Chemistry Lab

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

Focus for 2010: Kinetics and Aqueous Solutions.

Sample Questions: Kinetics
Questions in the kinetics section might involve...
 * 1) Reaction Rates
 * 2) Reaction Conditions (Temperature, Concentration, Particle Size, Cataylsts)
 * 3) Rate Laws
 * 4) Rate Constants (at state and national levels)

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

Acid & Bases
First of all, an old favorite, acids and bases. Last year in all 4 competitions I participated in (2 invitationals, regional, and states) this meant an acid/base titration lab. If you are not familiar with this lab, you will definitely want to ask a teacher to explain it to you before the competition. Believe me, I have seen a team ask the event coordinator what titrate means in the middle of the test, and he was not a happy person. This is a fairly quick and simple lab to complete and it is more than worth your while to DOUBLE CHECK YOUR LAB if you have enough materials. At the state level, I ran the lab through 4 times and averaged the very close results to come up with a more accurate overall result. In a free-response style lab report, this might also get you some extra points for style and accuracy. In the test, the acid/base questions ranged from difficulty of 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.

Titration Race
Despite the name of this portion of the 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.

-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.

-I would recommend three trials. 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.

-REMEMBER what you're working with. Understand how sulfuric acid might change the calculations to find its concentration.

-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.

Stoichiometry
Next, stoichiometry. I do not know what kind of questions this are 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.

Reactions
The last topic is 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.

Thermodynamics
This was the primary focus in a majority of 2005-2006 chem lab competitions. Thermodynamics is a very broad topic, so a variety of problems were used. Although basic enthalpy problems were sometimes found, entropy and Gibbs free energy were significantly more common, as they were more advanced topics.

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. It heps 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
 * Acid and base links
 * Upper level reaction links
 * Study for the AP Chem test
 * Some Chemistry tests
 * [[Media:Solubility_Rules.pdf|Solubility rules and evolved gases list for aqueous systems]]