Determine the molar mass of CO2 experimentally
Purpose: to collect a sample of CO2 gas via water displacement, determine the number of moles of CO2
collected using Dalton’s Law of partial pressures and the Ideal Gas Law, and to determine the molar mass
of CO2.
The reaction you will be using:
aqueous acetic acid reacts with sodium bicarbonate to produce aqueous sodium acetate, water and
carbon dioxide gas.
Write the balanced equation for the reaction:
Before you do any of the experiment, think about the following…
 How will you calculate the number of moles of CO2 produced by the above reaction using the
apparatus shown and the ideal gas law and Dalton’s Law of partial pressures?
o Remember that you are collecting gas over water. You must consider the vapor pressure of
water.
 How you will you obtain the mass of CO2 produced, as you will need this to calculate molar mass?
 How many trials of your experiment should you do?
Things you need to know:
1. Once you have collected your gas, BEFORE you determine the volume in the cylinder, you need to
lower/raise the graduated cylinder so that the water in the cylinder is at the same level as the
water in the tub. This ensures that the pressure of the gas in the tube is equal to the atmospheric
pressure.
2. You will need to look up the barometric pressure since we don’t have a barometer.
3. You will need to take the temperature of the water.
Procedure:
1. Set up the apparatus as shown by the teacher.
2. Weight out 1.00 g sodium bicarbonate into a tin foil boat.
3. Put about 100 mL of vinegar into a plastic bottle.
4. weigh the bottle, vinegar, and the baking soda in the boat all on the scale to get a total mass before
the reaction.
5. Carefully put the boat into the vinegar and float it on top without spilling it.
6. Place the lid to the apparatus onto the plastic bottle.
7. Now shake the bottle to mix the vinegar and baking soda.
8. Collect the gas until no more gas can be collected.
9. Determine the volume of CO2 gas collected.
10. Determine the mass of the CO2 gas collected.
11. Determine the number of moles of CO2 collected (don’t forget that you collected it over water…)
12. Determine the molar mass of the CO2 from the experimental data.
13. Calculate the actual molar mass of CO2 and calculate your percent error.
Lab Write Up:
Include all of the following:
 Your objective for this lab.
 The balanced equation for the reaction.
 A sketch of the apparatus.
 A data table with all trials and average of the trials.
 Your calculation for determining the number of moles of CO2 collected
 Your calculation for determining the mass of CO2 collected.
 Your calculation for determining the molar mass of CO2 from the data.
 Your calculation for determining your percent error.