The Molar Volume of Gases

Purpose

• Determine the molar volume of a gas.

Learning Objectives

• Quantitatively measure the volume of oxygen gas produced from hydrogen peroxide decomposition.
• Calculate the molar volume of oxygen gas at standard temperature and pressure (STP) using the ideal gas law and Dalton's law of partial pressures.

Principles

Molar Volume of an Ideal Gas

• Molar volume: volume of one mole of a substance (L/mol).
• Varies with temperature and pressure.
• Calculated from density and molar mass.
• At STP (0°C and 1 atm), molar volume ≈ 22.4 L/mol.
• Avogadro’s Law: For a gas at constant temperature and pressure, volume is proportional to moles of gas.
• Boyle’s Law: Volume inversely proportional to pressure at constant temperature.
• Charles’ Law: Volume increases with temperature at constant pressure.
• Ideal Gas Law: PV = nRT.

Experiment Overview

• Determine molar volume of oxygen at STP using the decomposition of hydrogen peroxide:
  • Reaction: 2 H₂O₂ (aq) → 2 H₂O (l) + O₂ (g).
  • Catalyst: FeCl₃ used to speed up the reaction.
• Measure volume of O₂ produced and calculate molar volume.

Equipment & Chemicals

• Small test tubes for FeCl₃ catalyst.
• Deionized water, 3% hydrogen peroxide solution, 3 M iron(III) chloride solution.

Safety

• Wear safety glasses.
• Flush skin with water if chemicals spill.

Procedure

1. Assemble apparatus (Figure 3.1).
2. Test apparatus for leaks.
3. Measure 20 mL of 3% H₂O₂ and pour into the flask.
4. Weigh flask A before reaction.
5. Conduct reaction, measure and record volume of O₂ produced.
6. Measure temperatures in flasks and record.
7. Obtain barometric pressure data.
8. Dispose of waste properly.

Calculations

• Calculate mass and moles of O₂.
• Determine volume of O₂ at STP using collected data.
• Compare calculated molar volume to the actual value (22.4 L/mol).

Review Questions

1. Discuss the role of FeCl₃ in the reaction.
2. Analyze how oxygen dissolving in water affects molar volume calculation.
3. Consider effects of errors (e.g., wet flask) on results.
4. Calculate molar mass based on given conditions.
5. Discuss real vs ideal gas behavior.
6. Explain discrepancies in molar volumes of CO₂ and HCl compared to the ideal.
7. Calculate conditions required for producing gas and effects on plant growth.

Lab Report Guidance

• Summarize data and results.
• Discuss possible sources of error and their impacts on results.
• Propose solutions to identified errors.

Preparation for Next Experiment

• Complete pre-lab assignments and quizzes.

Appendix

• Table of vapor pressures of water at various temperatures.