Density of Carbon Dioxide
We will use the reaction of an antacid tablet with water to generate carbon dioxide. We will let the gas escape from the reaction tube and measure its volume after collecting the carbon dioxide by water displacement. We will determine the mass of gas produced by using the
Law of Conservation of Mass. Finally, we will determine the density of carbon dioxide gas.
Reaction:
This antacid is a mixture of powdered base (sodium bicarbonate) and powdered acid (citric acid). Aspirin (acetylsalicylic acid) is also present. When these substances come into contact in water, they react to produce carbon dioxide, water, sodium citrate, and sodium acetylsalicylate in solution according to the reaction:
NaHCO
3(aq)
+ H
3
C
6
H
5
O
7(aq)

H
2
O
(l)
+ CO
2(g)
+ NaH
7
C
6
O
7(aq)
The powdered base will also react with excess stomach acid to reduce the amount of acid in the stomach. The carbon dioxide bubbles show you that something is happening. They also help to agitate the other gases trapped in the stomach and thus aid in their release.
Materials:
 ¼ of antacid tablet

Erlenmeyer Flask

Stopper with glass bend inserted into hole, rubber tubing attached to glass bend



Pneumatic trough
Balance
Gas measuring tube and solid stopper
Procedure:
1.
Place 10 mL of water in the Erlenmeyer flask.
2.
Weigh the flask of water and ¼ tablet of antacid together. Keep the tablet piece dry.
3.
Fill the pneumatic trough with water. Be sure the water level is above the center bar of the trough.
4.
Fill the gas measuring tube with water. Place the solid stopper into the gas measuring tube.
5.
While holding the stopper, turn the gas measuring tube upside down into the pneumatic trough. Be sure the end of the tube is below water level. Remove the stopper while underwater.
6.
Clamp the gas measuring tube in place above the hole in the bottom of the pneumatic trough.
7.
Drop the tablet piece into the test tube and immediately put in the stopper that is attached to the glass bend and the rubber tubing.
8.
Collect the gas in the gas measuring tube by displacing the water.
9.
When the reaction is completed, measure the volume of the gas.
10.
Find the mass of the flask and contents.
Calculations: (Be sure to show all work, units, and appropriate significant figures.)
1.
Determine the mass of the CO
2
generated.
2.
Calculate the density of the gas.
3.
Use your experimentally determined density from #2 in the following calculations. Be sure to solve the problems using dimensional analysis.
a.
Under the same lab conditions, what volume of carbon dioxide would have a mass of 2.45g? b.
If you collected 0.75L of carbon dioxide under the same conditions as our lab, what would its mass in grams be?
Questions: (Answer these questions using complete sentences)
1.
Describe two physical change or physical property from this lab.
2.
Describe two chemical change or chemical property from this lab.
3.
Describe how a gas is collected by water displacement.
4.
How was the mass of the gas determined?
5.
What is the class average density of CO
2
?
6.
If a small bubble of air was trapped inside the gas measuring tube prior to the beginning of the lab, how would that change the value of each of the following? Be sure to state the change (increase, decrease or no effect) and explain your reasoning. a.
Original Mass of flask, water, and tablet b.
Volume of carbon dioxide collected c.
Final Mass of flask and its contents d.
Calculated Mass of carbon dioxide e.
Calculated Density of carbon dioxide
7.
If some of the carbon dioxide in our lab was dissolved in the water of the pneumatic trough how would that change the value of each of the following? Be sure to state the change (increase, decrease, or no effect) and explain your reasoning. a.
Original Mass of flask, water, and tablet b.
Volume of carbon dioxide collected c.
Final Mass of flask and its contents d.
Calculated Mass of carbon dioxide e.
Calculated Density of carbon dioxide