meet. '''Kirchhoff's Current Law''' states that sum of currents entering a node is equal to the sum of currents leaving the node. This is based on the assumption that charges cannot accumulate in a node of the circuit. Equivalently, if one designates the direction of the currents with a sign (eg all currents leaving the node are negative), the sum of currents at each node equals zero.<br />
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====Node Method====<br />
The '''Node Method''' is a powerful tool of circuit analysis that is based upon Kirchhoff's Current Law. Basically, one writes the equation for every node in the circuit based upon unknown variables. Then from the resultant system of equations, one can calculate all the unknown variables and solve the circuit. It is often unnecessary for simple circuits, but becomes quite convenient for large circuits.<br />
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'''Detailed method:'''<br><br />
1. Select a node to be your '''ground''' and assign it a voltage of zero. (N.B. The term "ground" in the context of circuit analysis does not necessarily mean that it is connected to the ground. Instead, it is a node designated at zero electrical potential from which all other voltages are measures.)<br><br />
2. Assign every other node in the circuit a variable voltage. You may in certain cases be able to calculate a voltage for a few nodes (e.g. if the negative terminal of the battery is connected to the ground, the node connected to the positive terminal will have a known, positive voltage).<br><br />
3. Write the KCL equation for every node in the equation. [Example soon].<br><br />
4. Solve the resulting system of equations for all the unknown variables.<br />
At this point, you know the voltage for every node in the circuit and should be able to easily calculate anything else.<br />
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===Kirchhoff's Voltage Law===<br />
'''Kirchhoff's Voltage Law''' (KVL) states that for any closed loop in a circuit, the sum of voltages will be zero. One must be very careful with sign convention for this to work. For example, in a simple series circuit of resistors and voltage sources, one must choose either the voltage sources or the resistors to have negative voltages. This is based on the assumption that there is no changing magnetic field.<br />
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====Mesh Method====<br />
The '''Mesh Method''' is another technique of circuit analysis based upon Kirchhoff's Voltage Law. Essentially, one designates a variable for a current circulating through every loop in the circuit, and then writes an equation for each of these in terms of KVL.<br />
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==Equivalent circuits==<br />
Just as networks of individual resistors can be simplified into a single equivalent resistor, so also can more complicated networks. Any network containing resistors, current sources, and voltage sources can be transformed into a Thevenin or Norton equivalent. This is especially useful when analyzing circuits containing other components, as the entire rest of the circuit around the component may be a network which has an equivalent.<br />
===Thevenin equivalent===<br />
The Thevenin equivalent circuit between two points consists of a voltage source in series with a resistor. In order to find the Thevenin voltage, you must find the open-circuit voltage across the two points (ie when it is broken open). The resistance is found by removing all the power sources (replacing current sources with shorts and voltage sources with breaks) and finding the equivalent resistance of the resultant resistor network.<br />
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===Norton equivalent===<br />
The network can also be represented by a Norton equivalent. It consists of a resistor in parallel with a current source. The Norton resistance is equal to the Thevenin resistance. The Norton equivalent current is equal to the current that passes between the two points if you short circuit them.<br />
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==Other Topics==<br />
===Capacitors===<br />
Capacitors are, in DC at least, a device that stores a charge. When capacitors are in a circuit, they are said to resist change in voltage(i.e. if the voltage in a circuit goes up, the capacitor charges, taking away the excess voltage. If the voltage drops, the capacitor discharges, adding back to the circuit to make up the difference. There are many types of capacitors(Mylar, polystyrene, electrolytic, etc), but they all do the same basic job. At the most basic level, a capacitor is comprised of two plates separated by a dielectric(insulting material) that stores a charge, there's a few basic concepts it may be helpful to know. First off, look at the charging circuit below, the capacitor is uncharged in the beginning, but when the switch is closed, it begins to charge, as it starts to charge, the resistance across it is small(thus a current flows through the circuit, charging the capacitor), however as the voltage of the capacitor reaches <math>V_0</math>, the current decays exponentially, because the voltage is smaller, less current flows(remember?). This can also be shown by trying to measure the resistance of a capacitor(see below, because the meter puts out a small current, that charges the capacitor). Its useful to in some cases calculate the voltage for a capacitor as it is charging or discharging, for which 2 formulas are incredibly helpful. For a charging capacitor in an RC circuit Vc = Vo(1-e^(-t/(RC))) and for a discharging one, Vc = Vo(e^(-t/(RC))).<br />[[file:CapCharging.png|thumb|300px|center|Charging circuit, from wikipedia]]<br />
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'''Other Analogy'''<br /><br />
In the water analogy, a capacitor is simulated as a piece of rubber blocking the pipe. Using this example, we can see that a DC current would flow for a time, but when the rubber reached it's elastic limit, it would stop, the same as the capacitor charge curve discussed above. However, an AC current(imagine the water moving back and forth very fast) would simply move the rubber back and forth, never stopping the rubber on the other side from flowing(this is true for electricity, but in an effort to not drone on to long, it's not in there).<br />
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===Inductors===<br />
An inductor is basically an electromagnet, however it exhibits special characteristics in a circuit. In the most simple terms, it's the opposite of a capacitor, however this is slightly misleading. An inductor has an ability to store a charge in a magnetic field(whereas a capacitor stores it in an electric field) and has the ability to maintain a constant current in a circuit(whereas a capacitor can maintain a constant voltage). This means that an inductor can easily conduct DC(whereas a capacitor can easily conduct AC), however if AC is put through an inductor, the magnetic field will grow and collapse with the rise and fall of current, which tends to oppose the flow of AC through an inductor.<br />
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'''Other Analogy'''<br />
In the water analogy, an inductor is a waterwheel, with a constant flow of water through it, the waterwheel spins, and all is fine, however with an alternating flow, the water wheel is continuously trying to turn back and forth, limiting the flow of water.<br />
===Diodes===<br />
Don't let anything in here scare you, you probably only really need to know that a diode conducts only in one way, but hey, it never hurts to know more, right?<br />
This is a topic that's not covered very deeply in the rules, so I will only go over the basics in here. A diode is a semiconductor made of a junction of P-type and N-type silicon(don't worry to much about the details), it's special in that it only conducts in one direction. There are a lot of different types of diodes(schottky, zener, light emmitting diodes) they all vary in a few charecteristics, mainly, their forward voltage drop(how much voltage is lost while conducting), and avalanche voltage(point at which they coduct in reverse), for example, schottky diodes are used in power supplies when you need to combine two power supplies of the same voltage(so one doesn't backfeed the other) because of their charecteristcally low forward voltage drop, whereas zener diodes are used in applications where one needs to detect when a voltage is above a certain point becuase of their low avalanche voltage(put on in backwards and you'll only get a voltage on the other side of it when it crosses a certain point), light emmitting diodes are used... well... you should be able to figure that one out. The arrow on the symbol of a diode points the direction of the conventional (positive) current through the diode.<br /><br /><br />
'''Other Analogy'''<br />
In the water analogy, the diode is simply a check-valve(one way valve). That's it, nothing more to it.<br />
====Circuit Analysis with Ideal Diodes====<br />
Ideal diodes can generally be approximated by either a short or a break in the circuit. Generally to analyze a circuit with an ideal diode, one will make an educated guess on whether or not the diode will conduct. Once one finds a solution for this hypothesized circuit, one much check whether it makes sense. If you assumed the diode would conduct, you must make sure it is conducting current in the correct direction. If you assumed it does not conduct, you must check to make sure the voltage across the hypothetically non-conducting diode is such that it would not conduct. If this is not the case, you must switch your assumption and recalculate the circuit.<br />
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===Base and Derived Units===<br />
SI base units are the base quantities that are independent. There is a total of seven units, but the ones important to this event are meters (m, length), kilograms (kg, mass), amperes (A, electric current), and seconds (s, time). Derived units are units that come from a combination of the base units. The ones important to this event are newtons, joules, watts, coulombs, volts, farads, siemens, and ohms. The table below shows how each of the units is related. <br />
<br />
{|class="wikitable"<br />
|+Derived Units<br />
!Quantity measured<br />
!Unit name<br />
!Unit symbol<br />
!Expression in other SI Units<br />
!Base SI Units<br />
|-<br />
|Electrostatic Force<br />
|Newton<br />
|N<br />
| -<br />
|kg*m*s<sup>-2</sup><br />
|-<br />
|Energy, work<br />
|Joule<br />
|J<br />
|N*m<br />
|m<sup>2</sup>*kg*s<sup>-2</sup><br />
|-<br />
|Power<br />
|Watt<br />
|W<br />
|J/s<br />
|m<sup>2</sup>*kg*s<sup>-3</sup><br />
|-<br />
|Electric Charge<br />
|Coulomb<br />
|C<br />
| - <br />
|s*A<br />
|-<br />
|Electric Potential Difference<br />
|Volt<br />
|V<br />
|W/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-1</sup><br />
|-<br />
|Capacitance<br />
|Farad<br />
|F<br />
|C/V<br />
|s<sup>4</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|Electric Resistance<br />
|Ohm<br />
|Î©<br />
|V/A<br />
|m<sup>2</sup>*kg*s<sup>-3</sup>*A<sup>-2</sup><br />
|-<br />
|Electric Conductance<br />
|Sieman<br />
|S<br />
|A/V<br />
|s<sup>3</sup>*A<sup>2</sup>*m<sup>-2</sup>*kg<sup>-1</sup><br />
|-<br />
|}<br />
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Another important derived quantity that does not have a special unit name is the electric field strength, measured in V/m.<br><br />
One coulomb is also equal to the charge of 6.24 x 10<sup>18</sup> electrons.<br />
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===Meters===<br />
[[file:Meter.JPG|thumb|300px|center|This is a fairly complex Fluke 287 multimeter, note the separate jacks for measuring current.]]<br />
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During the event, the test may require you to measure certain values in a circuit, for this you can use either a multimeter or probes(whatever the ES gives you), but you have to know how to hook it up, or you could get yourself dq'd(I've seen this happen). Basically, there are three things that you could be asked to measure, voltage, current, or resistance. <br /><br /><br />
'''Voltage''' is fairly straightforward, you put the said device in voltage mode(make sure the probes are hooked up in the right place!) and put them across whatever you want to measure and it reads off a voltage(the difference in potential between the probes, the meter has a high enough resistance(called impedance) that it won't cause any significant amount of current to flow(most meters are around 11 million ohms!)). <br /><br /><br />
'''Current''' is another one you might be asked to measure, think of current as the flow-rate in the water analogy, to measure the flow, you have to 'get into' the circuit, this is why meters have a separate jack for current, there's a fuse in between the current jack and the common, and a low value(<5 ohms), by connecting the leads to the circuit, you allow current to flow with minimal resistance. The resistor in the circuit is called a shunt(that's just a big term for a resistor used to measure current) and by measuring the voltage across it, you can calculate the current(because the resistor has a constant value). Never put a meter set up to measure current in parallel with part of the circuit. You might blow a fuse in the meter or worse.<br /><br /><br />
'''Resistance''' is a little trickier, it can help to understand how the meter's going to measure it, basically, it puts out a small voltage(~2-3v) and measures the current that flows in the circuit, and calculates the resistance. This means that you can't measure resistance with power on the circuit, and you have to account for all the possible paths, not just the most direct route. Generally, one must first disconnect a component from the circuit before measuring the resistance. Never put an external voltage across a meter in resistance mode, as this could damage the meter.<br />
<br />
===AC Power===<br />
For more info, see [[AC Power|this page]].<br /><br/><br />
Up until now, the entire discussion(minus a mention when talking about capacitors) has dealt with DC, or direct current. In a DC circuit, current flows from the positive to the negative terminals of a battery or other source, that it(electrons flow the opposite, see above). However, the power in your house is AC, not DC(unless you live in a very strange house), AC, or alternating current, is a much more complicated beast. Basically, the direction of the current flow change, if you plotted voltage vs time, instead of a line, for DC, you would get a sine wave. This yields many advantages, namely, the use of transformers for voltage step-up/step-down. <br /><br /><br />
'''Transformers'''<br /><br />
Transformers are basically 2 electromagnets that are put together, most of the time sharing a common core of iron. Transformers work because the AC generates a constantly changing magnetic field in the primary coil, which can induce a charge in the secondary coil. It isn't possible to build a DC transformer because the magnetic field would be constant, remember that stable magnetic fields(stationary) can't induce a charge.(a changing field acts the same as a moving one). The ratio of the turns of the primary winding to the turns of the secondary is equal to the ratio of the primary voltage to the secondary(i.e. 2 turns on the primary and 1 on the secondary will half the primary voltage)<br />
<br />
===Digital Logic===<br />
<br />
In digital logic in circuits, a current corresponds to a "true" or "1", and no or very little current corresponds to a "false" or "0". A '''logic gate''' will take 1 or more of these signals, perform a logical operation on it, and then either send a true or a false on its way.<br />
<br />
A simple example of a logic gate is a transistor. If it receives very little current (false/0), then it does not allow current to pass through it (false/0). If it receives a current (true/1), then it allows current to pass through it (true/1).<br />
<br />
Here is a list of logic gates:<br />
*'''AND''' AND must have two trues in order for current to pass through it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!IN<br />
!PUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A AND B<br />
|-<br />
!0<br />
!0<br />
!0<br />
|-<br />
!0<br />
!1<br />
!0<br />
|-<br />
!1<br />
!0<br />
!0<br />
|-<br />
!1<br />
!1<br />
!1<br />
|-<br />
|}<br />
<br />
*'''OR''' OR will allow current to pass through it if any true is given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!IN<br />
!PUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A OR B<br />
|-<br />
!0<br />
!0<br />
!0<br />
|-<br />
!0<br />
!1<br />
!1<br />
|-<br />
!1<br />
!0<br />
!1<br />
|-<br />
!1<br />
!1<br />
!1<br />
|-<br />
|}<br />
<br />
*'''NOT''' NOT turns trues into falses and falses into trues. The NOT gate is commonly called an inverter.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!INPUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!NOT A<br />
|-<br />
!0<br />
!1<br />
|-<br />
!1<br />
!0<br />
|-<br />
|}<br />
<br />
*'''NAND''' NAND blocks current only when two trues are given to it.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!IN<br />
!PUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NAND B<br />
|-<br />
!0<br />
!0<br />
!1<br />
|-<br />
!0<br />
!1<br />
!1<br />
|-<br />
!1<br />
!0<br />
!1<br />
|-<br />
!1<br />
!1<br />
!0<br />
|-<br />
|}<br />
<br />
*'''NOR''' NOR only allows current to pass through it when it is given two falses.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!IN<br />
!PUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A NOR B<br />
|-<br />
!0<br />
!0<br />
!1<br />
|-<br />
!0<br />
!1<br />
!0<br />
|-<br />
!1<br />
!0<br />
!0<br />
|-<br />
!1<br />
!1<br />
!0<br />
|-<br />
|}<br />
<br />
*'''XOR''' XOR only allows current to pass through it when the two signals it is sent are not the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!IN<br />
!PUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XOR B<br />
|-<br />
!0<br />
!0<br />
!0<br />
|-<br />
!0<br />
!1<br />
!1<br />
|-<br />
!1<br />
!0<br />
!1<br />
|-<br />
!1<br />
!1<br />
!0<br />
|-<br />
|}<br />
<br />
*'''XNOR''' XNOR only allows current to pass through it when the two signals it is sent are the same.<br />
Truth Table:<br />
{|class = "wikitable"<br />
|-<br />
!IN<br />
!PUT<br />
!OUTPUT<br />
|-<br />
!A<br />
!B<br />
!A XNOR B<br />
|-<br />
!0<br />
!0<br />
!1<br />
|-<br />
!0<br />
!1<br />
!0<br />
|-<br />
!1<br />
!0<br />
!0<br />
|-<br />
!1<br />
!1<br />
!1<br />
|-<br />
|}<br />
<br />
[http://en.wikipedia.org/wiki/Logic_gate Information Source]<br />
<br />
==Resources==<br />
<br />
The rest of the "episodes" on circuitry, as well as circuit worksheets, can be found [[Circuit Lab (Episodes)|here]].<br />
The rules for a trial event form on Ciruit Lab can be found [http://soinc.org/sites/default/files/uploaded_files/trial_events/CircuitLab.pdf here]<br />
<br />
[[Media:SCIENCE OLYMPIAD CIRCUTE LAB MARCH 7TH.pdf| Circuit Lab Notes]]<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Lab Event Pages]]<br />
[[Category:Electricity/Electronics]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30609
Chemistry Lab/Electrochemistry
2014-04-07T20:56:05Z
<p>Voltage: /* Electron Potential */</p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
There are two different analogies for understanding electron potential or '''voltage'''.<br />
<br />
One is water. Electron potential corresponds to the water pressure. The higher the pressure, the stronger the stream that flows. Electron potential does not correspond to the strength of the stream, since different sized pipes with the same water pressure will have different strength streams.<br />
<br />
The second analogy is height. Higher electron potential corresponds to higher height. From higher height you can drop, while doing work, to lower height.<br />
<br />
Something to note is that electron potential is not absolute, it is with respect to. Standing on a 10 ft. high cliff and dropping a ball is the same as standing on the edge of a 10 ft. deep pit and dropping a ball (ignoring changes in gravity: analogies are not perfect). It is the same way with electron potential. You must define a zero before you can say what the electron potential is. Because of this it is quite possible to have negative electron potential.<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30585
Chemistry Lab/Electrochemistry
2014-04-06T13:05:32Z
<p>Voltage: /* Basic Information */</p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
When something is oxidized its oxidation number increases, and when something is reduced it's oxidation number decreases.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30584
Chemistry Lab/Electrochemistry
2014-04-06T13:04:15Z
<p>Voltage: /* Voltaic Cells */</p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
Another, more sure fire way of telling where oxidation and reduction occurs is as so: the cathode is positive (you can remember this by "cats are positive", even if they're not). Thus, electrons flow '''to''' the cathode, meaning that reduction is occurring at the cathode. This means that oxidation occurs at the anode.<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Ornithology&diff=30561
Ornithology
2014-04-05T22:47:46Z
<p>Voltage: </p>
<hr />
<div>{{EventLinksBox<br />
|2010tests=[http://scioly.org/wiki/2010_Test_Exchange#Ornithology 2010]<br />
|2010thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=67&t=1272 2010]<br />
|2011thread=[http://scioly.org/phpBB3/viewtopic.php?f=93&t=2209 2011]<br />
|2011tests=[http://scioly.org/wiki/2011_Test_Exchange#Ornithology 2011]<br />
|type=Life Science<br />
|cat=Study<br />
}}<br />
'''Ornithology''' is a science that concerns the study of birds. The competition includes both identification of birds and questions about bird characteristics (anatomy, diet, range, etc). There are 185 species on the Official Bird List for 2011, which are separated into 19 orders. Any of the species on the Official Bird List may be tested on during the competition. However, some states may use a modified bird list.<br />
<br />
Ornithology rotates with [[forestry]], [[entomology]], and [[herpetology]] every 2 years for both B and C division. The last time it was an event was [[2011]]. It was rotated out forestry [[2012]]-[[2013]] and forestry was rotated out for entomology in [[2014]].<br />
<br />
==Overview of the Event==<br />
This event is geared towards the study of birds. For the event, you need to know how to identify birds. In addition, there will be questions relating to any of the birds on the [http://soinc.org/sites/default/files/uploaded_files/Ornithology2010%20Bird%20List%207-16-09rev9-22.pdf Official Bird List]. You may need to know the call of any of the birds marked with a musical note.<br />
<br />
The event should be run either with stations, or as a powerpoint. Stations (or powerpoint slides) can include:<br />
<br />
* Live/preserved specimens<br />
* Skeletal material<br />
* [[Ornithology#Bird Calls|Recordings of songs]]<br />
* Slides or pictures of specimens<br />
<br />
Each team may bring one published [[Field Guides|field guide]] (two for nationals) which may be tabbed, written in, or drawn in, one double sided sheet of paper with notes in any form, and the two page Official Bird List.<br />
<br />
Identification questions can be to any level indicated on the Official Bird List.<br />
<br />
Questions about the birds may be about any of the following topics:<br />
<br />
* Life History<br />
* Distribution<br />
* [[Ornithology#Bird Anatomy|Anatomy]]<br />
* [[Ornithology#Physiology|Physiology]]<br />
* Reproduction<br />
* Habitat characteristics<br />
* Ecology<br />
** Behavior<br />
** Habitat<br />
** Symbiotic relationships<br />
** Trophic level<br />
** Adaptive anatomy<br />
*** Bill size and shape<br />
*** Migration<br />
*** Distribution<br />
*** Occurrence (common, rare, endangered, etc.)<br />
* Diet<br />
* Behavior<br />
* Conservation<br />
* Biogeography<br />
<br />
==Field Guides==<br />
===Peterson Field Guide to Birds of North America===<br />
* It includes all species that are on the national birds list.<br />
* It provides full color painted pictures of all birds which can be more useful than pictures for assistance in identification due to the more archetypal quality of the presentation.<br />
* It provides several painted representations of many species, usually of the different color patterns or body types seen in males, females, juveniles, and different plumages throughout the year.<br />
* Information on each species is relatively sparse to non-existant.<br />
* Very complete range maps are in the back.<br />
* This field guide is sold in the Science Olympiad store.<br />
<br />
===The Sibley Guide to Birds===<br />
* It includes all species that are on the national birds list.<br />
* It provides full color painted pictures of all birds which can be more useful than pictures for assistance in identification due to the more archetypal quality of the presentation.<br />
* It provides several painted representations of many species, usually of the different color patterns or body types seen in males, females, juveniles, and different plumages throughout the year.<br />
* Includes paintings of the birds in flight.<br />
* Information on each species is relatively sparse.<br />
* Large margins are suitable for notation.<br />
* Most editions are less cumbersome than the Sibley.<br />
<br />
===Smithsonian Field Guide to the Birds of North America===<br />
<br />
* It includes most species on the national birds list.<br />
* Every bird has one or more color photographs on it's own respective page.<br />
* Information in the book is much more complete than either the Sibley or Peterson.<br />
* Relatively little blank space is available for notation.<br />
* Less cumbersome than the Sibley or larger editions of the Peterson.<br />
<br />
===National Geographic Field Guide to the Birds of North America===<br />
<br />
* It includes most if not all species on the national birds list.<br />
* It provides several painted representations of many species, usually of the different color patterns or body types seen in males, females, juveniles, and different plumages throughout the year.<br />
* Information in the book is more complete than either the Sibley or Peterson.<br />
* There is more space in the margins than in the Smithsonian, but less than in the Sibley or Peterson.<br />
* Less cumbersome than the Sibley or larger editions of the Peterson.<br />
* It features a "Quick-Find Index".<br />
<br />
===Kaufman Field Guide to Birds of North America===<br />
<br />
* It includes most species on the national birds list.<br />
* Every bird has one or more color photographs on it's respective page.<br />
* Information in the book is much more complete than either the Sibley or Peterson.<br />
* Relatively little blank space is available for notation.<br />
* It has fewer pages than other mentioned books.<br />
* The guide is organized by bird family groupings rather than strict taxonomic classification; this is a feature that will appeal especially to beginners.<br />
* Color-coded tabs identify each grouping of birds (waders, warblers, sparrows, etc.) for quick thumb indexing.<br />
* Less cumbersome than the Sibley or larger editions of the Peterson.<br />
<br />
===Some Other Guides===<br />
* The guides above (with the exception of the Kaufman) come in eastern and western editions as well as the more complete editions mentioned above. These may be useful when paired together at the national tournament.<br />
* The Audubon produces turtleback field guides for eastern and western birds with picture plates and a medium amount of information on each bird.<br />
* There are several easy to use but light on information and identification "pocket-guides" such as the Golden guide series.<br />
* National Wildlife Federation Field Guide to Birds of North America<br />
* Birds of North America, Revised and Updated: A Guide To Field Identification, is the Golden guides more complete field guide.<br />
* American Museum of Natural History: Birds of North America (otherwise known as Vuilleumier) contains all but one bird (Northern Jacana) on the list and provides extensive information on each one, such as feeding and nesting, and also includes some trivia. It's more of an encyclopedia than a field guide.<br />
* DK Smithsonian Birds of North America is similar to the Vuilleumier, but provides even more information. However, its pictures are not very high quality.<br />
<br />
===Tips on choosing a field guide===<br />
* Different people have different needs, and a field guide that one person likes a lot may not work out for a different person.<br />
* When choosing your field guide, you must find a balance between ''identification'' and ''information''. <br />
* A guide that is good for identification may have many detailed drawings of each bird, such as the Sibley guide.<br />
* A guide that is good for information may have a paragraph or two relating to habitat, reproduction, etc. but only one or two photographs or drawings of the bird, such as the National Geographic guide.<br />
* In addition, the layout and size of the field guide must be taken into account. Guides that do not have most of the birds on the National List can be a big hindrance.<br />
* It is a good idea to obtain two contrasting guides and compare them to see which one is easier to use.<br />
* Remember, you can tab your field guide (to facilitate navigation) and write in it (to add information). If you plan on writing in your guide, you should get a guide with lots of extra space on the pages.<br />
<br />
===Other books===<br />
Here is a list of other books that can aid you in studying. Each book has a link to its Amazon page.<br />
<br />
[http://www.amazon.com/Sibley-Guide-Bird-Life-Behavior/dp/1400043867/ref=pd_sim_b_7 The Sibley Guide to Bird Life & Behavior] As the companion guide to The Sibley Guide to Birds, this book is very helpful and easy to study from. The book is split into two sections: the first provides information about general ornithology, while the second includes more specific info about each family of bird. Both sections are very easy to read and understand. Strongly recommended. <br />
<br />
[http://www.amazon.com/Ornithology-Frank-B-Gill/dp/0716724154 Ornithology - Frank B. Gill]<br />
This is a college level textbook that contains lots of information about many topics in ornithology. It gets to be very in-depth and contains much more information than what you actually need in the competition, but it is a great resource for accurate information.<br />
<br />
==Introduction to Ornithology==<br />
===What is a bird?===<br />
Any creature in the class Aves is a bird. More specifically, birds are distinguished from other organisms by feathers which cover their body, bills, and often complex songs and calls. Birds are warm blooded and are bipedal with forearms adapted to be wings, though in some species the wings have become vestigial and can no longer be used for flight.<br />
<br />
Birds have one of the most efficient respiratory systems among vertebrates, and they lay eggs that are unique for their hard shell.<br />
<br />
There are around 10,000 known species of birds, which are found all over the earth, and on every continent. Birds occupy a large range of habitats, making them the most numerous tetrapod vertebrates.<br />
<br />
===Bird Anatomy===<br />
====Topography====<br />
Topography refers to the external anatomy of a bird.<br />
The diagrams below show the basic parts of a bird.<br />
<br />
[[Image:birdtopography.jpg|thumb|300px|center|This diagram shows the major features of a bird's body.]]<br />
[[Image:birdhead.jpg|thumb|300px|center|This diagram shows the major features of a bird's head.]]<br />
<br />
====Physiology====<br />
<br />
=====Respiration=====<br />
A bird's respiratory system is one of the most efficient found in vertebrates. This is mainly because of their ability to fly, which creates a need for more oxygen.<br />
<br />
Air sacks are structures unique to birds, which take up 20% of a bird's internal body space. Air sacks store air, keeping a fixed volume in the lungs. There are two types of air sacks: anterior and posterior. Sometimes, air sacks rest inside the semi-hollow bones of birds. In addition, a bird's lungs take up half of the space that mammal's lungs do, yet weight does not decrease.<br />
<br />
When a bird takes a breath, air passes through the trachea either into the bird's lungs and then the anterior air sacks or directly into the posterior air sacks. Air in the anterior air sacks go directly through the trachea and back out of the nostrils, while air in the posterior air sacks go through the lungs, and then through the trachea as the bird exhales.<br />
<br />
One important adaption birds have made is that new oxygen and old, waste gasses are never mixed during respiration. Also, old air is almost completely replaced by new air when a bird takes a breath.<br />
<br />
=====Circulation=====<br />
Like many mammals (including humans), birds have a four-chambered heart. However, a bird's heart can be almost twice the size of a mammal's, and much more efficient, for the same reason as the circulatory system. Powerful flyers and divers have the largest heart relative to their body size.<br />
<br />
=====Skeleton=====<br />
A bird's skeleton is, in many ways, well adapted for flight. The major bones of a bird's skeleton have a hollow interior with crisscrossing "struts" to provide support. Some bones contain air sacks which are used by the respiratory system. Bird skeletons generally follow a specific format, with the exception of extreme specialization.<br />
<br />
[[File:Birdwing.gif]]<br><br />
[[File:Bird skeleton.jpg|right|300px]]<br />
The image above shows the bones in the average bird's wing, with the left side being the tip of the wing and the right side being where it connects to the bird's body. Notice how similar it is to a human arm. There are two major sections to the arm. The upper arm is made up of the humerus, while the lower arm consists of the radius and the ulna. Birds have 2 wrist bones (carpals). However, instead of having 5 metacarpals (hand bones), they have one bone called the carpometacarpus. This limits the mobility of the manus, but it is better adapted for flight. Birds have 3 digits and 4 finger bones (phalanges, singular phalanx). The middle and largest digit has to phalanges.<br />
<br />
Birds' legs are slightly more complicated. What most people think of as the knees of a bird are actually the ankles, as the knees (and the upper legs (femur)) are mostly hidden by feathers. Birds have a fuse and extended foot bone (tarsometatarsus) which most people think of as the lower leg, and which give birds three sections to the leg instead of 2. The bone in the actual lower leg is the tibiotarsus, a fusion of part of the tarsus with the tibia. Birds have (at most) four toes, although some birds have less (e.g. the ostrich, which only has two toes. Refer to the image at the right for leg anatomy, and the image below for toe variations.<br />
<br />
{|<br />
|[[File:Toearrangements.gif|thumb|450px|left|a = anisodactyl, b = zygodactyl, c = heterodactyl, d = syndactyl, & e = pamprodactyl]]<br />
|}<br />
<br />
* Anisodactyl feet have three toes forward and one backward. It's the most common toe configuration, and is used by songbirds and perching birds.<br />
<br />
* Zygodactyl feet have two toes forward and two toes backward. It's used by climbers such as woodpeckers because it enables a stronger grip on branches.<br />
<br />
* Heterodactyl feet are similar to zygodactyl ones except the second toe is reversed. It's only found on trogons.<br />
<br />
* Syndactyl feet have the third and fourth toe partially fused together. It's characteristic of Kingfishers.<br />
<br />
* Pamprodactyl feet have all four toes facing front. Swifts may use this configuration to get a better grip when hanging on the sides of chimneys or caves.<br />
<br />
===Feathers and Plumage===<br />
====Feathers====<br />
Birds are the only modern animals that have feathers. Feathers are made of beta-keratin, which also makes up the scales on bird's legs.<br />
<br />
[[Image:contourfeather.jpg|thumb|200px|right|The major parts of a typical contour feather.]]<br />
Contour feather - Any of the outermost feathers of a bird, forming the visible body contour and plumage. A contour feather consists of a middle shaft and a vane on both sides of the shaft. The calamus, or quill, is the base of the shaft, while the rachis supports the vanes.<br />
<br />
The vane of a contour feather is mainly made up of barbs, which consist of rami (s. ramus) sticking out vertically from the rachis. Each ramus contains barbules, which in turn have interlocking barbicels. This gives the vane of a contour feather a tight, smooth surface.<br />
[[Image:featherlocking.png|thumb|400px|center|The barbs on a typical contour feather.]]<br />
<br />
Flight feathers - These feathers are only found on the wings and the tail. They are large, stiff, and aerodynamic, which is helpful in flight. There are three main types of flight feathers: primaries, secondaries, and tertiaries. In addition, feathers called coverts cover the bases of the flight feathers.<br />
<br />
Down feather - A feather that has plumulaceous barbs. It is mostly used for insulation. Down feathers do not have a rachis; barbs are attached directly to the quill.<br />
<br />
Semiplumes - Feathers with a long rachis and plumulaceous barbs. Like down feathers, semiplumes mainly provide insulation.<br />
<br />
Filoplumes - Small feathers with a long rachis, but only a few barbs at the top. Filoplumes are attached to nerve endings at the base, letting them send information to the brain about the placement of contour feathers.<br />
<br />
Bristles - Stiff feathers with some barbs found at the base. Bristles are almost always found on the face of birds. Bristles have many possible applications, including protection from insects and dust, and acting as a "net" to aid in catching insects.<br />
<br />
==Species of Birds==<br />
This section contains information about individual orders, families and species. The birds are in the same order as they are on the Official Bird List. Images of each bird, as well as comments on their identification, can be found at the page [[2011 Bird List]].<br />
<br />
*[[Ornithology/Anseriformes|Anseriformes]]<br />
*[[Ornithology/Galliformes|Galliformes]]<br />
*[[Ornithology/Gaviiformes|Gaviiformes]]<br />
*[[Ornithology/Podicipediformes|Podicipediformes]]<br />
*[[Ornithology/Procellariiformes|Procellariiformes]]<br />
*[[Ornithology/Pelecaniformes|Pelecaniformes]]<br />
*[[Ornithology/Ciconiiformes|Ciconiiformes]]<br />
*[[Ornithology/Falconiformes|Falconiformes]]<br />
*[[Ornithology/Gruiformes|Gruiformes]]<br />
*[[Ornithology/Charadriiformes|Charadriiformes]]<br />
*[[Ornithology/Columbiformes|Columbiformes]]<br />
*[[Ornithology/Cuculiformes|Cuculiformes]]<br />
*[[Ornithology/Strigiformes|Strigiformes]]<br />
*[[Ornithology/Caprimulgiformes|Caprimulgiformes]]<br />
*[[Ornithology/Apodiformes|Apodiformes]]<br />
*[[Ornithology/Trogoniformes|Trogoniformes]]<br />
*[[Ornithology/Coraciiformes|Coraciiformes]]<br />
*[[Ornithology/Piciformes|Piciformes]]<br />
*[[Ornithology/Passeriformes|Passeriformes]]<br />
<br />
==Bird Calls==<br />
{|class="sortable" style="text-align:center"<br />
|+Note: This chart includes all of the calls of the birds that are indicated for vocal identification on the National Bird List.<br />
!Order!!Family!!Species!!Common Name!!Link<br />
|-<br />
|Anseriformes||Anatidae||Cygnus buccinators||Trumpeter Swan||[http://www.mnbirdtrail.com/sounds/trumpet.wav Call]<br />
|-<br />
|Anseriformes||Anatidae||Anas platyrhynchos||Mallard||[http://macaulaylibrary.org/audio/137827 Call]<br />
|-<br />
|Galliformes||Phasianidae||Bonasa umbellus||Ruffed Grouse||[http://www.uwgb.edu/birds/wbba/species/audios/GROUSE__RUFFED.MP3 Call]<br />
|-<br />
|Galliformes||Phasianidae||Tympanuchus cupido||Greater Prairie-Chicken||[http://macaulaylibrary.org/audio/50136 Call]<br />
|-<br />
|Galliformes||Odontophoridae||Colinus virginianus||Northern Bobwhite||[http://macaulaylibrary.org/audio/105364 Call]<br />
|-<br />
|Gaviiformes||Gaviidae||Gavia stellata||Red-throated Loon||[http://macaulaylibrary.org/audio/132108 Call]<br />
|-<br />
|Ciconiiformes||Ardeidae||Botaurus lentiginosus||American Bittern||[http://macaulaylibrary.org/audio/53166 Call]<br />
|-<br />
|Falconiformes||Accipitridae||Haliaeetus leucocephalus||Bald Eagle||[http://www.allaboutbirds.org/guide/Bald_Eagle/sounds Call]<br />
|-<br />
|Falconiformes||Accipitridae||Buteo jamaicensis||Red-tailed Hawk||[http://fsc.fernbank.edu/Birding/bird_sounds/rtha.mp3 Call]<br />
|-<br />
|Gruiformes||Rallidae||Porzana carolina||Sora||[http://www.uwgb.edu/birds/wbba/species/audios/RAIL__SORA.MP3 Call]<br />
|-<br />
|Gruiformes||Gruidae||Grus americana||Whooping Crane||[http://macaulaylibrary.org/audio/2747 Call]<br />
|-<br />
|Charadriiformes||Charadriidae||Charadrius vociferus||Killdeer||[http://www.mbr-pwrc.usgs.gov/id/framlst/Song/h2730so.mp3 Call]<br />
|-<br />
|Charadriiformes||Scolopacidae||Bartramia longicauda||Upland Sandpiper||[http://www.uwgb.edu/birds/wbba/species/audios/SANDPIPER__UPLAND.MP3 Call]<br />
|-<br />
|Columbiformes||Columbidae||Zenaida asiatica||White-winged Dove||[http://macaulaylibrary.org/audio/45162 Call]<br />
|-<br />
|Columbiformes ||Columbidae ||Zenaida macroura||Mourning Dove||[http://www.uwgb.edu/birds/wbba/species/audios/DOVE__MOURNING.MP3 Call]<br />
|-<br />
|Cuculiformes||Cuculidae||Coccyzus erythropthalmus||Black-billed Cuckoo||[http://www.uwgb.edu/birds/wbba/species/audios/CUCKOO__BLACK_BILLED.MP3 Call]<br />
|-<br />
|Cuculiformes||Cuculidae||Geococcyx californianus||Greater Roadrunner||[http://macaulaylibrary.org/audio/8287 Call]<br />
|-<br />
|Strigiformes||Strigidae||Bubo virginianus||Great Horned Owl||[http://macaulaylibrary.org/audio/22873 Call]<br />
|-<br />
|Strigiformes||Strigidae||Strix varia||Barred Owl||[http://macaulaylibrary.org/audio/125371 Call]<br />
|-<br />
|Caprimulgiformes||Caprimulgidae||Nyctidromus albicollis||Common Pauraque||[http://identify.whatbird.com/obj/858/overview/Common_Pauraque.aspx Call]<br />
|-<br />
|Caprimulgiformes||Caprimulgidae||Caprimulgus carolinensis||Chuck-willâ€™s-widow ||[http://macaulaylibrary.org/audio/105213 Call]<br />
|-<br />
|Caprimulgiformes||Caprimulgidae||Caprimulgus vociferus||Whip-poor-will||[http://www.mbr-pwrc.usgs.gov/id/framlst/Song/h4170so.mp3 Call]<br />
|-<br />
|Coraciiformes||Alcedinidae||Megaceryle alcyon||Belted Kingfisher||[http://macaulaylibrary.org/audio/6562 Call] <br />
|-<br />
|Passeriformes||Tyrannidae||Contopus cooperi||Olive-sided Flycatcher|| [http://macaulaylibrary.org/audio/44937 Call] <br />
|-<br />
|Passeriformes||Tyrannidae||Myiarchus crinitus||Great Crested Flycatcher||[http://macaulaylibrary.org/audio/94314 Call]<br />
|-<br />
|Passeriformes||Tyrannidae||Tyrannus verticalis||Western Kingbird||[http://macaulaylibrary.org/audio/56905 Call]<br />
|-<br />
|Passeriformes||Vireonidae||Vireo gilvus||Warbling Vireo||[http://www.uwgb.edu/birds/wbba/species/audios/VIREO__WARBLING.MP3 Call]<br />
|-<br />
|Passeriformes||Vireonidae||Vireo olivaceus||Red-eyed Vireo||[http://www.allaboutbirds.org/guide/Red-eyed_Vireo/sounds Call]<br />
|-<br />
|Passeriformes||Corvidae||Cyanocitta cristata||Blue Jay||[http://macaulaylibrary.org/audio/49716 Call]<br />
|-<br />
|Passeriformes||Corvidae||Corvus brachyrhynchos||American Crow||[http://macaulaylibrary.org/audio/135436 Call]<br />
|-<br />
|Passeriformes||Corvidae||Corvus corax||Common Raven||[http://macaulaylibrary.org/audio/132161 Call]<br />
|-<br />
|Passeriformes||Paridae||Poecile carolinensis||Carolina Chickadee||[http://macaulaylibrary.org/audio/84821 Call]<br />
|-<br />
|Passeriformes||Paridae||Baeolophus bicolor||Tufted Titmouse||[http://macaulaylibrary.org/audio/94271 Call]<br />
|-<br />
|Passeriformes||Sittidae||Sitta canadensis||Red-breasted Nuthatch||[http://macaulaylibrary.org/audio/50328 Call]<br />
|-<br />
|Passeriformes||Troglodytidae||Catherpes mexicanus||Canyon Wren||[http://macaulaylibrary.org/audio/40607 Call]<br />
|-<br />
|Passeriformes||Turdidae||Hylocichla mustelina||Wood Thrush||[http://macaulaylibrary.org/audio/11316 Call]<br />
|-<br />
|Passeriformes||Turdidae||Turdus migratorius||American Robin||[http://macaulaylibrary.org/audio/94261 Call]<br />
|-<br />
|Passeriformes||Mimidae||Mimus polyglottos||Northern Mockingbird|| [http://macaulaylibrary.org/audio/94373 Call]<br />
|-<br />
|Passeriformes||Mimidae||Toxostoma rufum||Brown Thrasher||[http://macaulaylibrary.org/audio/94278 Call] <br />
|-<br />
|Passeriformes||Parulidae||Oporornis formosus||Kentucky Warbler||[http://macaulaylibrary.org/audio/94330 Call]<br />
|-<br />
|Passeriformes||Parulidae||Icteria virens||Yellow-breasted Chat||[http://www.allaboutbirds.org/guide/Yellow-breasted_Chat/sounds Call]<br />
|-<br />
|Passeriformes||Emberizidae||Pipilo maculatus||Spotted Towhee||[http://www.allaboutbirds.org/guide/Spotted_Towhee/sounds Call]<br />
|-<br />
|Passeriformes||Emberizidae||Zonotrichia querula||Harrisâ€™s Sparrow||[http://www.allaboutbirds.org/guide/Harriss_Sparrow/sounds Call]<br />
|-<br />
|Passeriformes||Cardinalidae||Cardinalis cardinalis||Northern Cardinal||[http://www.allaboutbirds.org/guide/Northern_Cardinal/sounds Call]<br />
|-<br />
|Passeriformes||Cardinalidae||Passerina cyanea||Indigo Bunting||[http://www.allaboutbirds.org/guide/Indigo_Bunting/sounds Call]<br />
|-<br />
|Passeriformes||Icteridae||Agelaius phoeniceus||Red-winged Blackbird||[http://www.allaboutbirds.org/guide/Red-winged_Blackbird/sounds Call]<br />
|-<br />
|Passeriformes||Icteridae||Sturnella neglecta||Western Meadowlark||[http://www.allaboutbirds.org/guide/Western_Meadowlark/sounds Call]<br />
|-<br />
|Passeriformes||Icteridae||Icterus galbula||Baltimore Oriole||[http://www.allaboutbirds.org/guide/Baltimore_Oriole/sounds Call] <br />
|}<br />
<br />
==FAQ==<br />
This section addresses questions which are commonly brought up by those who are new to the event.<br />
<br />
;Q - What field guide should I use? <br />
A - This depends on your personal preferences, as well as your strong and weak points. However, three of the main field guides seem to be the Sibley, Peterson, and NatGeo. The one recommended in the rules is Peterson's. It has very good illustrations and information on every bird on the national list. <br />
However, the Sibley guide has very good illustrations of the juvenile, male, and female birds. (So it is good for IDing birds) <br />
<br />
;Q - Are we allowed to bring two books and note sheets, or just one?<br />
A:You are allowed to bring one book and sheet of notes per person. That means a maximum of two per team.<br />
<br />
;Q - Are we only allowed to use field guides, or can we use other books instead?<br />
A - The rules say you may use any published books, so they do not have to be field guides. You might want to bring a few guides as backup just in case the event supervisors interpret that rule differently.<br />
<br />
;Q - Should I use Wikipedia as a resource?<br />
A - Wikipedia often has good, accessible information, but since it can be easily modified you should always cross reference with a more reliable source.<br />
<br />
==Glossary==<br />
{|class="sortable" style="text-align:center"<br />
|+A glossary of terms related to ornithology.<br />
!Word!!Definition<br />
|-<br />
|Altricial||When a hatchling is completely dependent on its parents.<br />
|-<br />
|Bird Topography||The external anatomy of birds; anatomical features that can be observed on the outside of a bird's body.<br />
|-<br />
|Contour Feather||Any of the outermost feathers of a bird, forming the visible body contour and plumage.<br />
|-<br />
|Down||A layer of fine feathers found under the tougher exterior feathers.<br />
|-<br />
|External Anatomy||See ''Bird Topography''<br />
|-<br />
|Feather (n)||Any of the light horny epidermal outgrowths that form the external covering of the body of birds and that consist of a shaft bearing on each side a series of barbs which bear barbules which in turn bear barbicels commonly ending in hooked hamuli and interlocking with the barbules of an adjacent barb to link the barbs into a continuous vane.<br />
|-<br />
|Feather (v)||To grow feathers.<br />
|-<br />
|Feather Tract||See ''pterylae''<br />
|-<br />
|Horns||Paired contour feathers arising from head.<br />
|-<br />
|Lower Mandible||The lower part of the bill.<br />
|-<br />
|Plumulaceous||Downy; bearing down.<br />
|-<br />
|Precocial||Hatching fully developed, ready for activity, not completely dependent on parents.<br />
|-<br />
|Pterylae||Areas of the skin from which feathers grow. <br />
|-<br />
|Upper Mandible||The upper part of the bill.<br />
|}<br />
<br />
A more detailed glossary can be found at Cornells Birds[http://www.birds.cornell.edu/education/educators/glossary/] and Manitoba Museum of Man and Nature Bird and Binder Page [http://www.virtualmuseum.ca/Exhibitions/Birds/MMMN/English/glossary_data.html]<br />
<br />
==Sample Questions and Answers==<br />
What is the difference between precocial and altricial young?<br />
<spoiler text="Answer"> Precocial youung are born with open eyes and down. They are capable of leaving the nest within 2 days of hatching. Altricial young are born with closed eyes and no down. They rely on parents for survival. All passerines are altricial. </spoiler><br />
<br />
What is the purpose of lobed feet? <spoiler text="Answer"> They allow birds to walk across marshes by increasing surface area, but provides more toe maneuverability than webbing. Coots and Grebes have lobed feet. </spoiler><br />
<br />
Describe three abilities that are unique to hummingbirds. <spoiler text="Answer"> Hummingbirds drink nectar, can hover and fly backwards, and their tiny legs and feet make them incapable of walking. </spoiler><br />
<br />
==Links==<br />
[http://soinc.org/sites/default/files/uploaded_files/Ornithology2010OfficialList7-16-09.pdf 2010 National Bird List]<br />
<br />
[http://www.allaboutbirds.org/ The Cornell Lab of Ornithology]<br />
<br />
[http://www.mbr-pwrc.usgs.gov/id/framlst/infocenter.html/ Patuxent Bird Identification InfoCenter]<br />
<br />
[http://people.eku.edu/ritchisong/externalanatomy.html Bird external anatomy -- good examples of bill characteristics]<br />
<br />
[http://en.wikipedia.org/wiki/Bird The Wikipedia article on birds]<br />
<br />
[http://www.audubon.org/net/link/index.html Audubon links -- scroll down to the ornithology section]<br />
<br />
[http://www.birds.cornell.edu/AllAboutBirds/birding123/identify/allaboutbirds_quiz Good practice game for identifying -- click "Choose Specific Birds" to pick which ones can appear in the quiz.]<br />
<br />
[http://www.sciencenc.com/event-help/ornithology.php The North Carolina state SciOly sight -- Has links to all bird calls you must know]<br />
<br />
{{Living ID}}<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Study Event Pages]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Forestry&diff=30560
Forestry
2014-04-05T22:46:32Z
<p>Voltage: </p>
<hr />
<div>{{EventLinksBox<br />
|type=Life Science<br />
|cat=Study<br />
|2011thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=93&t=2842 2011 Preliminary]<br />
|2012thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=121&t=2967 2012]<br />
|2012tests=I like how this template is programmed so you can type anything in this space and it still links to the right place.<br />
|2013thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=144&t=3696 2013]<br />
|2013tests=Yes, it's very useful, saves a lot of tedious copying and pasting<br />
|B Champion=[[Solon Middle School]]<br />
|C Champion=[[Palo Alto High School]]<br />
}}<br />
<br />
Forestry is an identification event for both divisions. The event consists of identifying trees on the [[Media:ForestryTreeListFinal2013.pdf|Official Tree List]] and answering general questions about them. It is on a 2-year rotation with three other events: [[entomology]], [[herpetology]], and [[ornithology]]. The last time it was an event was in 2013.<br />
<br />
If you are interested in improving pages about forestry on the wiki, join [[Forestry/Wikifire|Operation Wikifire]]!<br />
<br />
==Event overview==<br />
<br />
Forestry is an event in which participants learn about a variety of North American trees. The competition is usually 3/4 identification and 1/4 knowledge-based questions about habitats, adaptions to the environment, biomes, succession, and relationships with animals or other plants. There may also be questions about trees and forestry in general. Guides to identification and studying will be included below.<br />
<br />
Most competitions will likely be run in stations, with a specimen or photograph to identify at each station and several questions about the tree. It is required under the 2012-2013 rules that a picture of a leaf be provided for each identification. Additionally, pictures of tree shape, flowers, seeds/fruits/cones, and variations may be given. Typically 1-3 minutes are given for each station. The event may also be run as a powerpoint or a written test.<br />
<br />
In the event of a station test, you will be provided an answer sheet. Make sure to write clearly, note the team name and number in the space provided, and erase any answers you changed. Remember to underline the genus and species of identified specimens on your answer sheet. Do not leave any blanks or incomplete questions.<br />
<br />
Teams may and should bring:<br />
<ul><br />
<li>Two 8.5" x 11" double-sided page of [[Notes]] (Tree List Included)</li><br />
<li>Two commercially published [[Field Guides|field guides]] (Can be tabbed, 3 words max per tab)</li><br />
</ul><br />
<br />
==Tree lists==<br />
<br />
*[[Media:ForestryTreeListFinal2013.pdf|2013 Official Tree List]]<br />
*[[Forestry/Tree List|Detailed Information and Descriptions About Each Tree]] <br />
<br />
The tree list may vary from state to state, so that local trees can be tested rather than trees from another region of the country. At the national level, all trees may be asked from the national tree list.<br />
<br />
===Old Lists===<br />
*[[Media:ForestrytreelistFINAL.pdf|2012 Official Tree List]]<br />
*[[Media:Forestry_tree_list.pdf|Nationals 2004]]<br />
*[[Media:Forestry05-MN-list.xls|Minnesota 2005]]<br />
*[[Media:Forestry RI 2005 list.pdf|Rhode Island 2005]]<br />
*[http://lionsden.tec.selu.edu/~scienceolympiad/treelist.html Louisiana 2005]<br />
<br />
==Resources==<br />
''For more detailed information about field guides and other resources, see the [[Forestry/Resources|Forestry Resources Page]].''<br />
<br />
A team may bring in two commercially published field guides to the test to aid them in identification and answering questions, in adition to two pages of notes. A combination of student developed notes and professional guides tend to have the best results. Participants should be familiar with their resources and be able to quickly find what they are looking for in order to take advantage of them. <br />
A good resource page in a field guide about a specific tree should contain: <br />
*Scientific name of specimen <br />
*Common name of specimen <br />
*Picture of specimen leaves, bark, wood, fruit, seeds, etc. <br />
*Page number in a specific guide <br />
*Habitat of specimen <br />
*Commercial uses of specimen <br />
*Pests or diseases that affect the specimen<br />
*Any other facts about the specimen deemed important by the team <br />
<br />
The most common professional guides to use are the National Audubon Society Field Guides (Eastern and Western editions) and field guides specific to an area (such as a state).<br />
<br />
Student notesheets should contain more general information. More general biology topics such as root systems, bark layers, photosynthesis, forest diversity, and any useful vocabulary are recommened to have on your notesheet. A tree list may be a part of the two allowed pages if the competitors feel as if they want that resource.<br />
<br />
==Introduction to Forestry==<br />
''For a more detailed introduction, see the [[Forestry/Introduction to Trees|Introduction to Trees]]<br />
<br />
===What is a tree?===<br />
Trees aren't a formally defined taxonomic group like birds or insects. Trees are just very large plants, and can be found in families and genera which also contain smaller plants and shrubs. There is a sort of continuum between shrubs and trees â€“Â even within a species, plants can range from a mere few feet tall to hundreds of feet tall. However, for the purposes of field guides, there are some general characteristics that most trees share which allow classification to be facilitated.<br />
<br />
*Trees are perennial.<br />
*Trees have a single woody stem which branches into a crown of foliage.<br />
*Trees reach a height of at least 10-20 feet.<br />
<br />
Don't think of this definition as the ultimatum for deciding what a tree is. There are many exceptions to the above, and many people have debated over the definition of a tree throughout history.<br />
<br />
== Tree Identification ==<br />
''For ID tips and information about specific trees, see the [[Forestry/Tree List|Forestry Tree List]].''<br />
<br />
There are several methods for quick identification of a specimen. There are two things to be considered before identifying: <br />
What sort of sample (leaf, bark, wood, fruit, or seed) do you have? <br />
What is the easiest way to identify using this sample? <br />
<br />
===If The Sample is a Leaf===<br />
<br />
If the sample is a leaf, the easiest catchall method of identification is [[Leaf Types|leaf shape]]. [[Leaf Types|Leaf shape]] can be broken down into a few, distinct families:<br />
<br />
====Conifer==== <br />
<br />
*Needle-Like <br />
*Scale-Like <br />
====Broadleaf==== <br />
<br />
*Compound Leaves <br />
**Pinnate <br />
**Palmate <br />
*Oak Shape <br />
*Maple Shape <br />
*Elm Shape <br />
*Other Shapes (Heart-shaped, circular, lance-shaped, triangular, obovate, ovate, etc.)<br />
<br />
===If the Sample is a Fruit===<br />
<br />
Fruits are unique to the species they come from. There may be similarities between fruits, but all are easily differentiated (for example, the Black Cherry, ''Prunus serotina'', has fruits similar to the Chokecherry, ''Prunus virginiana'', except that they are black when ripe). Most fruits come from trees with elm-shaped leaves. <br />
<br />
===If the Sample is Not a Leaf or Fruit===<br />
<br />
Many other samples are given alongside leaves, and few are given alone. If bark, wood, or seeds are given, there is probably something significant about that particular tree (for example, the Paper Birch, ''Betula papyrifera'', has unique bark and a buckeye is a seed unique to the Ohio Buckeye, ''Aesculus glabra'', so they may be given for identification)<br />
<br />
==Example of a Test Question==<br />
<br />
===Question=== <br />
[[File:MysteryLeaf.jpg]]<br />
<br />
Identify this specimen. <br />
#What is the common name of this specimen? <br />
#What time of year does this species flower? <br />
#What is the main commercial use of this tree?<br />
<br />
===Answer===<br />
<br />
<spoiler text="Answer(click to open)"><br />
''Cercis canadensis'' <br />
#(Eastern) Redbud <br />
#Spring <br />
#Ornamental<br />
</spoiler><br />
<br />
==See Also==<br />
*[[Forestry/Tabbing Tips|Tabbing Tips]]<br />
*[[Forestry/Resources|Forestry Resources]]<br />
*[[Forestry/Introduction to Trees|Introduction to Trees]]<br />
*[[Forestry/Tree List|Tree List]]<br />
*[[Forestry/Photosynthesis|Photosynthesis]]<br />
*[[Forestry/Leaf Types|Leaf Types]]<br />
*[[Forestry/Ginkgoaceae]]<br />
*[[Forestry/Pinaceae]]<br />
*[[Forestry/Taxaceae]]<br />
*[http://scioly.org/w/images/1/13/Forestry_coach_clinic_handout_text.pdf Science Olympiad Coaches Workshop; Hammond, IN]<br />
*[[Forestry/Wikifire]]<br />
<br />
{{Living ID}}<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Study Event Pages]]<br />
[[Category:Forestry]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Ornithology&diff=30559
Ornithology
2014-04-05T22:44:58Z
<p>Voltage: </p>
<hr />
<div>{{EventLinksBox<br />
|2010tests=[http://scioly.org/wiki/2010_Test_Exchange#Ornithology 2010]<br />
|2010thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=67&t=1272 2010]<br />
|2011thread=[http://scioly.org/phpBB3/viewtopic.php?f=93&t=2209 2011]<br />
|2011tests=[http://scioly.org/wiki/2011_Test_Exchange#Ornithology 2011]<br />
|type=Life Science<br />
|cat=Study<br />
}}<br />
'''Ornithology''' is a science that concerns the study of birds. The competition includes both identification of birds and questions about bird characteristics (anatomy, diet, range, etc). There are 185 species on the Official Bird List for 2011, which are separated into 19 orders. Any of the species on the Official Bird List may be tested on during the competition. However, some states may use a modified bird list.<br />
<br />
Ornithology rotates with [[forestry]], [[entomology]], and [[herpetology]] every 2 years for both B and C division. 2011 was the last time it was an event. It was rotated out forestry [[2012]]-[[2013]] and forestry was rotate out for entomology in [[2014]]. It is unknown when it will be rotated back in.<br />
<br />
==Overview of the Event==<br />
This event is geared towards the study of birds. For the event, you need to know how to identify birds. In addition, there will be questions relating to any of the birds on the [http://soinc.org/sites/default/files/uploaded_files/Ornithology2010%20Bird%20List%207-16-09rev9-22.pdf Official Bird List]. You may need to know the call of any of the birds marked with a musical note.<br />
<br />
The event should be run either with stations, or as a powerpoint. Stations (or powerpoint slides) can include:<br />
<br />
* Live/preserved specimens<br />
* Skeletal material<br />
* [[Ornithology#Bird Calls|Recordings of songs]]<br />
* Slides or pictures of specimens<br />
<br />
Each team may bring one published [[Field Guides|field guide]] (two for nationals) which may be tabbed, written in, or drawn in, one double sided sheet of paper with notes in any form, and the two page Official Bird List.<br />
<br />
Identification questions can be to any level indicated on the Official Bird List.<br />
<br />
Questions about the birds may be about any of the following topics:<br />
<br />
* Life History<br />
* Distribution<br />
* [[Ornithology#Bird Anatomy|Anatomy]]<br />
* [[Ornithology#Physiology|Physiology]]<br />
* Reproduction<br />
* Habitat characteristics<br />
* Ecology<br />
** Behavior<br />
** Habitat<br />
** Symbiotic relationships<br />
** Trophic level<br />
** Adaptive anatomy<br />
*** Bill size and shape<br />
*** Migration<br />
*** Distribution<br />
*** Occurrence (common, rare, endangered, etc.)<br />
* Diet<br />
* Behavior<br />
* Conservation<br />
* Biogeography<br />
<br />
==Field Guides==<br />
===Peterson Field Guide to Birds of North America===<br />
* It includes all species that are on the national birds list.<br />
* It provides full color painted pictures of all birds which can be more useful than pictures for assistance in identification due to the more archetypal quality of the presentation.<br />
* It provides several painted representations of many species, usually of the different color patterns or body types seen in males, females, juveniles, and different plumages throughout the year.<br />
* Information on each species is relatively sparse to non-existant.<br />
* Very complete range maps are in the back.<br />
* This field guide is sold in the Science Olympiad store.<br />
<br />
===The Sibley Guide to Birds===<br />
* It includes all species that are on the national birds list.<br />
* It provides full color painted pictures of all birds which can be more useful than pictures for assistance in identification due to the more archetypal quality of the presentation.<br />
* It provides several painted representations of many species, usually of the different color patterns or body types seen in males, females, juveniles, and different plumages throughout the year.<br />
* Includes paintings of the birds in flight.<br />
* Information on each species is relatively sparse.<br />
* Large margins are suitable for notation.<br />
* Most editions are less cumbersome than the Sibley.<br />
<br />
===Smithsonian Field Guide to the Birds of North America===<br />
<br />
* It includes most species on the national birds list.<br />
* Every bird has one or more color photographs on it's own respective page.<br />
* Information in the book is much more complete than either the Sibley or Peterson.<br />
* Relatively little blank space is available for notation.<br />
* Less cumbersome than the Sibley or larger editions of the Peterson.<br />
<br />
===National Geographic Field Guide to the Birds of North America===<br />
<br />
* It includes most if not all species on the national birds list.<br />
* It provides several painted representations of many species, usually of the different color patterns or body types seen in males, females, juveniles, and different plumages throughout the year.<br />
* Information in the book is more complete than either the Sibley or Peterson.<br />
* There is more space in the margins than in the Smithsonian, but less than in the Sibley or Peterson.<br />
* Less cumbersome than the Sibley or larger editions of the Peterson.<br />
* It features a "Quick-Find Index".<br />
<br />
===Kaufman Field Guide to Birds of North America===<br />
<br />
* It includes most species on the national birds list.<br />
* Every bird has one or more color photographs on it's respective page.<br />
* Information in the book is much more complete than either the Sibley or Peterson.<br />
* Relatively little blank space is available for notation.<br />
* It has fewer pages than other mentioned books.<br />
* The guide is organized by bird family groupings rather than strict taxonomic classification; this is a feature that will appeal especially to beginners.<br />
* Color-coded tabs identify each grouping of birds (waders, warblers, sparrows, etc.) for quick thumb indexing.<br />
* Less cumbersome than the Sibley or larger editions of the Peterson.<br />
<br />
===Some Other Guides===<br />
* The guides above (with the exception of the Kaufman) come in eastern and western editions as well as the more complete editions mentioned above. These may be useful when paired together at the national tournament.<br />
* The Audubon produces turtleback field guides for eastern and western birds with picture plates and a medium amount of information on each bird.<br />
* There are several easy to use but light on information and identification "pocket-guides" such as the Golden guide series.<br />
* National Wildlife Federation Field Guide to Birds of North America<br />
* Birds of North America, Revised and Updated: A Guide To Field Identification, is the Golden guides more complete field guide.<br />
* American Museum of Natural History: Birds of North America (otherwise known as Vuilleumier) contains all but one bird (Northern Jacana) on the list and provides extensive information on each one, such as feeding and nesting, and also includes some trivia. It's more of an encyclopedia than a field guide.<br />
* DK Smithsonian Birds of North America is similar to the Vuilleumier, but provides even more information. However, its pictures are not very high quality.<br />
<br />
===Tips on choosing a field guide===<br />
* Different people have different needs, and a field guide that one person likes a lot may not work out for a different person.<br />
* When choosing your field guide, you must find a balance between ''identification'' and ''information''. <br />
* A guide that is good for identification may have many detailed drawings of each bird, such as the Sibley guide.<br />
* A guide that is good for information may have a paragraph or two relating to habitat, reproduction, etc. but only one or two photographs or drawings of the bird, such as the National Geographic guide.<br />
* In addition, the layout and size of the field guide must be taken into account. Guides that do not have most of the birds on the National List can be a big hindrance.<br />
* It is a good idea to obtain two contrasting guides and compare them to see which one is easier to use.<br />
* Remember, you can tab your field guide (to facilitate navigation) and write in it (to add information). If you plan on writing in your guide, you should get a guide with lots of extra space on the pages.<br />
<br />
===Other books===<br />
Here is a list of other books that can aid you in studying. Each book has a link to its Amazon page.<br />
<br />
[http://www.amazon.com/Sibley-Guide-Bird-Life-Behavior/dp/1400043867/ref=pd_sim_b_7 The Sibley Guide to Bird Life & Behavior] As the companion guide to The Sibley Guide to Birds, this book is very helpful and easy to study from. The book is split into two sections: the first provides information about general ornithology, while the second includes more specific info about each family of bird. Both sections are very easy to read and understand. Strongly recommended. <br />
<br />
[http://www.amazon.com/Ornithology-Frank-B-Gill/dp/0716724154 Ornithology - Frank B. Gill]<br />
This is a college level textbook that contains lots of information about many topics in ornithology. It gets to be very in-depth and contains much more information than what you actually need in the competition, but it is a great resource for accurate information.<br />
<br />
==Introduction to Ornithology==<br />
===What is a bird?===<br />
Any creature in the class Aves is a bird. More specifically, birds are distinguished from other organisms by feathers which cover their body, bills, and often complex songs and calls. Birds are warm blooded and are bipedal with forearms adapted to be wings, though in some species the wings have become vestigial and can no longer be used for flight.<br />
<br />
Birds have one of the most efficient respiratory systems among vertebrates, and they lay eggs that are unique for their hard shell.<br />
<br />
There are around 10,000 known species of birds, which are found all over the earth, and on every continent. Birds occupy a large range of habitats, making them the most numerous tetrapod vertebrates.<br />
<br />
===Bird Anatomy===<br />
====Topography====<br />
Topography refers to the external anatomy of a bird.<br />
The diagrams below show the basic parts of a bird.<br />
<br />
[[Image:birdtopography.jpg|thumb|300px|center|This diagram shows the major features of a bird's body.]]<br />
[[Image:birdhead.jpg|thumb|300px|center|This diagram shows the major features of a bird's head.]]<br />
<br />
====Physiology====<br />
<br />
=====Respiration=====<br />
A bird's respiratory system is one of the most efficient found in vertebrates. This is mainly because of their ability to fly, which creates a need for more oxygen.<br />
<br />
Air sacks are structures unique to birds, which take up 20% of a bird's internal body space. Air sacks store air, keeping a fixed volume in the lungs. There are two types of air sacks: anterior and posterior. Sometimes, air sacks rest inside the semi-hollow bones of birds. In addition, a bird's lungs take up half of the space that mammal's lungs do, yet weight does not decrease.<br />
<br />
When a bird takes a breath, air passes through the trachea either into the bird's lungs and then the anterior air sacks or directly into the posterior air sacks. Air in the anterior air sacks go directly through the trachea and back out of the nostrils, while air in the posterior air sacks go through the lungs, and then through the trachea as the bird exhales.<br />
<br />
One important adaption birds have made is that new oxygen and old, waste gasses are never mixed during respiration. Also, old air is almost completely replaced by new air when a bird takes a breath.<br />
<br />
=====Circulation=====<br />
Like many mammals (including humans), birds have a four-chambered heart. However, a bird's heart can be almost twice the size of a mammal's, and much more efficient, for the same reason as the circulatory system. Powerful flyers and divers have the largest heart relative to their body size.<br />
<br />
=====Skeleton=====<br />
A bird's skeleton is, in many ways, well adapted for flight. The major bones of a bird's skeleton have a hollow interior with crisscrossing "struts" to provide support. Some bones contain air sacks which are used by the respiratory system. Bird skeletons generally follow a specific format, with the exception of extreme specialization.<br />
<br />
[[File:Birdwing.gif]]<br><br />
[[File:Bird skeleton.jpg|right|300px]]<br />
The image above shows the bones in the average bird's wing, with the left side being the tip of the wing and the right side being where it connects to the bird's body. Notice how similar it is to a human arm. There are two major sections to the arm. The upper arm is made up of the humerus, while the lower arm consists of the radius and the ulna. Birds have 2 wrist bones (carpals). However, instead of having 5 metacarpals (hand bones), they have one bone called the carpometacarpus. This limits the mobility of the manus, but it is better adapted for flight. Birds have 3 digits and 4 finger bones (phalanges, singular phalanx). The middle and largest digit has to phalanges.<br />
<br />
Birds' legs are slightly more complicated. What most people think of as the knees of a bird are actually the ankles, as the knees (and the upper legs (femur)) are mostly hidden by feathers. Birds have a fuse and extended foot bone (tarsometatarsus) which most people think of as the lower leg, and which give birds three sections to the leg instead of 2. The bone in the actual lower leg is the tibiotarsus, a fusion of part of the tarsus with the tibia. Birds have (at most) four toes, although some birds have less (e.g. the ostrich, which only has two toes. Refer to the image at the right for leg anatomy, and the image below for toe variations.<br />
<br />
{|<br />
|[[File:Toearrangements.gif|thumb|450px|left|a = anisodactyl, b = zygodactyl, c = heterodactyl, d = syndactyl, & e = pamprodactyl]]<br />
|}<br />
<br />
* Anisodactyl feet have three toes forward and one backward. It's the most common toe configuration, and is used by songbirds and perching birds.<br />
<br />
* Zygodactyl feet have two toes forward and two toes backward. It's used by climbers such as woodpeckers because it enables a stronger grip on branches.<br />
<br />
* Heterodactyl feet are similar to zygodactyl ones except the second toe is reversed. It's only found on trogons.<br />
<br />
* Syndactyl feet have the third and fourth toe partially fused together. It's characteristic of Kingfishers.<br />
<br />
* Pamprodactyl feet have all four toes facing front. Swifts may use this configuration to get a better grip when hanging on the sides of chimneys or caves.<br />
<br />
===Feathers and Plumage===<br />
====Feathers====<br />
Birds are the only modern animals that have feathers. Feathers are made of beta-keratin, which also makes up the scales on bird's legs.<br />
<br />
[[Image:contourfeather.jpg|thumb|200px|right|The major parts of a typical contour feather.]]<br />
Contour feather - Any of the outermost feathers of a bird, forming the visible body contour and plumage. A contour feather consists of a middle shaft and a vane on both sides of the shaft. The calamus, or quill, is the base of the shaft, while the rachis supports the vanes.<br />
<br />
The vane of a contour feather is mainly made up of barbs, which consist of rami (s. ramus) sticking out vertically from the rachis. Each ramus contains barbules, which in turn have interlocking barbicels. This gives the vane of a contour feather a tight, smooth surface.<br />
[[Image:featherlocking.png|thumb|400px|center|The barbs on a typical contour feather.]]<br />
<br />
Flight feathers - These feathers are only found on the wings and the tail. They are large, stiff, and aerodynamic, which is helpful in flight. There are three main types of flight feathers: primaries, secondaries, and tertiaries. In addition, feathers called coverts cover the bases of the flight feathers.<br />
<br />
Down feather - A feather that has plumulaceous barbs. It is mostly used for insulation. Down feathers do not have a rachis; barbs are attached directly to the quill.<br />
<br />
Semiplumes - Feathers with a long rachis and plumulaceous barbs. Like down feathers, semiplumes mainly provide insulation.<br />
<br />
Filoplumes - Small feathers with a long rachis, but only a few barbs at the top. Filoplumes are attached to nerve endings at the base, letting them send information to the brain about the placement of contour feathers.<br />
<br />
Bristles - Stiff feathers with some barbs found at the base. Bristles are almost always found on the face of birds. Bristles have many possible applications, including protection from insects and dust, and acting as a "net" to aid in catching insects.<br />
<br />
==Species of Birds==<br />
This section contains information about individual orders, families and species. The birds are in the same order as they are on the Official Bird List. Images of each bird, as well as comments on their identification, can be found at the page [[2011 Bird List]].<br />
<br />
*[[Ornithology/Anseriformes|Anseriformes]]<br />
*[[Ornithology/Galliformes|Galliformes]]<br />
*[[Ornithology/Gaviiformes|Gaviiformes]]<br />
*[[Ornithology/Podicipediformes|Podicipediformes]]<br />
*[[Ornithology/Procellariiformes|Procellariiformes]]<br />
*[[Ornithology/Pelecaniformes|Pelecaniformes]]<br />
*[[Ornithology/Ciconiiformes|Ciconiiformes]]<br />
*[[Ornithology/Falconiformes|Falconiformes]]<br />
*[[Ornithology/Gruiformes|Gruiformes]]<br />
*[[Ornithology/Charadriiformes|Charadriiformes]]<br />
*[[Ornithology/Columbiformes|Columbiformes]]<br />
*[[Ornithology/Cuculiformes|Cuculiformes]]<br />
*[[Ornithology/Strigiformes|Strigiformes]]<br />
*[[Ornithology/Caprimulgiformes|Caprimulgiformes]]<br />
*[[Ornithology/Apodiformes|Apodiformes]]<br />
*[[Ornithology/Trogoniformes|Trogoniformes]]<br />
*[[Ornithology/Coraciiformes|Coraciiformes]]<br />
*[[Ornithology/Piciformes|Piciformes]]<br />
*[[Ornithology/Passeriformes|Passeriformes]]<br />
<br />
==Bird Calls==<br />
{|class="sortable" style="text-align:center"<br />
|+Note: This chart includes all of the calls of the birds that are indicated for vocal identification on the National Bird List.<br />
!Order!!Family!!Species!!Common Name!!Link<br />
|-<br />
|Anseriformes||Anatidae||Cygnus buccinators||Trumpeter Swan||[http://www.mnbirdtrail.com/sounds/trumpet.wav Call]<br />
|-<br />
|Anseriformes||Anatidae||Anas platyrhynchos||Mallard||[http://macaulaylibrary.org/audio/137827 Call]<br />
|-<br />
|Galliformes||Phasianidae||Bonasa umbellus||Ruffed Grouse||[http://www.uwgb.edu/birds/wbba/species/audios/GROUSE__RUFFED.MP3 Call]<br />
|-<br />
|Galliformes||Phasianidae||Tympanuchus cupido||Greater Prairie-Chicken||[http://macaulaylibrary.org/audio/50136 Call]<br />
|-<br />
|Galliformes||Odontophoridae||Colinus virginianus||Northern Bobwhite||[http://macaulaylibrary.org/audio/105364 Call]<br />
|-<br />
|Gaviiformes||Gaviidae||Gavia stellata||Red-throated Loon||[http://macaulaylibrary.org/audio/132108 Call]<br />
|-<br />
|Ciconiiformes||Ardeidae||Botaurus lentiginosus||American Bittern||[http://macaulaylibrary.org/audio/53166 Call]<br />
|-<br />
|Falconiformes||Accipitridae||Haliaeetus leucocephalus||Bald Eagle||[http://www.allaboutbirds.org/guide/Bald_Eagle/sounds Call]<br />
|-<br />
|Falconiformes||Accipitridae||Buteo jamaicensis||Red-tailed Hawk||[http://fsc.fernbank.edu/Birding/bird_sounds/rtha.mp3 Call]<br />
|-<br />
|Gruiformes||Rallidae||Porzana carolina||Sora||[http://www.uwgb.edu/birds/wbba/species/audios/RAIL__SORA.MP3 Call]<br />
|-<br />
|Gruiformes||Gruidae||Grus americana||Whooping Crane||[http://macaulaylibrary.org/audio/2747 Call]<br />
|-<br />
|Charadriiformes||Charadriidae||Charadrius vociferus||Killdeer||[http://www.mbr-pwrc.usgs.gov/id/framlst/Song/h2730so.mp3 Call]<br />
|-<br />
|Charadriiformes||Scolopacidae||Bartramia longicauda||Upland Sandpiper||[http://www.uwgb.edu/birds/wbba/species/audios/SANDPIPER__UPLAND.MP3 Call]<br />
|-<br />
|Columbiformes||Columbidae||Zenaida asiatica||White-winged Dove||[http://macaulaylibrary.org/audio/45162 Call]<br />
|-<br />
|Columbiformes ||Columbidae ||Zenaida macroura||Mourning Dove||[http://www.uwgb.edu/birds/wbba/species/audios/DOVE__MOURNING.MP3 Call]<br />
|-<br />
|Cuculiformes||Cuculidae||Coccyzus erythropthalmus||Black-billed Cuckoo||[http://www.uwgb.edu/birds/wbba/species/audios/CUCKOO__BLACK_BILLED.MP3 Call]<br />
|-<br />
|Cuculiformes||Cuculidae||Geococcyx californianus||Greater Roadrunner||[http://macaulaylibrary.org/audio/8287 Call]<br />
|-<br />
|Strigiformes||Strigidae||Bubo virginianus||Great Horned Owl||[http://macaulaylibrary.org/audio/22873 Call]<br />
|-<br />
|Strigiformes||Strigidae||Strix varia||Barred Owl||[http://macaulaylibrary.org/audio/125371 Call]<br />
|-<br />
|Caprimulgiformes||Caprimulgidae||Nyctidromus albicollis||Common Pauraque||[http://identify.whatbird.com/obj/858/overview/Common_Pauraque.aspx Call]<br />
|-<br />
|Caprimulgiformes||Caprimulgidae||Caprimulgus carolinensis||Chuck-willâ€™s-widow ||[http://macaulaylibrary.org/audio/105213 Call]<br />
|-<br />
|Caprimulgiformes||Caprimulgidae||Caprimulgus vociferus||Whip-poor-will||[http://www.mbr-pwrc.usgs.gov/id/framlst/Song/h4170so.mp3 Call]<br />
|-<br />
|Coraciiformes||Alcedinidae||Megaceryle alcyon||Belted Kingfisher||[http://macaulaylibrary.org/audio/6562 Call] <br />
|-<br />
|Passeriformes||Tyrannidae||Contopus cooperi||Olive-sided Flycatcher|| [http://macaulaylibrary.org/audio/44937 Call] <br />
|-<br />
|Passeriformes||Tyrannidae||Myiarchus crinitus||Great Crested Flycatcher||[http://macaulaylibrary.org/audio/94314 Call]<br />
|-<br />
|Passeriformes||Tyrannidae||Tyrannus verticalis||Western Kingbird||[http://macaulaylibrary.org/audio/56905 Call]<br />
|-<br />
|Passeriformes||Vireonidae||Vireo gilvus||Warbling Vireo||[http://www.uwgb.edu/birds/wbba/species/audios/VIREO__WARBLING.MP3 Call]<br />
|-<br />
|Passeriformes||Vireonidae||Vireo olivaceus||Red-eyed Vireo||[http://www.allaboutbirds.org/guide/Red-eyed_Vireo/sounds Call]<br />
|-<br />
|Passeriformes||Corvidae||Cyanocitta cristata||Blue Jay||[http://macaulaylibrary.org/audio/49716 Call]<br />
|-<br />
|Passeriformes||Corvidae||Corvus brachyrhynchos||American Crow||[http://macaulaylibrary.org/audio/135436 Call]<br />
|-<br />
|Passeriformes||Corvidae||Corvus corax||Common Raven||[http://macaulaylibrary.org/audio/132161 Call]<br />
|-<br />
|Passeriformes||Paridae||Poecile carolinensis||Carolina Chickadee||[http://macaulaylibrary.org/audio/84821 Call]<br />
|-<br />
|Passeriformes||Paridae||Baeolophus bicolor||Tufted Titmouse||[http://macaulaylibrary.org/audio/94271 Call]<br />
|-<br />
|Passeriformes||Sittidae||Sitta canadensis||Red-breasted Nuthatch||[http://macaulaylibrary.org/audio/50328 Call]<br />
|-<br />
|Passeriformes||Troglodytidae||Catherpes mexicanus||Canyon Wren||[http://macaulaylibrary.org/audio/40607 Call]<br />
|-<br />
|Passeriformes||Turdidae||Hylocichla mustelina||Wood Thrush||[http://macaulaylibrary.org/audio/11316 Call]<br />
|-<br />
|Passeriformes||Turdidae||Turdus migratorius||American Robin||[http://macaulaylibrary.org/audio/94261 Call]<br />
|-<br />
|Passeriformes||Mimidae||Mimus polyglottos||Northern Mockingbird|| [http://macaulaylibrary.org/audio/94373 Call]<br />
|-<br />
|Passeriformes||Mimidae||Toxostoma rufum||Brown Thrasher||[http://macaulaylibrary.org/audio/94278 Call] <br />
|-<br />
|Passeriformes||Parulidae||Oporornis formosus||Kentucky Warbler||[http://macaulaylibrary.org/audio/94330 Call]<br />
|-<br />
|Passeriformes||Parulidae||Icteria virens||Yellow-breasted Chat||[http://www.allaboutbirds.org/guide/Yellow-breasted_Chat/sounds Call]<br />
|-<br />
|Passeriformes||Emberizidae||Pipilo maculatus||Spotted Towhee||[http://www.allaboutbirds.org/guide/Spotted_Towhee/sounds Call]<br />
|-<br />
|Passeriformes||Emberizidae||Zonotrichia querula||Harrisâ€™s Sparrow||[http://www.allaboutbirds.org/guide/Harriss_Sparrow/sounds Call]<br />
|-<br />
|Passeriformes||Cardinalidae||Cardinalis cardinalis||Northern Cardinal||[http://www.allaboutbirds.org/guide/Northern_Cardinal/sounds Call]<br />
|-<br />
|Passeriformes||Cardinalidae||Passerina cyanea||Indigo Bunting||[http://www.allaboutbirds.org/guide/Indigo_Bunting/sounds Call]<br />
|-<br />
|Passeriformes||Icteridae||Agelaius phoeniceus||Red-winged Blackbird||[http://www.allaboutbirds.org/guide/Red-winged_Blackbird/sounds Call]<br />
|-<br />
|Passeriformes||Icteridae||Sturnella neglecta||Western Meadowlark||[http://www.allaboutbirds.org/guide/Western_Meadowlark/sounds Call]<br />
|-<br />
|Passeriformes||Icteridae||Icterus galbula||Baltimore Oriole||[http://www.allaboutbirds.org/guide/Baltimore_Oriole/sounds Call] <br />
|}<br />
<br />
==FAQ==<br />
This section addresses questions which are commonly brought up by those who are new to the event.<br />
<br />
;Q - What field guide should I use? <br />
A - This depends on your personal preferences, as well as your strong and weak points. However, three of the main field guides seem to be the Sibley, Peterson, and NatGeo. The one recommended in the rules is Peterson's. It has very good illustrations and information on every bird on the national list. <br />
However, the Sibley guide has very good illustrations of the juvenile, male, and female birds. (So it is good for IDing birds) <br />
<br />
;Q - Are we allowed to bring two books and note sheets, or just one?<br />
A:You are allowed to bring one book and sheet of notes per person. That means a maximum of two per team.<br />
<br />
;Q - Are we only allowed to use field guides, or can we use other books instead?<br />
A - The rules say you may use any published books, so they do not have to be field guides. You might want to bring a few guides as backup just in case the event supervisors interpret that rule differently.<br />
<br />
;Q - Should I use Wikipedia as a resource?<br />
A - Wikipedia often has good, accessible information, but since it can be easily modified you should always cross reference with a more reliable source.<br />
<br />
==Glossary==<br />
{|class="sortable" style="text-align:center"<br />
|+A glossary of terms related to ornithology.<br />
!Word!!Definition<br />
|-<br />
|Altricial||When a hatchling is completely dependent on its parents.<br />
|-<br />
|Bird Topography||The external anatomy of birds; anatomical features that can be observed on the outside of a bird's body.<br />
|-<br />
|Contour Feather||Any of the outermost feathers of a bird, forming the visible body contour and plumage.<br />
|-<br />
|Down||A layer of fine feathers found under the tougher exterior feathers.<br />
|-<br />
|External Anatomy||See ''Bird Topography''<br />
|-<br />
|Feather (n)||Any of the light horny epidermal outgrowths that form the external covering of the body of birds and that consist of a shaft bearing on each side a series of barbs which bear barbules which in turn bear barbicels commonly ending in hooked hamuli and interlocking with the barbules of an adjacent barb to link the barbs into a continuous vane.<br />
|-<br />
|Feather (v)||To grow feathers.<br />
|-<br />
|Feather Tract||See ''pterylae''<br />
|-<br />
|Horns||Paired contour feathers arising from head.<br />
|-<br />
|Lower Mandible||The lower part of the bill.<br />
|-<br />
|Plumulaceous||Downy; bearing down.<br />
|-<br />
|Precocial||Hatching fully developed, ready for activity, not completely dependent on parents.<br />
|-<br />
|Pterylae||Areas of the skin from which feathers grow. <br />
|-<br />
|Upper Mandible||The upper part of the bill.<br />
|}<br />
<br />
A more detailed glossary can be found at Cornells Birds[http://www.birds.cornell.edu/education/educators/glossary/] and Manitoba Museum of Man and Nature Bird and Binder Page [http://www.virtualmuseum.ca/Exhibitions/Birds/MMMN/English/glossary_data.html]<br />
<br />
==Sample Questions and Answers==<br />
What is the difference between precocial and altricial young?<br />
<spoiler text="Answer"> Precocial youung are born with open eyes and down. They are capable of leaving the nest within 2 days of hatching. Altricial young are born with closed eyes and no down. They rely on parents for survival. All passerines are altricial. </spoiler><br />
<br />
What is the purpose of lobed feet? <spoiler text="Answer"> They allow birds to walk across marshes by increasing surface area, but provides more toe maneuverability than webbing. Coots and Grebes have lobed feet. </spoiler><br />
<br />
Describe three abilities that are unique to hummingbirds. <spoiler text="Answer"> Hummingbirds drink nectar, can hover and fly backwards, and their tiny legs and feet make them incapable of walking. </spoiler><br />
<br />
==Links==<br />
[http://soinc.org/sites/default/files/uploaded_files/Ornithology2010OfficialList7-16-09.pdf 2010 National Bird List]<br />
<br />
[http://www.allaboutbirds.org/ The Cornell Lab of Ornithology]<br />
<br />
[http://www.mbr-pwrc.usgs.gov/id/framlst/infocenter.html/ Patuxent Bird Identification InfoCenter]<br />
<br />
[http://people.eku.edu/ritchisong/externalanatomy.html Bird external anatomy -- good examples of bill characteristics]<br />
<br />
[http://en.wikipedia.org/wiki/Bird The Wikipedia article on birds]<br />
<br />
[http://www.audubon.org/net/link/index.html Audubon links -- scroll down to the ornithology section]<br />
<br />
[http://www.birds.cornell.edu/AllAboutBirds/birding123/identify/allaboutbirds_quiz Good practice game for identifying -- click "Choose Specific Birds" to pick which ones can appear in the quiz.]<br />
<br />
[http://www.sciencenc.com/event-help/ornithology.php The North Carolina state SciOly sight -- Has links to all bird calls you must know]<br />
<br />
{{Living ID}}<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Study Event Pages]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30558
Chemistry Lab/Electrochemistry
2014-04-05T22:34:48Z
<p>Voltage: </p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
The '''octet rule''' states that all atoms (excluding H and He) are trying to get an octet (8) electrons. H is trying to get either 2 or 0 electrons, and He already has 2.<br />
<br />
==Figuring Out Oxidation Numbers==<br />
<br />
When figuring out the oxidation number of an atom in a molecule, there are two simple rules to follow. <br />
<br />
'''1. The most electronegative atom gets the electron.''' <br /><br />
'''2. The oxidation numbers add up to the charge of the molecule'''. If you have a charge put it on the atoms which have not reached an octet of electrons. Change their oxidation number accordingly.<br />
<br />
Take the example of ethanol, <math>CH_3CH_2OH</math>.<br />
<br />
Number the C atoms. There is one on the left that will be called C1. There is another one in the middle that will be called C2.<br />
<br />
C1 has 3 bonds with H atoms. In each bond C1 is the more electronegative. So each of the 3 H atoms have an oxidation number of +1. So far C1's oxidation number is -3. C1 has another bond that is with C2. They each have the same electronegativity, so there is no change in their oxidation numbers. Thus, C1 has an oxidation number of -3.<br />
<br />
C2 so far has an oxidation number of 0 from the C1-C2 bond. It is also bonded to 2 H atoms, giving it an oxidation number of -2 and giving each of the H atoms an oxidation number of +1. Lastly, it has a bond with the O atom. O is more electronegative, so C2's oxidation number is -1.<br />
<br />
O so far has an oxidation number of -1 from the C-O bond. It is also bonded with an H atom. Since it is more electronegative, it gets the electron. Thus, the H atom has an oxidation number of +1, and O has an oxidation number of -2.<br />
<br />
Last but not least, add up all the oxidation numbers. All 6 of the H atoms have an oxidation number of +1. C1 has an oxidation number of -3. C2 has an oxidation number of -1. O has an oxidation number of -2.<br />
<br />
6(+1) -3 -1 -2 = 0<br />
<br />
This is the charge of ethanol, so the procedure has been completed.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Electrochemistry&diff=30557
Chemistry Lab/Electrochemistry
2014-04-05T22:08:07Z
<p>Voltage: /* Basic Information */</p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2011]] and [[2012]] foci of [[Chem Lab]].<br />
<br />
==Basic Information==<br />
A '''redox reaction''', or an oxidation/reduction reaction, occurs when one reactant is '''oxidized''', or loses electrons, and one reactant is '''reduced''', or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The '''oxidizing agent''' is reduced, and the '''reducing agent''' is oxidized.<br />
<br />
A '''half-reaction''' is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.<br />
<br />
The '''oxidation number''' of an atom in a molecule refers to the electrons being shared. If, in a covalent bond, it is basically "giving" an electron to the other atom, then that counts as a +1 on it's oxidation number. If, in a covalent bond, it is "taking" an electron from the other atom, then that counts as a -1 on it's oxidation number. Something that is important to realize is that it is not actually giving or taking an electron, that only occurs in ionic bonds, but that it or the other atom is getting the electron more often.<br />
<br />
==Balancing Oxidation/Reduction Reactions==<br />
Redox reactions follow a simple set of steps to solve.<br />
[[File:Redox rxn.gif|thumb|right|300px|A simple example of separating a reaction into half-reactions, balancing mass and charge, and combining the reactions.]]<br />
# '''Split it into 2 half-reactions'''. Usually, the basis of a redox reaction will be given with two compounds reacting to form two more compounds. Aside from oxygen and hydrogen, each reactant will have a corresponding element with a product. These two compounds will form one half-reaction; the other two form the other. Balance the coefficients of key compounds if necessary, i.e. Balancing Cr with Cr2O7. '''''Don't worry about balancing extra hydrogens or oxygens yet.'''''<br />
#'''Balance all non-hydrogen or oxygen elements'''. You may have balanced the key components of the half-reaction, but sometimes you'll have a pesky oxygen or hydrogen messing things up. To get this to balance, you must add ions to the other side to balance the reaction out. This process differs for acidic vs. basic solutions. Do '''NOT''' try to balance one equation with the other, this step '''ONLY''' comes at the end.<br />
#If it's in an '''acidic medium''':<br />
##'''Balance oxygen''' by adding H2O to the appropriate side. Add a coefficient to this H2O if necessary.<br />
##'''Balance hydrogen''' by adding H+ to the appropriate side. This can be on either side, depending on how many H2O's you added. Add a coefficient to this if necessary.<br />
##'''Balance the charge''' by adding electrons. Now you've balanced the equation in terms of elements, but the charge may not be balanced yet. To balance this, add electrons to the side with a higher charge until the total charge of each half of the half-reaction is the same.<br />
#If it's a '''basic medium'''<br />
##'''Balance oxygen''' as above.<br />
##'''Balance hydrogen'''. Instead of balancing this with H+, you need to balance it with OH-. This means that you may get extra oxygens. If this happens, add another H2O on the other side and continue adding OH- until it balances. There is also '''another method''' that is detailed below.<br />
##'''Balance the charge''' as above.<br />
#Now, we can add the reactions together to come up with our final reaction. '''Multiply each reaction by an integer''' so that there are the same number of electrons on each side (i.e. they cancel out). This means that the electrons of one half-reaction should be on the OPPOSITE side of the electrons in the other half-reaction. If this is not the case, go back and check your work. More than likely, there's a mistake in there somewhere.<br />
#Combine the half-reactions and cancel. The elctrons should cancel out completely, and H2O's and H+'s may cancel somewhat. If you have time, it's usually a good idea to make sure that the equation is balanced by elements and by charge.<br />
<br />
*'''Second method for balancing redox reactions in basic solution''': If it's in a basic medium, add OH- to each side of the final equation until all H+ is gone; then, cancel again. Remember that OH- + H+ ---> H2O in this step.<br />
<br />
==Activity Series==<br />
[[File:Activity series.gif|thumb|right|222px|An activity series.]]<br />
One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others. This activity series dictates what elements oxidize more easily than others. <br />
<br />
One of the most common ways that you will have to make an activity series in Chem Lab is through performing single replacement reactions by putting metal strips in a metal solution and seeing if there is a reaction. Each team will have a set of solutions and metals, and will have to perform each possible combination of metal to solution. A table can be formed recording which combinations result in reactions. The metal that reacts the most is the one that oxidizes the most easily, while the metal that does not react at all is the one that reduces the most easily. Once complete, the activity series should look similar to the one at right. If not, you likely made a mistake and should recheck your work.<br />
<br clear="all"/><br />
<br />
==Electrochemical Cells==<br />
Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.<br />
<br />
===Voltaic Cells===<br />
A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it. <br />
<br />
The cell in which oxidation occurs is called the '''anode''', and the cell in which reduction occurs is called the '''cathode'''. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.<br />
<br />
===Electrolytic Cells===<br />
Electrolytic cells use a current to decompose chemical compounds.<br />
<br />
==Electron Potential==<br />
<br />
==Links==<br />
*[http://youtu.be/yp60-oVxrT4 Tutorial about redox reactions]<br />
*[http://www.shodor.org/unchem/advanced/redox/index.html Succinct explanation of electrochem]<br />
<br />
[[Category:Chem Lab]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab&diff=30556
Chemistry Lab
2014-04-05T20:57:54Z
<p>Voltage: /* Chemistry Topics */</p>
<hr />
<div>{{EventLinksBox<br />
|active=yes<br />
|type=Chemistry<br />
|cat=Lab<br />
|2009thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=18&t=208 2009]<br />
|2009tests=[http://scioly.org/wiki/2009_Test_Exchange#Chemistry_Lab 2009]<br />
|2010thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=65&t=1282 2010]<br />
|2010tests=[http://scioly.org/wiki/2010_Test_Exchange#Chemistry_Lab 2010]<br />
|2011thread=[http://scioly.org/phpBB3/viewtopic.php?f=92&t=2206 2011]<br />
|2011tests=[http://scioly.org/wiki/2011_Test_Exchange#Chemistry_Lab 2011]<br />
|2012thread=[http://scioly.org/phpBB3/viewtopic.php?f=127&t=2949 2012]<br />
|2012tests=42<br />
|2013thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=142&t=3725 2013]<br />
|2013tests=2013<br />
|2014thread=[http://www.scioly.org/phpBB3/viewtopic.php?f=166&t=4953 2014]<br />
|2014tests=2014<br />
|C Champion=[[Troy High School (California)]]<br />
}}<br />
<br />
'''Chemistry Lab''' is an event where participants must learn the respective year's selected aspects of chemistry and perform a lab or a set of labs regarding those topics.<br />
<br />
Since this events rotates topics, each topic constitutes its own page. For topic-specific information, please see those pages, as this page only contains general information that applies to all topics.<br />
<br />
'''Past topics:'''<br />
{|class="wikitable" style="margin-top:0;"<br />
|-<br />
!Season<br />
!Topic(s)<br />
|-<br />
![[2006]]<br />
|[[Chem Lab/Thermodynamics|Thermodynamics]]<br />
|-<br />
![[2009]]<br />
|[[Chem Lab/Acids and Bases|Acids and Bases]], [[Chem Lab/Titration Race|Titration Race]]<br />
|-<br />
![[2010]]<br />
|[[Chem Lab/Kinetics|Kinetics]], [[Chem Lab/Aqueous Solutions|Aqueous Solutions]]<br />
|-<br />
![[2011]]<br />
|[[Chem Lab/Electrochemistry|Electrochemistry]], [[Chem Lab/Aqueous Solutions|Aqueous Solutions]]<br />
|-<br />
![[2012]]<br />
|[[Chem Lab/Electrochemistry|Electrochemistry]], [[Chem Lab/Periodicity|Periodicity]]<br />
|-<br />
![[2013]]<br />
|[[Chem Lab/Equilibrium|Equilibrium]], [[Chem Lab/Periodicity|Periodicity]]<br />
|-<br />
![[2014]]<br />
|[[Chem Lab/Equilibrium|Equilibrium]], [[Chemistry Lab#Stoichiometry|Stoichiometry]]<br />
|}<br />
<br />
==Description== <br />
*1 or 2 people per team.<br />
*[[Safety Glasses|Eye protection #4]].<br />
*Lab coat<br />
*50 minutes.<br />
*1 double-sided [[Note Sheet]]s (one per student)<br />
*Non-programmable, non-graphing calculator & pencil<br />
<br />
==Chemistry Topics==<br />
<br />
===Stoichiometry===<br />
<br />
The Merriam-Webster dictionary defines stoichiometry as "a branch of chemistry that deals with the application of the laws of definite proportions and of the conservation of mass and energy to chemical activity". Stoichiometry deals with calculations about the masses (sometimes volumes) of reactants and products involved in a chemical reaction. It is a very mathematical part of chemistry. The most common stoichiometric problem will present you with a certain amount of a reactant and then ask how much of a product can be formed. Ex:: <math>2A + 3B \to 3C</math>, Given 25 grams B and unlimited A how much C will be produced. This is called a mass-mass problem. These problems can be solved in 4 simple steps.<br />
<br />
#Make sure the chemical equation is correctly balanced.<br />
#Using the molar mass of the given substance, convert the mass given in the problem to moles.<br />
#Construct a molar proportion (two molar ratios set equal to each other) following the guidelines set out in other files. Use it to convert to moles of the unknown.<br />
#Using the molar mass of the unknown substance, convert the moles just calculated to mass.<br />
<br />
Other forms of stoichiometric problems are finding the limiting reactant and finding the percentage composition. You can find out more about these in the links below.<br />
<br />
The process is very similar when given gases (using the ideal gas law), solutions (using molarity) or molecules (using Avogadro's number)<br />
<br />
Stoichiometry can be approached in precisely the same way one would approach dimensional analysis. And, when in doubt, convert to moles.<br />
<br />
===Reaction Types===<br />
<br />
There are five main types of reactions (single displacement, double displacement, combustion, decomposition, and synthesis). Each of them has a specific form that they take. If you encounter problems dealing with reactions on the test, knowing the basic types can be very helpful because then you will be more likely to see the pattern and understand how to complete the reaction.<br />
<br />
====Single Displacement====<br />
[[File:Single replacement.JPG|thumb|right|300px|An example of a single replacement reaction. Here, copper reacts in silver nitrate solution to form copper nitrate solution and silver metal. The copper nitrate solution is visible since copper cations are blue in solution.]]<br />
<br />
Also called '''single replacement reactions'''. Single displacement reactions are oxidation-reduction reactions in which an element and a compound react to form another element and a compound. This reaction takes on the form<br />
<br />
<math>A + BC \to AC + B</math><br />
<br />
So the lone elemental reactant, A, forms a compound with C, forcing B out to become an element itself. In order for this to occur, A and B are usually metals that form a cation when compounded with C. <br />
<br />
The direction in which the reaction proceeds depends on each element's position in the [[Chem Lab/Electrochemistry#Activity Series|activity series]]. A has to be more likely to oxidize than B, because otherwise B will just simple stay in solution and A will remain untouched.<br />
<br />
====Double Displacement====<br />
Double displacement reactions are similar to single replacement, but they are usually not oxidation-reduction reactions. Instead of just one element being traded, double displacement reactions have two similarly formed compounds reacting to form other compounds.<br />
<br />
<math>AB + CD \to AD + CB</math><br />
<br />
This type of reaction is especially important in aqueous solutions, since most precipitation reactions are double displacement reactions. Precipitation occurs when AB and CD are both soluble in water, and when put together, either AD or BC is an insoluble compound and thus precipitates out of the solution. For more information about solubility, see [[Chem Lab/Aqueous Solutions]].<br />
<br />
====Combustion====<br />
Combustion reactions are redox reactions that produce fuel. Thus, combustion reactions are also exothermic reactions since they give off heat. The most common combustion reactions form carbon dioxide, water, and energy. For example, here is the combustion reaction for methane:<br />
<br />
<math>CH_4 + 2O_2 \to CO_2 + 2H_2O + energy</math><br />
<br />
Combustion can also occur with nitrogen instead of carbon. There is also combustion with only hydrogen and oxygen, and in this case only water forms as product.<br />
<br />
<math>2H_2 + O_2 \to 2H_20 + energy</math><br />
<br />
Since combustion reactions are among the most common exothermic reactions, it is a good idea to know the combustion reactions of several important compounds, or at least know how to go about finding it quickly. Since all of them have a similar form, you can guess what the products will be, which will make it easier. For example, for the combustion of a hydrocarbon in oxygen, the two products will be water and carbon dioxide, since the oxygen attaches itself to both carbon and hydrogen parts.<br />
<br />
====Decomposition====<br />
In decomposition, a compound decomposes into its constituent parts.<br />
<br />
<math>AB \to A + B</math><br />
<br />
This type of reaction usually occurs when the compound AB is unstable, since breaking a chemical bond requires energy. Since it takes energy to break a bond, the vast majority of decomposition reactions are endothermic.<br />
<br />
====Synthesis====<br />
Synthesis reactions are the opposite of decomposition reactions. These reactions have two elements or components bonding together to form a larger compound.<br />
<br />
<math>A + B \to AB</math><br />
<br />
Since this reaction forms a bond, it is exothermic.<br />
<br />
===Oxidation and Reduction===<br />
''Main article: [[Chem Lab/Electrochemistry]].''<br />
<br />
To remember Oxidation and Reduction just remember these simple acronym '''OIL RIG'''. Oxidation is Loss, Reduction is Gain. This is a simple way of remembering that whatever is oxidized loses electrons and whatever is Reduced gains electrons. The phrase '''LEO the lion says GER''' also works (Lose Electrons-Oxidation, Gain Electrons-Reduction)<br />
<br />
===Aqueous Solutions===<br />
''Main article: [[Chem Lab/Aqueous Solutions]].''<br />
<br />
An '''aqueous solution''' is a solution where the solute is dissolved in water.<br />
<br />
===Equilibrium===<br />
''Main article: [[Chem Lab/Equilibrium]].''<br />
<br />
===Periodicity===<br />
''Main article: [[Chem Lab/Periodicity]].''<br />
<br />
Periodicity refers to the pattern of physical and chemical properties in the [[Periodic Table|periodic table]]. These patterns are referred to as periodic trends. For example, one periodic trend is that the atomic radius of an element increases as one moves down a group, and leftward on a period.<br />
<br />
===Thermodynamics===<br />
''Main article: [[Thermodynamics]].''<br />
<br />
===Acids and Bases===<br />
''Main article: [[Chem Lab/Acids and Bases]]''<br />
<br />
===Titrations===<br />
''Main article: [[Chem Lab/Titration Race]]''<br />
<br />
==Event Strategy==<br />
Like all events, Chem Lab requires a strategy for you to be able to do your best.<br />
<br />
*It is very helpful if one or both partners has taken AP Chemistry, since some of the topics covered in this event are advanced and not covered in normal high school chemistry classes.<br />
*Try to split the work between you and your partner so that in studying, you can cover both topics.<br />
*If you get a longer test, ask if you can remove the staple and split the test, so that you can cover more of the test in less time.<br />
*Try to arrange your team so that you have one person who is good at quickly performing labs and one person who is good at computations and writing. This should facilitate the labs.<br />
*Make sure to work not just quickly, but efficiently, on the labs. Do them as quickly as you can, but if you end up with inaccurate results then going quickly didn't help you a whole lot. Also, do not take shortcuts unless you are absolutely, positively sure you can.<br />
*Make sure you have all of your protective equipment, as you may be disqualified if you do not have it.<br />
<br />
==Links==<br />
*[http://users.erols.com/merosen/stoichio.htm Stoichiometry links ]<br />
*[http://members.tripod.com/~Air_Piglet/ApChem.htm Study for the AP Chem test]<br />
*[http://www.chem.wisc.edu/~concept/ Some Chemistry tests ]<br />
*[[Media:Solubility_Rules.pdf|Solubility rules and evolved gases list for aqueous systems]]<br />
*[http://www.youtube.com/watch?v=jefaZdCy8fM&feature=related Chem lab video: oxidation/reduction]<br />
*[[Media:Inf flat Chem Notes.pdf|Infinity Flat's Chem Notes 1]]<br />
*[[Media:Inf flat Chem Notes 2.pdf|Infinity Flat's Chem Notes 2]]<br />
<br />
[[Category:Event Pages]]<br />
[[Category:Lab Event Pages]]<br />
[[Category:Needs Work]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Titration_Race&diff=30555
Chemistry Lab/Titration Race
2014-04-05T20:52:25Z
<p>Voltage: /* Titrations */</p>
<hr />
<div>==Titration Race (2009)==<br />
Despite the name of this portion of the [[2009]] [[Chem Lab]] event, this event can barely be considered a race. In fact, a recent rule clarification states that time will not be considered a tie-breaker at the national competition. However if time is considered, here are a few helpful hints to increase both your speed and accuracy in performing a titration.<br />
<br />
-Begin with a microtitration. For example titrate with 2 mL of the base to get a ballpark figure of the concentration. Use this to decide how much of the base you will use in the future trials. Remember that the more you use to titrate with, the more accurate your results will be.<br />
<br />
-Three trials are recommended. If the ask to show work for only 2 data points, still do three and show the two that are closest together UNLESS your first two seem so close that a third is unnecessary.<br />
<br />
-'''Remember''' what you're working with. Understand how sulfuric acid might change the calculations to find its concentration.<br />
<br />
-'''Do not overtitrate'''. This is what will seperate the teams the most. A healthy red color is not what you're looking for at the end of a titration. You are looking for your final solution to be barely tinged pink. If given paper, place it below your flask so that you can easily see ANY tinge of pink. If you do overtitrate, go back to the acid and add a drop or two to get to a good final point.<br />
<br />
==Acids and Bases==<br />
<br />
For more info on Acids and Bases, see [[Chem Lab/Acids and Bases]]<br />
<br />
==Titrations==<br />
<br />
Titrations are where acids and bases are mixed together to figure out some unknown quantity from multiple known quantities.<br />
<br />
===Titration Curves===<br />
<br />
Titration curves are a plot with the pH on the y-axis and the amount of acid (or base) added on the x-axis. They normally start out fairly flat. There is then a steep slope, and then more flatness.<br />
<br />
===Equivalence Point===<br />
<br />
The equivalence point is the point in a titration at which the amount of acid is equal to the amount of base. The steep slope in a titration curve is around the equivalence point.<br />
<br />
===End Point===<br />
<br />
The end point is the point in a titration at which the pH is 7.<br />
<br />
===Indicators===<br />
<br />
Indicators are an essential part of a titration. Indicators, when put in a solution, will change color depending on what the pH is. Indicators can be used to figure out when the equivalence point is reached. Indicator paper is paper with indicators mixed in. Universal indicator paper has a certain mix of indicators, making it so that from it's color you can tell the pH of a solution.<br />
<br />
{|class="sortable" style = "text-align:center"<br />
|+Different Indicators and Their pH Transition Ranges<br />
!!!Low pH color!!Transition pH Range!!High pH color<br />
|-<br />
|Gentian violet (Methyl violet 10B)||yellow||0.0-2.0||blue-violet<br />
|-<br />
|Malachite green (first transition)||yellow||0.0-2.0||green<br />
|-<br />
|Malachite green (second transition)||green||11.6-14||colorless<br />
|-<br />
|Thymol blue (first transition)||red||1.2-2.8||yellow<br />
|-<br />
|Thymol blue (second transition)||yellow||8.0-9.6||blue<br />
|-<br />
|Methyl yellow||red||2.9-4.0||yellow<br />
|-<br />
|Bromophenol blue||yellow||3.0-4.6||purple<br />
|-<br />
|Congo red||blue-violet||3.0-5.0||red<br />
|-<br />
|Methyl orange||red||3.1-4.4||yellow<br />
|-<br />
|Screened methyl orange (first transition)||red||0.0-3.2||grey<br />
|-<br />
|Screen methyl orange (second transition)||grey||3.2-4.2||green<br />
|-<br />
|Bromocresol green||yellow||3.8-5.4||blue<br />
|-<br />
|Methyl red||red||4.4-6.2||yellow<br />
|-<br />
|Azolitmin||red||4.5-8.3||blue<br />
|-<br />
|Bromocresol purple||yellow||5.2-6.8||purple<br />
|-<br />
|Bromothymol blue||yellow||6.0-7.6||blue<br />
|-<br />
|Phenol red||yellow||6.4-8.0||red<br />
|-<br />
|Neutral red||red||6.8-8.0||yellow<br />
|-<br />
|Naphtholphthalein||colorless to reddish||7.3-8.7||greenish to blue<br />
|-<br />
|Cresol Red||yellow||7.2-8.8||reddish purple<br />
|-<br />
|Cresolphthalein||colorless||8.2-9.8||purple<br />
|-<br />
|Phenolphthalein||colorless||8.3-10.0||fuchsia(pink)<br />
|-<br />
|Thymolphthalein||colorless||9.3-10.5||blue<br />
|-<br />
|Alizarine Yellow R||yellow||10.2-12.0||red<br />
|-<br />
|}<br />
<br />
[http://en.wikipedia.org/wiki/PH_indicator#Application Information from]<br />
<br />
===ICE Tables===<br />
<br />
ICE Tables are useful in titrations. They go something like this:<br />
<br />
{|class = "wikitable"<br />
|+ICE Table<br />
!!!<math>HA \to</math>!!<math>H^+</math> +!!<math>A^-</math><br />
|-<br />
|Initial||concentration||concentration||concentration<br />
|-<br />
|Change||-x||+x||+x<br />
|-<br />
|End||concentration||concentration||concentration<br />
|-<br />
|}<br />
<br />
===Henderson-Hasselbalch equation===<br />
<br />
<math>pH = pK_a + log_{10}\frac{[A^-]}{[HA]}</math><br />
<br />
===Strong Acid - Strong Base Titrations===<br />
<br />
Strong Acid-Strong Base titrations are relatively simple to work with. Normally they are used when you are trying the figure out the concentration of either a strong acid or base.<br />
<br />
Take a sample of the strong acid (or base). Measure and record the volume of it. Slowly start adding a strong base (or acid) for which you know the concentration. Find the equivalence point (the point at which the indicator should change color). Measure and record the volume of the strong base (or acid) needed to reach the equivalence point.<br />
<br />
At the equivalence point the amount of acid is equal to the amount of base. So, the following equation should be true.<br />
<br />
<math>M_aV_a = M_bV_b</math><br />
<br />
You know three of the variables and can solve for the fourth.<br />
<br />
===Weak Acid - Strong Base Titrations===<br />
<br />
Weak Acid-Strong Base titrations can be used to find the Ka of a weak acid. This can be used to identify the acid.<br />
<br />
Take a sample of the weak acid. Measure and record the volume of it. Add 10 ml of the strong base. Measure and record the pH with pH paper. Plot it on a titration curve graph. Add another 10 mL and do the same thing. Continue doing so. After you have done a fair amount, connect the dots with a line and estimate the pH of the equivalence point and the amount of strong base needed to get there. (the equivalence point is around the middle of the steep part of the titration curve)<br />
<br />
<math>M_aV_a = M_bV_b</math><br />
<br />
Where <math>V_b</math> is the concentration of strong base at the equivalence point.<br />
<br />
Calculate the concentration of the weak acid in the original solution. The concentration with the strong base added will be <math> \frac{M_aV_a}{V_a + V_b}</math>. Lets call this <math>M_e</math>. We know that <math>M_b</math> represents <math>[OH^-]</math> since the base is a strong base. Thus, <math>[OH^-] = \frac{M_bV_b}{V_a + V_b}</math>. Let's call this <math>M_{ih}</math>.<br />
<br />
{|class = "wikitable"<br />
|+ICE Table<br />
!!!<math>HA</math> +!!<math>OH^- \to</math>!!<math>A^- +</math>!!<math>H_2O</math><br />
|-<br />
|Initial||<math>M_e</math> M||<math>M_{ih}</math> M||0 M||~<br />
|-<br />
|Change||-x||-x||+x||~<br />
|-<br />
|End||<math>M_e</math> - x M||<math>M_{ih}</math> - x M||x M||~<br />
|-<br />
|}<br />
<br />
pH + pOH = 14 pOH = -log[<math>OH^-</math>] From the pH, calculate <math>[OH^-]</math>. Let's call this <math>M_{eh}</math>.<br />
<br />
<math> M_{eh} = M_{ih} - x </math><br />
<br />
Solve for x.<br />
<br />
<math> \frac{[H^+][A^-]}{[HA]} * \frac{1}{[H^+][OH^-]} = \frac{[A^-]}{[HA][OH^-]}</math><br />
<br />
<math> \frac{K_a}{K_w} = \frac{[A^-]}{[HA][OH^-]}</math><br />
<br />
<math> {K_a} = \frac{x*K_w}{(M_e - x)(M_{eh})}</math><br />
<br />
Solve for <math>K_a</math><br />
<br />
===Weak Base - Strong Acid Titration===<br />
<br />
A similar method to the Weak Acid-Strong Base titration is used for Weak Base-Strong Acid Titrations.<br />
<br />
[[Category:Chem Lab]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Titration_Race&diff=30554
Chemistry Lab/Titration Race
2014-04-05T20:52:07Z
<p>Voltage: Undo revision 30553 by Voltage (talk)</p>
<hr />
<div>==Titration Race (2009)==<br />
Despite the name of this portion of the [[2009]] [[Chem Lab]] event, this event can barely be considered a race. In fact, a recent rule clarification states that time will not be considered a tie-breaker at the national competition. However if time is considered, here are a few helpful hints to increase both your speed and accuracy in performing a titration.<br />
<br />
-Begin with a microtitration. For example titrate with 2 mL of the base to get a ballpark figure of the concentration. Use this to decide how much of the base you will use in the future trials. Remember that the more you use to titrate with, the more accurate your results will be.<br />
<br />
-Three trials are recommended. If the ask to show work for only 2 data points, still do three and show the two that are closest together UNLESS your first two seem so close that a third is unnecessary.<br />
<br />
-'''Remember''' what you're working with. Understand how sulfuric acid might change the calculations to find its concentration.<br />
<br />
-'''Do not overtitrate'''. This is what will seperate the teams the most. A healthy red color is not what you're looking for at the end of a titration. You are looking for your final solution to be barely tinged pink. If given paper, place it below your flask so that you can easily see ANY tinge of pink. If you do overtitrate, go back to the acid and add a drop or two to get to a good final point.<br />
<br />
==Acids and Bases==<br />
<br />
For more info on Acids and Bases, see [[Chem Lab/Acids and Bases]]<br />
<br />
==Titrations==<br />
<br />
Titrations are where acids and bases are mixed together to figure out some unknown quantity from multiple known quantities.<br />
<br />
===Titration Curves===<br />
<br />
Titration curves are a plot with the pH on the y-axis and the amount of acid (or base) added on the x-axis. They normally start out fairly flat. There is then a steep slope, and then more flatness.<br />
<br />
===Equivalence Point===<br />
<br />
The equivalence point is the point in a titration at which the amount of acid is equal to the amount of base. The steep slope in a titration curve is around the equivalence point.<br />
<br />
===End Point===<br />
<br />
The end point is the point in a titration at which the pH is 7.<br />
<br />
===Indicators===<br />
<br />
Indicators are an essential part of a titration. Indicators, when put in a solution, will change color depending on what the pH is. Indicators can be used to figure out when the equivalence point is reached. Indicator paper is paper with indicators mixed in. Universal indicator paper has a certain mix of indicators, making it so that from it's color you can tell the pH of a solution.<br />
<br />
{|class="sortable" style = "text-align:center"<br />
|+Different Indicators and Their pH Transition Ranges<br />
!!!Low pH color!!Transition pH Range!!High pH color<br />
|-<br />
|Gentian violet (Methyl violet 10B)||yellow||0.0-2.0||blue-violet<br />
|-<br />
|Malachite green (first transition)||yellow||0.0-2.0||green<br />
|-<br />
|Malachite green (second transition)||green||11.6-14||colorless<br />
|-<br />
|Thymol blue (first transition)||red||1.2-2.8||yellow<br />
|-<br />
|Thymol blue (second transition)||yellow||8.0-9.6||blue<br />
|-<br />
|Methyl yellow||red||2.9-4.0||yellow<br />
|-<br />
|Bromophenol blue||yellow||3.0-4.6||purple<br />
|-<br />
|Congo red||blue-violet||3.0-5.0||red<br />
|-<br />
|Methyl orange||red||3.1-4.4||yellow<br />
|-<br />
|Screened methyl orange (first transition)||red||0.0-3.2||grey<br />
|-<br />
|Screen methyl orange (second transition)||grey||3.2-4.2||green<br />
|-<br />
|Bromocresol green||yellow||3.8-5.4||blue<br />
|-<br />
|Methyl red||red||4.4-6.2||yellow<br />
|-<br />
|Azolitmin||red||4.5-8.3||blue<br />
|-<br />
|Bromocresol purple||yellow||5.2-6.8||purple<br />
|-<br />
|Bromothymol blue||yellow||6.0-7.6||blue<br />
|-<br />
|Phenol red||yellow||6.4-8.0||red<br />
|-<br />
|Neutral red||red||6.8-8.0||yellow<br />
|-<br />
|Naphtholphthalein||colorless to reddish||7.3-8.7||greenish to blue<br />
|-<br />
|Cresol Red||yellow||7.2-8.8||reddish purple<br />
|-<br />
|Cresolphthalein||colorless||8.2-9.8||purple<br />
|-<br />
|Phenolphthalein||colorless||8.3-10.0||fuchsia(pink)<br />
|-<br />
|Thymolphthalein||colorless||9.3-10.5||blue<br />
|-<br />
|Alizarine Yellow R||yellow||10.2-12.0||red<br />
|-<br />
|}<br />
<br />
[http://en.wikipedia.org/wiki/PH_indicator#Application Information from]<br />
<br />
===ICE Tables===<br />
<br />
ICE Tables are useful in titrations. They go something like this:<br />
<br />
{|class = "wikitable"<br />
|+ICE Table<br />
!!!<math>HA \to</math>!!<math>H^+</math> +!!<math>A^-</math><br />
|-<br />
|Initial||concentration||concentration||concentration<br />
|-<br />
|Change||-x||+x||+x<br />
|-<br />
|End||concentration||concentration||concentration<br />
|-<br />
|}<br />
<br />
===Strong Acid - Strong Base Titrations===<br />
<br />
Strong Acid-Strong Base titrations are relatively simple to work with. Normally they are used when you are trying the figure out the concentration of either a strong acid or base.<br />
<br />
Take a sample of the strong acid (or base). Measure and record the volume of it. Slowly start adding a strong base (or acid) for which you know the concentration. Find the equivalence point (the point at which the indicator should change color). Measure and record the volume of the strong base (or acid) needed to reach the equivalence point.<br />
<br />
At the equivalence point the amount of acid is equal to the amount of base. So, the following equation should be true.<br />
<br />
<math>M_aV_a = M_bV_b</math><br />
<br />
You know three of the variables and can solve for the fourth.<br />
<br />
[[Category:Chem Lab]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Titration_Race&diff=30553
Chemistry Lab/Titration Race
2014-04-05T20:29:39Z
<p>Voltage: </p>
<hr />
<div>==Titrations==<br />
<br />
Titrations are where acids and bases are mixed together to figure out some unknown quantity from multiple known quantities.<br />
<br />
===Titration Curves===<br />
<br />
Titration curves are a plot with the pH on the y-axis and the amount of acid (or base) added on the x-axis. They normally start out fairly flat. There is then a steep slope, and then more flatness.<br />
<br />
===Equivalence Point===<br />
<br />
The equivalence point is the point in a titration at which the amount of acid is equal to the amount of base. The steep slope in a titration curve is around the equivalence point.<br />
<br />
===End Point===<br />
<br />
The end point is the point in a titration at which the pH is 7.<br />
<br />
===Indicators===<br />
<br />
Indicators are an essential part of a titration. Indicators, when put in a solution, will change color depending on what the pH is. Indicators can be used to figure out when the equivalence point is reached. Indicator paper is paper with indicators mixed in. Universal indicator paper has a certain mix of indicators, making it so that from it's color you can tell the pH of a solution.<br />
<br />
{|class="sortable" style = "text-align:center"<br />
|+Different Indicators and Their pH Transition Ranges<br />
!!!Low pH color!!Transition pH Range!!High pH color<br />
|-<br />
|Gentian violet (Methyl violet 10B)||yellow||0.0-2.0||blue-violet<br />
|-<br />
|Malachite green (first transition)||yellow||0.0-2.0||green<br />
|-<br />
|Malachite green (second transition)||green||11.6-14||colorless<br />
|-<br />
|Thymol blue (first transition)||red||1.2-2.8||yellow<br />
|-<br />
|Thymol blue (second transition)||yellow||8.0-9.6||blue<br />
|-<br />
|Methyl yellow||red||2.9-4.0||yellow<br />
|-<br />
|Bromophenol blue||yellow||3.0-4.6||purple<br />
|-<br />
|Congo red||blue-violet||3.0-5.0||red<br />
|-<br />
|Methyl orange||red||3.1-4.4||yellow<br />
|-<br />
|Screened methyl orange (first transition)||red||0.0-3.2||grey<br />
|-<br />
|Screen methyl orange (second transition)||grey||3.2-4.2||green<br />
|-<br />
|Bromocresol green||yellow||3.8-5.4||blue<br />
|-<br />
|Methyl red||red||4.4-6.2||yellow<br />
|-<br />
|Azolitmin||red||4.5-8.3||blue<br />
|-<br />
|Bromocresol purple||yellow||5.2-6.8||purple<br />
|-<br />
|Bromothymol blue||yellow||6.0-7.6||blue<br />
|-<br />
|Phenol red||yellow||6.4-8.0||red<br />
|-<br />
|Neutral red||red||6.8-8.0||yellow<br />
|-<br />
|Naphtholphthalein||colorless to reddish||7.3-8.7||greenish to blue<br />
|-<br />
|Cresol Red||yellow||7.2-8.8||reddish purple<br />
|-<br />
|Cresolphthalein||colorless||8.2-9.8||purple<br />
|-<br />
|Phenolphthalein||colorless||8.3-10.0||fuchsia(pink)<br />
|-<br />
|Thymolphthalein||colorless||9.3-10.5||blue<br />
|-<br />
|Alizarine Yellow R||yellow||10.2-12.0||red<br />
|-<br />
|}<br />
<br />
[http://en.wikipedia.org/wiki/PH_indicator#Application Information from]<br />
<br />
===ICE Tables===<br />
<br />
ICE Tables are useful in titrations. They go something like this:<br />
<br />
{|class = "wikitable"<br />
|+ICE Table<br />
!!!<math>HA \to</math>!!<math>H^+</math> +!!<math>A^-</math><br />
|-<br />
|Initial||concentration||concentration||concentration<br />
|-<br />
|Change||-x||+x||+x<br />
|-<br />
|End||concentration||concentration||concentration<br />
|-<br />
|}<br />
<br />
===Henderson-Hasselbalch equation===<br />
<br />
<math>pH = pK_a + log_{10}\frac{[A^-]}{[HA]}</math><br />
<br />
===Strong Acid - Strong Base Titrations===<br />
<br />
Strong Acid-Strong Base titrations are relatively simple to work with. Normally they are used when you are trying the figure out the concentration of either a strong acid or base.<br />
<br />
Take a sample of the strong acid (or base). Measure and record the volume of it. Slowly start adding a strong base (or acid) for which you know the concentration. Find the equivalence point (the point at which the indicator should change color). Measure and record the volume of the strong base (or acid) needed to reach the equivalence point.<br />
<br />
At the equivalence point the amount of acid is equal to the amount of base. So, the following equation should be true.<br />
<br />
<math>M_aV_a = M_bV_b</math><br />
<br />
You know three of the variables and can solve for the fourth.<br />
<br />
===Weak Acid - Strong Base Titrations===<br />
<br />
Weak Acid-Strong Base titrations can be used to find the Ka of a weak acid. This can be used to identify the acid.<br />
<br />
Take a sample of the weak acid. Measure and record the volume of it. Add 10 ml of the strong base. Measure and record the pH with pH paper. Plot it on a titration curve graph. Add another 10 mL and do the same thing. Continue doing so. After you have done a fair amount, connect the dots with a line and estimate the pH of the equivalence point and the amount of strong base needed to get there. (the equivalence point is around the middle of the steep part of the titration curve)<br />
<br />
<math>M_aV_a = M_bV_b</math><br />
<br />
Where <math>V_b</math> is the concentration of strong base at the equivalence point.<br />
<br />
Calculate the concentration of the weak acid in the original solution. The concentration with the strong base added will be <math> \frac{M_aV_a}{V_a + V_b}</math>. Lets call this <math>M_e</math>. We know that <math>M_b</math> represents <math>[OH^-]</math> since the base is a strong base. Thus, <math>[OH^-] = \frac{M_bV_b}{V_a + V_b}</math>. Let's call this <math>M_{ih}</math>.<br />
<br />
{|class = "wikitable"<br />
|+ICE Table<br />
!!!<math>HA</math> +!!<math>OH^- \to</math>!!<math>A^- +</math>!!<math>H_2O</math><br />
|-<br />
|Initial||<math>M_e</math> M||<math>M_{ih}</math> M||0 M||~<br />
|-<br />
|Change||-x||-x||+x||~<br />
|-<br />
|End||<math>M_e</math> - x M||<math>M_{ih}</math> - x M||x M||~<br />
|-<br />
|}<br />
<br />
pH + pOH = 14 pOH = -log[<math>OH^-</math>] From the pH, calculate <math>[OH^-]</math>. Let's call this <math>M_{eh}</math>.<br />
<br />
<math> M_{eh} = M_{ih} - x </math><br />
<br />
Solve for x.<br />
<br />
<math> \frac{[H^+][A^-]}{[HA]} * \frac{1}{[H^+][OH^-]} = \frac{[A^-]}{[HA][OH^-]}</math><br />
<br />
<math> \frac{K_a}{K_w} = \frac{[A^-]}{[HA][OH^-]}</math><br />
<br />
<math> {K_a} = \frac{x*K_w}{(M_e - x)(M_{eh})}</math><br />
<br />
Solve for <math>K_a</math><br />
<br />
===Weak Base - Strong Acid Titration===<br />
<br />
A similar method to the Weak Acid-Strong Base titration is used for Weak Base-Strong Acid Titrations.<br />
<br />
[[Category:Chem Lab]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Titration_Race&diff=30552
Chemistry Lab/Titration Race
2014-04-05T16:28:21Z
<p>Voltage: </p>
<hr />
<div>==Titration Race (2009)==<br />
Despite the name of this portion of the [[2009]] [[Chem Lab]] event, this event can barely be considered a race. In fact, a recent rule clarification states that time will not be considered a tie-breaker at the national competition. However if time is considered, here are a few helpful hints to increase both your speed and accuracy in performing a titration.<br />
<br />
-Begin with a microtitration. For example titrate with 2 mL of the base to get a ballpark figure of the concentration. Use this to decide how much of the base you will use in the future trials. Remember that the more you use to titrate with, the more accurate your results will be.<br />
<br />
-Three trials are recommended. If the ask to show work for only 2 data points, still do three and show the two that are closest together UNLESS your first two seem so close that a third is unnecessary.<br />
<br />
-'''Remember''' what you're working with. Understand how sulfuric acid might change the calculations to find its concentration.<br />
<br />
-'''Do not overtitrate'''. This is what will seperate the teams the most. A healthy red color is not what you're looking for at the end of a titration. You are looking for your final solution to be barely tinged pink. If given paper, place it below your flask so that you can easily see ANY tinge of pink. If you do overtitrate, go back to the acid and add a drop or two to get to a good final point.<br />
<br />
==Acids and Bases==<br />
<br />
For more info on Acids and Bases, see [[Chem Lab/Acids and Bases]]<br />
<br />
==Titrations==<br />
<br />
Titrations are where acids and bases are mixed together to figure out some unknown quantity from multiple known quantities.<br />
<br />
===Titration Curves===<br />
<br />
Titration curves are a plot with the pH on the y-axis and the amount of acid (or base) added on the x-axis. They normally start out fairly flat. There is then a steep slope, and then more flatness.<br />
<br />
===Equivalence Point===<br />
<br />
The equivalence point is the point in a titration at which the amount of acid is equal to the amount of base. The steep slope in a titration curve is around the equivalence point.<br />
<br />
===End Point===<br />
<br />
The end point is the point in a titration at which the pH is 7.<br />
<br />
===Indicators===<br />
<br />
Indicators are an essential part of a titration. Indicators, when put in a solution, will change color depending on what the pH is. Indicators can be used to figure out when the equivalence point is reached. Indicator paper is paper with indicators mixed in. Universal indicator paper has a certain mix of indicators, making it so that from it's color you can tell the pH of a solution.<br />
<br />
{|class="sortable" style = "text-align:center"<br />
|+Different Indicators and Their pH Transition Ranges<br />
!!!Low pH color!!Transition pH Range!!High pH color<br />
|-<br />
|Gentian violet (Methyl violet 10B)||yellow||0.0-2.0||blue-violet<br />
|-<br />
|Malachite green (first transition)||yellow||0.0-2.0||green<br />
|-<br />
|Malachite green (second transition)||green||11.6-14||colorless<br />
|-<br />
|Thymol blue (first transition)||red||1.2-2.8||yellow<br />
|-<br />
|Thymol blue (second transition)||yellow||8.0-9.6||blue<br />
|-<br />
|Methyl yellow||red||2.9-4.0||yellow<br />
|-<br />
|Bromophenol blue||yellow||3.0-4.6||purple<br />
|-<br />
|Congo red||blue-violet||3.0-5.0||red<br />
|-<br />
|Methyl orange||red||3.1-4.4||yellow<br />
|-<br />
|Screened methyl orange (first transition)||red||0.0-3.2||grey<br />
|-<br />
|Screen methyl orange (second transition)||grey||3.2-4.2||green<br />
|-<br />
|Bromocresol green||yellow||3.8-5.4||blue<br />
|-<br />
|Methyl red||red||4.4-6.2||yellow<br />
|-<br />
|Azolitmin||red||4.5-8.3||blue<br />
|-<br />
|Bromocresol purple||yellow||5.2-6.8||purple<br />
|-<br />
|Bromothymol blue||yellow||6.0-7.6||blue<br />
|-<br />
|Phenol red||yellow||6.4-8.0||red<br />
|-<br />
|Neutral red||red||6.8-8.0||yellow<br />
|-<br />
|Naphtholphthalein||colorless to reddish||7.3-8.7||greenish to blue<br />
|-<br />
|Cresol Red||yellow||7.2-8.8||reddish purple<br />
|-<br />
|Cresolphthalein||colorless||8.2-9.8||purple<br />
|-<br />
|Phenolphthalein||colorless||8.3-10.0||fuchsia(pink)<br />
|-<br />
|Thymolphthalein||colorless||9.3-10.5||blue<br />
|-<br />
|Alizarine Yellow R||yellow||10.2-12.0||red<br />
|-<br />
|}<br />
<br />
[http://en.wikipedia.org/wiki/PH_indicator#Application Information from]<br />
<br />
===ICE Tables===<br />
<br />
ICE Tables are useful in titrations. They go something like this:<br />
<br />
{|class = "wikitable"<br />
|+ICE Table<br />
!!!<math>HA \to</math>!!<math>H^+</math> +!!<math>A^-</math><br />
|-<br />
|Initial||concentration||concentration||concentration<br />
|-<br />
|Change||-x||+x||+x<br />
|-<br />
|End||concentration||concentration||concentration<br />
|-<br />
|}<br />
<br />
===Strong Acid - Strong Base Titrations===<br />
<br />
Strong Acid-Strong Base titrations are relatively simple to work with. Normally they are used when you are trying the figure out the concentration of either a strong acid or base.<br />
<br />
Take a sample of the strong acid (or base). Measure and record the volume of it. Slowly start adding a strong base (or acid) for which you know the concentration. Find the equivalence point (the point at which the indicator should change color). Measure and record the volume of the strong base (or acid) needed to reach the equivalence point.<br />
<br />
At the equivalence point the amount of acid is equal to the amount of base. So, the following equation should be true.<br />
<br />
<math>M_aV_a = M_bV_b</math><br />
<br />
You know three of the variables and can solve for the fourth.<br />
<br />
[[Category:Chem Lab]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Aqueous_Solutions&diff=30538
Chemistry Lab/Aqueous Solutions
2014-04-05T12:19:48Z
<p>Voltage: </p>
<hr />
<div>{{Incomplete<br />
|event}}<br />
<br />
This page refers to the [[2011]] focus of [[Chem Lab]].<br />
<br />
<br />
This topic focused on the concentrations of solutions and how chemical properties of solutions are changed when mixed. This topic is very broad, considering that many substances used in chemistry are in aqueous form, including [[Chem Lab/Acids and Bases|Acids and Bases]], which are a slightly different focus.<br />
<br />
==Some General Concepts==<br />
<br />
===Moles===<br />
<br />
No, not the animal. A mole (abbreviate mol) is a number. Just like a dozen refers to the number 12, a mole refers to the number 6.022E23.<br />
<br />
The way scientists came up with this seemingly random number originated with elements and their molar masses. The mole is designed so that amu is the same thing as g/mol. This is useful if you want to figure out the number of atoms in a gram.<br />
<br />
===Equilibrium===<br />
<br />
Equilibrium is where the amount of reactant and the amount of product are not changing. For more info on equilibrium see [[Chem Lab/Equilibrium]]<br />
<br />
===Mixtures===<br />
<br />
====Solutions====<br />
<br />
Solutions are homogeneous (uniform) mixtures. For example: salt water.<br />
<br />
====Suspensions====<br />
<br />
Suspensions are heterogeneous (non uniform) mixtures. For example, dirt mixed in water. It is not uniform and the dirt will eventually settle to the bottom of the mixture.<br />
<br />
====Colloids====<br />
<br />
Colloids are heterogeneous (non uniform) mixures. For example, milk. It you take a close look at milk, you'll find it is composed of oil domains and water domains. The difference between colloids and suspensions is that colloids do not eventually settle out (with dirt in water the dirt will eventually settle to the bottom, but with milk the oil stays mixed with the water).<br />
<br />
==Components of a Solution==<br />
<br />
===Solute===<br />
<br />
The solute is what is being dissolved. For example, when dissolving salt in water, the salt is the solute.<br />
<br />
===Solvent===<br />
<br />
The solvent is what is dissolving the solute. For example, when dissolving salt in water, the water is the solvent.<br />
<br />
===Solution===<br />
<br />
A solution is the combination of a solute and a solvent.<br />
<br />
Because of the fact that in most solutions the amount of solute is relatively small compared to the amount of solvent, you may usually assume that the volume of solution is the same as the volume of solvent.<br />
<br />
==Solution Concentration==<br />
There are a number of ways to determine solute concentration.<br />
<br />
Concentration is typically expressed as [solute]. This expression means the concentration of the solute, usual expressed in terms of Molarity.<br />
<br />
===Molarity===<br />
<br />
Molarity or Molar concentration (abbreviated M) is equal to moles of solute over liters of solution.<br />
<br />
===Mass Concentration===<br />
<br />
Mass Concentration is equal to mass(g) of solute over volume(L) of solution. It is some ways similar to density, which is why it is abbreviated <math>\rho</math>.<br />
<br />
===Mole Fraction===<br />
<br />
Mole Fraction is equal to the moles of solute over the moles of solution.<br />
<br />
===Molality===<br />
<br />
Molality is equal to the moles of solute over kg of the solvent (not the solution).<br />
<br />
===Mass Fraction===<br />
<br />
Mass Fraction is similar to the Mole Fraction. It is the mass of the solute over the mass of the solution.<br />
<br />
===Mass Percentage===<br />
<br />
Mass Percentage is Mass Fraction times 100.<br />
<br />
===Parts Per Million (ppm)===<br />
<br />
Parts Per Million (abbreviated ppm) is Mass Fraction times 1,000,000.<br />
<br />
===Parts Per Billion (ppb)===<br />
<br />
Parts Per Billion (abbreviate ppb) is Mass Fraction time 1,000,000,000.<br />
<br />
===Conversion Between Units===<br />
<br />
===Molarity->Molality===<br />
<br />
Multiply by Liters of solution, divide by kilograms of solvent (approximately equal for dilute solutions).<br />
<br />
===Molality->Mass Percentage===<br />
<br />
Multiply by mass of solute, then divide by moles of solute, then multiply by kilograms of solvent, and divide by kilograms of solution (can be approximated by multiplying by molar mass).<br />
<br />
==Solubility Rules==<br />
There are certain rules that dictate which substances dissolve in water and which ones precipitate out.<br />
<br />
*Always dissolve<br />
**Nitrate (<math>NO_3^-</math>)<br />
**Acetate (<math>CH_3COO^-</math>)<br />
**Cations of alkali metals (e.g. sodium, potassium, etc.)<br />
*Sometimes dissolve<br />
**Sulfate (<math>{SO_4}^{2-}</math>)<br />
***Precipitates with barium, calcium, lead, silver, strontium and mercury (I)<br />
**Halides (except fluoride)<br />
***Precipitate with silver, lead, and mercury (I)<br />
**Sulfides<br />
*Rarely dissolve<br />
**Carbonates (<math>{CO_3}^{2-}</math>)<br />
**Hydroxides (<math>OH^-</math>)<br />
**Phosphates (<math>{PO_4}^{3-}</math>)<br />
<br />
==Solubility==<br />
<br />
===Equilibrium Constant===<br />
<br />
Take this reaction:<br />
<br />
<math>aA + bB \to cC + dD </math><br />
<br />
The equilibrium constant is equal to:<br />
<br />
<math>k=\frac{[C]^c * [D]^d}{[A]^a * [B]^b}</math><br />
<br />
Where all of the concentrations are the concentrations at equilibrium and where solids are excluded.<br />
<br />
For more info on the equilibrium constant, see [[Chem Lab/Equilibrium]].<br />
<br />
===Solubility Product Equilibrium Constant===<br />
<br />
The solubility product equilibrium constant (Ksp) is equal to<br />
<br />
<math>[A^+][B^-]</math><br />
<br />
for the following reaction:<br />
<br />
<math>AB \to A^+ + B^-</math><br />
<br />
===Unsaturated===<br />
<br />
Unsaturated solutions are solutions where the Ksp has not yet been reached.<br />
<br />
===Saturated===<br />
<br />
Saturated solutions are solutions where the Ksp has been reached.<br />
<br />
===Super Saturated===<br />
<br />
Super Saturated solutions are where the Ksp has been reached and gone over. These solutions can be achieved by heating up a solvent (heat causes the Ksp to increase), adding a solute, and then letting the solution cool.<br />
<br />
===Miscible===<br />
<br />
Two things are considered miscible when they can be mixed uniformly in any quantities.<br />
<br />
==Sample Questions==<br />
<br />
Questions in the kinetics section might involve...<br />
# Solution Concentration (Molarity, Molality, Mass Percentage, Parts Per Million)<br />
# Conversion Between Units (at state and national levels) <br />
# Determining Concentration using Density, Beer's Law or Titration<br />
# Freezing Point Depression and Boiling Point Elevation<br />
# Factors Affecting Solution Formation<br />
# Solubility<br />
<br />
[[Category:Chem Lab]]</div>
Voltage
https://scioly.org/wiki/index.php?title=Chemistry_Lab/Acids_and_Bases&diff=30537
Chemistry Lab/Acids and Bases
2014-04-05T12:03:49Z
<p>Voltage: /* Bases */</p>
<hr />
<div>{{Incomplete}}<br />
<br />
This page refers to the [[2009]] focus of [[Chem Lab]].<br />
==Acids and Bases (2009)==<br />
Acids and Bases is basically an acid/base titration lab. Be sure you know what a titration is, because it is not a good thing if you do not. This is a fairly quick and simple lab to complete, and it is more than worthwhile to double check your lab if you have enough materials. More repetitions of the lab can result in a more accurate answer. In a free-response style lab report, this might also get you some extra points for style and accuracy. Acid/base questions can range in difficulty from identifying if a solution was an acid based on its pH to balancing advanced reactions trying to find the acidic constant. In order to excel in this event you must be prepared for all levels.<br />
<br />
==Solutions==<br />
<br />
For more info on solutions see [[Chem Lab/Aqueous Solutions]]<br />
<br />
==pH and pOH==<br />
<br />
pH + pOH = 14<br />
<br />
===pH===<br />
<br />
pH is equal to the <math>-\log [H^+]</math> or <math>-\log [H_3O^+]</math>.<br />
<br />
===pOH===<br />
<br />
pOH is equal to the <math>-\log[OH^-]</math>.<br />
<br />
==Acids==<br />
<br />
All acids have a pH less than 7<br />
<br />
===Arrhenius Acids===<br />
<br />
Arrhenius Acids are defined to be chemicals that, when put in water, produce hydronium (<math>H_3O^+</math>) ions.<br />
<br />
===Bronsted-Lowry Acids===<br />
<br />
Bronsted-Lowry Acids are defined to be chemicals that donate protons (<math>H^+</math>). This is a broader definition than the Arrhenius definition because it does not have to involve water.<br />
<br />
===Lewis Acids===<br />
<br />
Lewis Acids are defined to be chemicals that accept electron pairs.<br />
<br />
===Strong Acids===<br />
<br />
Strong Acids are acids that pretty much completely disassociate in water. Some examples of Strong Acids are: <math>HI, HBr, HClO_4, HCl, HClO_3, H_2SO_4</math>, and <math>HNO_3 </math><br />
<br />
===Weak Acids===<br />
<br />
Weak Acids are acids that only partially disassociate in water. They have a Ka to define how much. Weak Acids consist of pretty much everything that is not a strong acid. For example: <math>HCOOH, CH_3COOH, HOOCCHOHCHOHCOOH,</math> and <math>{HSO_4}^-</math><br />
<br />
==Bases==<br />
<br />
All bases have a pH greater than 7.<br />
<br />
===Arrhenius Bases===<br />
<br />
Arrhenius Bases are defined to be chemicals that, when put in water, produce hydroxide (<math>OH^-</math>) ions.<br />
<br />
===Bronsted-Lowry Bases===<br />
<br />
Bronsted Lowry Acids are defined to be chemical that accept protons (<math>H^+</math>). This is a broader definition than the Arrhenius definition because it does not have to involve water.<br />
<br />
===Lewis Bases===<br />
<br />
Lewis Bases are defined to be chemicals that donate electron pairs.<br />
<br />
===Strong Bases===<br />
<br />
Strong Bases are bases that pretty much completely disassociate in water. Examples include <math>LiOH, NaOH, KOH, RbOH,</math> and <math>CsOH</math>.<br />
<br />
===Weak Bases===<br />
<br />
Weak Bases are bases that only partially disassociate in water. They have a Kb to define how much. A common example of a weak base is <math>NH_3</math>.<br />
<br />
==Equilibrium Constants==<br />
<br />
Take this reaction:<br />
<br />
<math>aA + bB \to cC + dD </math><br />
<br />
The equilibrium constant is equal to:<br />
<br />
<math>k=\frac{[C]^c * [D]^d}{[A]^a * [B]^b}</math><br />
<br />
Where all of the concentrations are the concentrations at equilibrium and where solids are excluded.<br />
<br />
For more info on equilibrium, see [[Chem Lab/Equilibrium]].<br />
<br />
===Acid Dissociation Constant===<br />
<br />
The acid equilibrium constant (Ka) is equal to<br />
<br />
<math>\frac{[H^+][A^-]}{[HA]}</math><br />
<br />
for the following reaction:<br />
<br />
<math>HA \to H^+ + A^-</math><br />
<br />
===Base Dissociation Constant===<br />
<br />
The base dissociation constant (Kb) is equal to<br />
<br />
<math>\frac{[BH^+][OH^-]}{[B]}</math><br />
<br />
for the following reaction:<br />
<br />
<math>B + H_2O \to BH^+ + OH^-</math><br />
<br />
===Dissociation Constant of Water===<br />
<br />
The dissociation constant of water (Kw) is equal to<br />
<br />
<math>[H^+][OH^-] = 1*10^{-14}</math><br />
<br />
for the following reaction:<br />
<br />
<math>H_2O \to H^+ + OH^-</math><br />
<br />
This is why pH + pOH = 14<br />
<br />
==Titrations==<br />
<br />
For more info on Titrations, see [[Chem Lab/Titration Race]].<br />
<br />
===Links===<br />
*Acid and base links [http://users.erols.com/merosen/acidbase.htm]<br />
<br />
[[Category:Chem Lab]]</div>
Voltage