Measuring the Volume of Air and the Effect of Temperature: Experimental Procedures and Calculations

Experimental Measurement of Gas Volume and Temperature Effects

Assembly of the Apparatus

This experiment demonstrates how to measure the volume of air in a flask and observe the effect of temperature on gas volume. The setup involves a flask, stopper, glass tubing, and water bath.

• Apparatus: A 250 mL Erlenmeyer flask, a one-hole rubber stopper with a short piece of glass tubing, a 600 mL beaker, hot tap water, a wire gauze, an iron ring, and a heat source.

• Assembly Steps:

  1. Insert the glass tubing into the rubber stopper.

  2. Fit the stopper into the flask.

  3. Fill the beaker halfway with hot tap water.

  4. Support the beaker on a wire gauze and heat the water.

• Purpose: To prepare the system for measuring the volume of air at different temperatures.

Heating the Air in the Flask: Measuring the Higher Temperature

Heating the air in the flask allows observation of how gas volume changes with temperature, illustrating the principles of gas laws.

• Procedure:

  1. Place the stoppered flask in the 600 mL beaker and secure it with a utility clamp.

  2. Surround the flask with water as much as possible.

  3. Heat the water to boiling and boil gently for 5 minutes.

  4. Record the temperature of the boiling water using a thermometer.

• Key Temperatures:

  • Temperature of boiling water: 100°C

  • Temperature of cold water (for later steps): 23°C

• Volume Measurement: The volume of water entering the flask is used to determine the volume of air displaced.

• Example: If the volume of water entering the flask is 26.5 mL, this value is used in subsequent calculations.

Cooling the Air in the Flask: Measuring the Lower Temperature and Related Volume

Cooling the flask allows measurement of the volume of air at a lower temperature, further illustrating the relationship between temperature and gas volume.

• Procedure:

  1. Loosen the utility clamp and lower the end of the glass tubing into cold water.

  2. Remove the clamp and submerge the flask, with the glass tubing pointing downward.

  3. Keep the flask submerged for 5 minutes.

  4. At the end of this time, ensure the tubing end is submerged and the water level inside the flask matches the water level outside.

  5. Measure the volume of water that enters the flask, which corresponds to the volume of air displaced as the gas cools and contracts.

• Purpose: To observe the decrease in gas volume as temperature decreases, demonstrating Charles's Law.

Calculating the Volume of Air at Higher Temperatures

After the experiment, the volume of air in the flask is determined by measuring the volume of water that fills the flask after the air has been displaced.

• Procedure:

  1. Fill the flask with water and insert the stopper until its lower end is exactly at the water level.

  2. Ensure the glass tubing is filled with water.

  3. Remove the stopper and pour the water into a graduated cylinder to measure the volume.

• Note: The measured volume may be more than the value stamped on the flask due to the volume of the stopper and tubing.

Calculating Percent Error

Percent error is used to compare the experimental value to the calculated (theoretical) value, providing a measure of accuracy.

• Formula for Percent Error:

$\text{Percent error} = \frac{\text{experimental value} - \text{calculated value}}{\text{calculated value}} \times 100\%$

• Application: Use this formula to assess the accuracy of your experimental results compared to theoretical predictions.

Summary Table: Key Experimental Steps and Purposes

Step	Purpose
Assemble apparatus	Prepare system for gas volume measurement
Heat flask in boiling water	Measure gas volume at high temperature
Cool flask in cold water	Measure gas volume at low temperature
Measure water entering flask	Determine volume of air displaced
Calculate percent error	Assess experimental accuracy

Key Concepts and Definitions

• Charles's Law: The volume of a gas is directly proportional to its temperature (in Kelvin) at constant pressure.

• Percent Error: A quantitative measure of the accuracy of an experimental value compared to a theoretical value.

• Experimental Value: The value measured during the experiment.

• Calculated Value: The value predicted by theory or calculation.

Example Application: This experiment is commonly used in introductory chemistry labs to illustrate the relationship between temperature and gas volume, and to practice measurement and error analysis techniques.