Laboratory Techniques I, CHY 114
Chemistry Department, University of Southern Maine

What is wrong with this picture???*

Molar Volume:
What's the Volume of a Mole of Oxygen?

The experimental procedure of this experiment is adapted from The Molar Volume of Dioxygen and Other Gases, from Chemistry in the Laboratory, James M. Postma, Julian L. Roberts, Jr., and J. Leland Hollenberg, New York: W.H. Freeman and Company, 2000.

Assignment

In your classroom text, read the chapter on gases. Pay special attention to

  • units of gas pressure, including inches of mercury and torr,
  • ideal gas behavior, including Boyle's and Charles's laws,
  • partial pressures and the behavior of gas mixtures, and
  • pressure of water vapor at various temperatures

In Laboratory Handbook, see Table 5, p. 109, which gives the vapor pressure of water (although it does not say water) at various temperatures. You will need this table (or one like it) to complete your report on this experiment.

Goals

  1. To measure the volume and the mass of a sample of oxygen gas
  2. To calculate from these data the volume of a mole of oxygen gas under standard temperature and pressure (STP).

Overview

To reach your goal in this lab, you will run a chemical reaction that produces oxygen (O2, properly -- but rarely -- called "dioxygen"). This gas is lost from the reaction vessel, so you measure its mass by weighing the reaction vessel before and after the reaction. You measure the volume of the gas by seeing how much water the gas pushes out of a bottle as the gas emerges from the reaction vessel. Finally, you use ideal gas laws to find the volume that this gas would occupy at standard temperature and pressure.

Oxygen gas is produced by the the decomposition of hydrogen peroxide (H2O2) into water and oxygen. The reaction is catalyzed by an enzyme in yeast. To run this reaction, you will mix aqueous H2O2 with a suspension of baker's yeast in water.

Preparing for Lab

The following problems require calculations similar to those called for in the report on this experiment. Learn how to work these problems, showing your calculations with units. For problems requiring calculations, answers are provided. Similar questions may appear on your prelaboratory quiz. For guidance, look at the procedures that follow, and at the Assignment/Report Form for this experiment.

  1. *What is wrong with the picture above? Answer: Where are the safety glasses!!!
  2. Balance the following equation, which describes the reaction you will use to produce oxygen gas:
    1. H2O2 (aq) ----> H2O (l) + O2 (g)
  3. Polly Ester, a CHY114 student, goes to an online weather service to learn today's atmospheric pressure. The reported pressure is 29.362 inches of mercury. Polly needs to know the pressure in torr (mm of mercury). Convert 29.362 in. Hg to torr. Answer: 745.79 torr.
  4. Using the method of this experiment, Polly produces 355 mL of oxygen gas at a temperature of 28.5 C on a day when the atmospheric pressure is 745.8 torr. What would be the volume of this gas at standard temperature (0.0 C) and pressure (760 torr)? Answer: 315 mL.
  5. Polly also finds that her reaction vessel weighs 0.451 g less after the reaction than before.
    a) What mass of O2 did Polly produce? Answer: 0.451 g
    b) How many moles of O2 did Polly produce? Answer: 0.0141 mol
  6. If a 0.0141-mol sample of O2 has a volume of 315 ml at STP, what is the volume of a mol of O2 at STP? Answer: 22,300 mL/mol
  7. Do Polly's results fit your expectations, or do they surprise you? Explain.

Procedures

Download and print the Procedure for this experiment. Study it carefully after reading this page. It's a good idea to translate the procedure into step-by-step instructions for your lab work. Bring the printed procedure and your instructions with you to lab. Once per semester, you might earn a free perfect quiz score for bringing good translated instructions.

Report

Download and print the Report Form for this experiment. Bring it with you to lab.

If it is not convenient for you to visit this page online, you might want to print it out as well.

CHY114 Lab Manual