Chemistry Lab

Past topics:

Description
1 or 2 people per team. Eye protection #4. 50 minutes. Non-programmable, non-graphing calculator & pencil (NO reference material).

Sample Questions: Aqueous Solutions
Questions in the kinetics section might involve...
 * 1) Solution Concentration (Molarity, Molality, Mass Percentage, Parts Per Million)
 * 2) Conversion Between Units (at state and national levels)
 * 3) Determining Concentration using Density, Beer's Law or Titration
 * 4) Freezing Point Depression and Boiling Point Elevation
 * 5) Factors Affecting Solution Formation
 * 6) Solubility

Stoichiometry
I do not know what kind of questions this will bring but I can explain a little about this $5 term. 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:: 2A + 3B ---> 3C, 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.


 * 1) Make sure the chemical equation is correctly balanced.
 * 2) Using the molar mass of the given substance, convert the mass given in the problem to moles.
 * 3) 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.
 * 4) Using the molar mass of the unkown substance, convert the moles just calculated to mass.

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.

Stoichiometry can be approached in precisely the same way one would approach dimensional analysis. And, when in doubt, convert to moles.

Reactions
This is a very generic area so you will have to wait until sample problems come out in the rule book to see what will be on the test. Most problems will probably involve balancing reactions so that the products equal the reactants. You will definitely want to know the five main types of reactions (single displacement, double displacement, combustion, decomposition, and synthesis). Caution: Because this is a very open topic many test makers, especially at the regional level, might take it upon themselves to use questions that you may never have seen before. Just try your best and understand that if you have been diligently studying and haven't seen it, chances are neither have the other teams.

Oxidation and Reduction
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)

More information about this can be found out in Chem Lab/Electrochemistry.

Aqueous Solutions: Solution Concentration

 * Molarity=(number of moles of solute)/(Liters of solution)
 * Molality=(number of moles of solute)/(kilograms of solvent)
 * Mass Percentage=massA/(massA+massB+...)
 * Parts Per Million=Mass Percentage*10,000

Aqueous Solutions: Conversion Between Units

 * Molarity->Molality: Multiply by Liters of solution, divide by kilograms of solvent (approximately equal for dilute solutions).
 * Molality->Mass Percentage: 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 appromimated by multiplying by molar mass).

Strategy
One last thing I would like to mention is strategy. There is a strategy involved all events and I will reveal some hints on a good strategy for this event. First off, don't try to learn everything by yourself. You have a partner for a reason; use him/her/it. It helps if you divide up the study load so that you can learn more in depth in the topics. Next, if the test is extremely long, divide it up. There is no reason for two people to be working on the same problem that one person could do. Lastly, it often helps to have one person do the lab while another starts the test. This saves you valuable time if there is a long test, or allows you to put extra effort into careful practice knowing you are not pressed for time.

Links

 * Stoichiometry links
 * Study for the AP Chem test
 * Some Chemistry tests
 * [[Media:Solubility_Rules.pdf|Solubility rules and evolved gases list for aqueous systems]]
 * Chem lab video: oxidation/reduction