U1 Lab 4: Mass and Volume of a Gas
Purpose: to determine empirically the density of a gas.
Background: As seen in a prior lab, Alka-Seltzer dissolves in water and produces a gas (CO2). This
activity allows you to determine the density of the gas produced. The gas produced will be collected
by water displacement. The activity uses a collection apparatus that’s connected to a bottle filled
with water submerged in a pneumatic trough. Care must be taken not to spill any of the contents of
the tube before or after the gas is generated.
Materials: graduated cylinders, test tube, rubber stopper with bent-glass elbow and tubing, plastic
shoe box, collection bottle, ½ tablet Alka-Seltzer
Procedures:
1. Make a data table (LH page) to record:
a. mass of the “system” (beaker, test tube, water and Alkaseltzer) before and after the gas is produced
b. difference in mass of system.
c. volume of water in the collection bottle before and after
the gas is produced
d. difference in volume
2. Measure and record the maximum volume of water that the gas collection bottle can hold.
3. Fill the test tube ¼ full of water. Stand the test tube in the beaker to hold it steady. Mass the
beaker, test tube with water and the Alka-Seltzer (not in water yet). Record.
4. Turn the full collection bottle upside down in the water in the plastic shoe box without letting any
air into the bottle. Insert the end of the tubing into the bottle. This process may take a few
attempts.
5. Place the Alka-Seltzer into the test tube and quickly, quickly stopper it.
6. Allow the reaction to go to completion (how will you tell it has finished?).
7. Measure and record the mass of the beaker, test tube and water.
8. Under water, take the tube out of the collection bottle. Place your hand tightly over the mouth
of the bottle under water then turn the bottle right side up. Measure and record the volume of
water left in the bottle.
Analysis:
1. Calculate the density of the gas produced. Show all your work. (RH page)
2. Make a graph that shows the mass vs. volume lines for the materials from Lab 3 and the gas
produced in Lab 4. (LH page)
3. Make a data table to collect the class values for density of the gas. (LH page)
4. Make a histogram to show the spread of class values for gas density (LH page)
5. Draw particle diagrams (LH page) of the gas and the materials from Lab 3
Conclusion:
1. State the purpose of the lab.
2. Describe the range and central tendency of the class values for gas density. Describe how your
group’s value fits into that range. Include values with units from your data.
3. Compare the gas density to the density of the materials tested in Lab 3.
4. Describe how your graph shows these differences.
5. Explain how your particle diagrams show density differences.
6. Discuss at least 3 possible sources of error for this value (do NOT include measurement error or
calculation errors).