9: Molar Volume of a Gas
- Page ID
- 514171
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- To determine the molar volume of CO2 gas at room temperature.
- To use Dalton’s Law of Partial Pressures and the combined gas law to determine the molar volume of CO2 at STP.
INTRODUCTION
In this experiment, carbon dioxide gas will be generated from the thermal decomposition of sodium bicarbonate, NaHCO3. When solid sodium bicarbonate is heated, it decomposes into solid sodium carbonate, water vapor, and carbon dioxide gas. You will need to write a balanced chemical equation for this reaction.
You will heat a measured sample of sodium bicarbonate until the evolution of carbon dioxide is complete. The volume of carbon dioxide produced will be determined by measuring the volume of water displaced from a flask into a beaker. To complete the calculations in this lab, you will determine the theoretical moles of carbon dioxide evolved and use them to calculate the molar volume of carbon dioxide under laboratory room conditions.
Because the reaction produces water vapor and the gas is collected over water, water vapor will be mixed with the carbon dioxide gas in the collection flask. The experiment is designed so that the total pressure of the gas mixture (carbon dioxide and water vapor) equals atmospheric pressure, which you will measure using a laboratory barometer. The partial pressure of dry carbon dioxide in the flask can be calculated using Dalton’s Law of Partial Pressures. A chart of the vapor pressure of water as a function of temperature is provided at the end of the report sheet.
Once the pressure, volume, temperature, and moles of carbon dioxide have been established under room conditions, the combined gas law can be used to convert the gas volume to standard temperature and pressure (STP, 0 °C and 1.00 atm) and calculate the molar volume at STP.
The experimental apparatus is shown in Figure \(\PageIndex{1}\) in the procedure. The sample of sodium bicarbonate is placed in a hard-glass test tube connected to a water-filled flask. As carbon dioxide gas is generated, it displaces water from the flask into a beaker. The volume of water collected in the beaker is equal to the volume of gas generated at atmospheric pressure.
- 9.1: Molar Volume of a Gas - Experiment
- This page provides essential safety precautions and equipment necessary for a laboratory experiment on the thermal decomposition of sodium bicarbonate. It emphasizes wearing goggles and avoiding flammable materials near flames. The page includes a list of required items, detailed procedural steps for gas collection, and concludes with chemical waste disposal and cleaning instructions.
- 9.2: Molar Volume of a Gas - Pre-lab
- This page presents pre-lab questions for an experiment on the thermal decomposition of sodium bicarbonate (NaHCO3). It requires students to balance the chemical equation, explain Dalton’s Law of Partial Pressures for dry CO2 measurement, and emphasize the significance of equal water levels in experimental apparatus. Students must also calculate the partial pressure of dry CO2 from provided measurements and vapor pressure data.
- 9.3: Molar Volume of a Gas - Data and Report
- This page details an experimental procedure for measuring the molar volume of carbon dioxide produced from a sodium bicarbonate reaction. It includes data recording tables for variables like mass and temperature, key calculations for determining moles and theoretical CO2 volumes, and STP adjustments. The page concludes with post-lab questions exploring experimental errors, temperature effects on gas volume, and alternative measurement methods.