Chemistry Lab: Getting The Volume Right!

Overview: In this experiment, you will be trying to fill a bottle with carbon dioxide gas that you generate from the reaction of a carbonate salt with an acid. Your objective is to come as close as possible to filling the bottle without "going over". To accomplish this, you will make use of stoichiometric relationships in a chemical reaction as well the gas laws

Procedure: This is pretty much a lab where you make up your procedure. There will be a number of carbonate salts available for your use, and some hydrochloric acid (of varying concentrations). If you want to test out what the reaction will look like with a given salt (something I do recommend!), you can try a small batch of salt + acid, but you will only get one shot at filling the bottle, so make sure you do all your theoretical work with great precision. The actual bottle-filling part will be done by all groups simultaneously near the end of the period. You will be allowed 3 minutes for your reaction to generate enough gas to fill the bottle. Even if your reaction is not finished in 3 minutes, you must take a reading at this time. Your apparatus should be set up so that it will fill the bottle on its own without being held or otherwise manipulated. Use clamps and other devices to make everything secure.

Grading: This lab is equal to a formal lab.

You will receive one grade for how well you did the experiment (this includes a good working apparatus: 5 points), and one grade for your write up. Grades for filling the bottle are as follows:

82 to 100% full (without going over) 5 points

65 to 81% full 4 points

40 to 64% full 3 points

25 to 39% full (points for going over) 2 points

less than 25% full 1 point

In addition, the group that is closest to 100% full (but not over) in each class will receive a 2-point bonus.

Important chemistry notes:

Your salt may be hydrated.

Carbon dioxide gas is somewhat soluble in water. (8.8 ml CO2 dissolves in 100 ml H₂Oat 20^oC)

Write-up instructions: On a separate sheet(s) of paper: (As always this write-up should be in your own words, especially different from your lab partner’s.)

Type out your procedure using numbered steps.
Draw a diagram of your apparatus.
Hand write your calculations and steps, clearly justifying the amount of reactants you used, and showing how much gas you predicted would form.
Summarize the components of your reaction in a table.
If you did not earn the full 5 points for your experimental volume of gas explain the cause(s) for your difference.
In the following story identify at least three major mistakes that Daryl Dingelhopfer made when performing his procedure. For each mistake, give a brief explanation for how his mistake might have influenced the results that he got.

Daryl used sodium carbonate as his salt of choice along with 2 M HCl. He determined how many moles of CO₂ he needed to fill his graduated cylinder since he knew that 22.4 L is the molar volume of any gas. He did not read the label on the bottle of sodium carbonate, but he did make a balanced equation and calculated his moles very precisely (to 3 decimal places!!). He determined that the molar mass of Na₂CO₃ was 82.99 g/mol. He weighed out the necessary grams of Na₂CO₃, and determined the correct volume of 2 M HCl solution he needed. He dissolved the sodium carbonate in about 300 ml of water. He then set up his gas collection apparatus with the appropriate tubing and an inverted graduated cylinder filled with water. When the cylinder-filling contest began, Daryl slowly added his HCl to the reaction flask, swirling constantly. Once all the acid was in the flask, he put on the stopper and started filling his cylinder. To his dismay, Daryl came in last place, with only 12 percent of his bottle filled with gas.