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Ideal Gas Law Mark as Favorite (63 Favorites)

LAB in Gas Laws, Percent Yield, Stoichiometry, Dimensional Analysis, Measurements, Error Analysis. Last updated May 09, 2024.

Summary

In this lab, students use the reaction of an antacid table with water to inflate a balloon. They then use the ideal gas law to determine the number of moles of gas produced by the reaction.

Grade Level

High school

AP Chemistry Curriculum Framework

This lab supports the following units, topics and learning objectives:

  • Unit 1: Atomic Structure and Properties
    • Topic 1.1: Moles and Molar Mass
      • SPQ-1.A: Calculate quantities of a substance or its relative number of particles using dimensional analysis and the mole concept.
  • Unit 3: Intermolecular Forces and Properties
    • Topic 3.4: Ideal Gas Law
      • SAP-7.A: Explain the relationship between the macroscopic properties of a sample of gas or mixture of gases using the ideal gas law.
  • Unit 4: Chemical Reactions
    • Topic 4.1: Introduction for Reactions
      • TRA-1.A: Identify evidence of chemical and physical changes in matter.

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

  • HS-PS1-7: Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
  • Scientific and Engineering Practices:
    • Using Mathematics and Computational Thinking
    • Analyzing and Interpreting Data

Objectives

By the end of this lab, students should be able to

  • Use the ideal gas law to calculate the number of moles in a sample of gas.
  • Calculate the mass of a known volume of gas.

Chemistry Topics

This lab supports students’ understanding of

  • Gas laws
  • Ideal Gas Law
  • Stoichiometry
  • Percent Yield
  • Error Analysis
  • Dimensional Analysis
  • Measurement

Time

Teacher Preparation: 15 minutes

Lesson: 40-80 minutes

Materials

For each group:

  • Alka-Seltzer tablets (up to three per group)
  • Balloon
  • 10- mL graduated cylinder
  • Stopwatch
  • Length of string
  • Meter stick
  • Thermometer

Safety

  • Always wear safety goggles when working with chemicals in a laboratory setting.
  • Students with latex allergies should not handle balloons.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Students should wash their hands thoroughly before leaving the lab.

Teacher Notes

  • Even if students have a difficult time tying the balloon, make sure they have pinched off the opening as soon as the reaction begins.
  • To find the atmospheric pressure, you can either have students look up the barometric pressure from a weather report, use a barometer, or use the accepted value for atmospheric pressure if resources are unavailable.
  • The pressure in the data table is in kPa. Students will need to use dimensional analysis to convert this to atm. The conversion factor is 1 atm = 101.3 kPa. Students may also need to convert barometric pressure from mmHg to kPa. (1 kPa = 7.5 mmHg)
  • Verify the antacid tablets you use have the same quantity of sodium bicarbonate per tablet (1,916mg is listed in the student procedure). If the quantity is different, make sure to update the value in the lab
  • Students will need to subtract the partial pressure of the water vapor from the atmospheric pressure to obtain the pressure of the carbon dioxide, CO2 produced. Assuming the pressure of the balloon is equal to the atmospheric pressure:
    • Patm = PCO2 + PH2O
  • They will use Dalton’s Law of partial pressures. The Vapor Pressure of Water Wikipedia page can be used to find the PH2o at the temperature of the lab room.
  • Students will need to make sure that the units for volume, temperature, and pressure are in the correct units. Since R = 0.08206 L atm/mol K, the units for volume will be liters (L), the unit for pressure will be atmospheres (atm), and the unit for temperature will be Kelvin (K).
  • Extension: Students can consider the volume of water they used; would changing the amount of water effect the results of the experiment?

For the Student

Lesson

Purpose

  1. Measure and record pressure, volume, and temperature data for a gas sample.
  2. Use the ideal gas law to determine the amount of gas in a sample.
  3. Compare an amount of gas produced with the predicted amount.

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.
  • If you have a latex allergy, do not touch the balloons and tell your teacher immediately.

Materials

  • Antacid tablets (your teacher will pass out a specific amount to each group)
  • Balloon
  • 10-mL graduated cylinder
  • Stopwatch
  • String
  • Meter stick
  • Thermometer

Background

When an Alka seltzer tablet is added to water, the baking soda and citric acid in the tablet dissolve into the solution and react with each other. In this lab, you will use the ideal gas law to determine how much CO2 gas will be produced.

The equation for the reaction is shown below:

  • H3C6H5O7(aq) + 3 NaHCO3(aq) --> 3H2CO3(g) + Na3C6H5O7(aq)
  • citric acid + baking soda --> carbonic acid + sodium citrate

The carbonic acid will break down into water and carbon dioxide, so the final chemical formula will be:

  • H3C6H5O7(aq) + 3 NaHCO3(aq) --> 3 H2O(l) + 3 CO2(g) + Na3C6H5O7(aq)
  • citric acid + baking soda --> water + carbon dioxide + sodium citrate

Procedure

  1. Blow up the balloon a little bit, then let the air out—this makes it easier for the balloon to inflate later. Record the number of antacid tablets given to you by your teacher in data table two. Break the tablet(s) into pieces small enough to fit into the balloon and push them inside.
  2. With the balloon still deflated, use the graduated cylinder to add 10 mL of water to the balloon, then quickly close and tie the balloon. It is critical to work quickly when tying the balloon!
  3. Shake the balloon to mix the contents. Start the timer as soon as you have finished mixing them. Gently swirl the contents every so often.
  4. Measure and record the circumference of the balloon in data table one every two minutes. To measure, wrap the string around the balloon and note how far the string wrapped around the balloon. Use the meter stick to measure the length of the string that wrapped around the balloon. When the circumference does not change between measurements, you may stop the timer, and stop measuring. 
  5. When you have time, check the weather online for the current pressure and in the classroom. Use a thermometer to determine the temperature of the classroom. Record these values in data table two. Convert the temperature to Kelvin, and record this in data table two as well. (1 degree Celsius = 274.15 Kelvin)

Data

Data Table 1: Circumference of Balloon
Time (min)

Circ. (cm)

Data Table 2: Gas Sample Data
Number of tablets Pressure (kPa)
Temperature (°C) Temperature (K)
Volume (cm3) Volume (L)

Calculations

Show your work.

  • Use the maximum circumference to calculate the volume of the balloon. Since the balloon is nearly spherical, use the formula for a sphere:
  • Convert this volume from cm3 to L and record this value in data table two.
  • Assume that the balloon is at the same temperature and pressure as the room. The balloon not only contains carbon dioxide gas, but also contains water vapor. The following equation can be used to determine the pressure of the CO2 to use in the ideal gas law.

Patm = PCO2 + PH2O

Look up the partial pressure of water using a vapor pressure of water table. Then, solve the equation for the partial pressure of CO2.

    • Use the ideal gas law to calculate how many moles of gas are in the balloon. Record it in the data table below.

    PV=nRT (where R=0.08206 L•atm/mol•K)

    • Given the following equation for the reaction that took place in the balloon, what is the identity of the gas in the balloon?
      H3C6H5O7(aq)  +  3 NaHCO3(aq)  → 3 H2O(l)  +  3 CO2(g)  +  Na3C6H5O7(aq)
    • Use the number of moles of gas you calculated in the balloon to determine the mass of that gas in the balloon; this is stoichiometry! Record the mass in the data table below.
    • On the Antacid tablet box, it claims that each tablet contains 1,916 mg of NaHCO3 and 1,000 mg of H3C6H5O7. Given that amounts of NaHCO3 and H3C6H5O7 per tablet, calculate the mass of the gas (see question 5) that will be produced if each tablet completely reacts. This is also stoichiometry! Record it in the data table below. Hint: Remember to determine the limiting reactant!
    • Calculate the percent yield: Record it in the data table below.
    • Calculate the percent error. How does this measurement differ from percent yield?
    Gas amount (mol)
    Actual mass of gas (g) – from PV=nRT Theoretical mass of gas (g) – from stoichiometry
    Percent yield
    Percent error

    Conclusion

    1. On the board, record in the data table:
      1. How many tablets you had.
      2. The maximum volume, in L.
      3. The actual mass of gas.
      4. Your percent error.
    2. Compare your results with those of the other groups. For example, a group with two tablets should have twice the volume and mass of gas as a group with one tablet. Describe how the results compare between groups and propose explanations for any discrepancies.