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Investigating the Self-Inflating Balloon Mark as Favorite (43 Favorites)

LAB in Gas Laws, Stoichiometry, Mole Concept. Last updated May 16, 2019.

Summary

In this lab, students will investigate the chemical reaction used in the self-inflating balloon. They will apply their knowledge of gas laws and stoichiometry in order to determine the quantities of reactants used to inflate the balloon.

Grade Level

High School

NGSS Alignment

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

  • HS-PS1-7: Use mathematical representation 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

  • Calculate moles of a gas given temperature, volume, and pressure.
  • Convert between units of temperature.
  • Convert between units of pressure.
  • Determine mass of a substance from its mole value.
  • Apply stoichiometric concepts relating quantities of chemicals in a reaction.

Chemistry Topics

This lab supports students’ understanding of

  • Chemical Reactions
  • Stoichiometry
  • Gas Laws
  • Endothermic and Exothermic Reactions

Time

Teacher Preparation: ten minutes

Lesson: 45-60 minutes

Materials (per lab group)

  • 1000 ml beaker
  • Self-inflating balloons (available from many online sources, often called “Whack-A-Pack”)
  • Thermometer
  • Electronic scale
  • Local Air Pressure Data

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Do not consume lab solutions, even if they’re otherwise edible products.

Teacher Notes

  • The hands-on portion of the lab activity can be completed by students in 15-20 minutes. Most of the calculations and questions can be done within an additional 30-45 minutes (or completed for homework).

  • Note that some balloons do not inflate completely and others take as long as five minutes to fully inflate, so having a few spares is a good idea.
  • It helps to have one balloon “dissected” ahead to time to show students the aqueous citric acid pouch and the powdered sodium bicarbonate (NaHCO3). The mass of sodium bicarbonate from the dissected balloon will be needed for an error calculation.
  • If you have enough balloons, students can cut one open with scissors and do this themselves. The contents are shown in the photograph.
  • The “pouch” has the dissolved citric acid and the sodium bicarbonate is the white powder. It can easily be weighed.
  • In my experience the balloon typically inflates to 200-300 ml, which is roughly 0.011 moles of NaHCO3, or about 0.9 grams. For comparison, a balloon sample contained 1.1 grams of NaHCO3 (which is within 20% error).
  • Calculation for "expected mass" of NaHCO 3 in balloon, using a sample I had which had a volume of 260 ml at 22°C and a pressure of 1.01 atm.
  • Using the equation below, there is 1 mole of CO 2 per mole of NaHCO3 so there are 0.011 moles of NaHCO3 x 86.1 g/mole = 0.95 grams of NaHCO 3 expected to be in the balloon.
    C6H8O7 (aq) + 3 NaHCO3 (s) → Na3C6H5O7 (aq) + 3 H2O (l) + 3 CO2 (g)
  • The % error for this calculation would be:
  • In reality the pressure in the balloon is probably a bit greater than atmospheric pressure and since reaction goes to completion, this is the largest source of error.
  • Any pressure unit can be used, so long as students have the corresponding value of “R” in the ideal gas law, PV=nRT.
  • An alternative calculation would be to weigh the sodium bicarbonate in a balloon, assume it is the limiting reactant and calculate the moles and then pressure of carbon dioxide produced.
  • A complete answer key is included for teacher reference.

For the Student

Lesson

Background

In this lab, you will investigate the reaction that occurs within the self-inflating balloon. This is a reaction that occurs between citric acid and sodium bicarbonate, to produce carbon dioxide gas as one of the products.

Prelab Questions

  1. What is the equation for the ideal gas law?
  2. What is the conversion between °C and K?
  3. Balance the equation that will occur:
  4. What are some common uses of citric acid (C 6H8O7) and sodium bicarbonate (NaHCO3)?

Objective

Determine the mass of sodium bicarbonate and citric acid used to inflate the balloon.

Materials:

  • Self-inflating balloon
  • 1000 ml beaker
  • Thermometer
  • Electronic Scale

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.
  • Do not consume lab solutions, even if they’re otherwise edible products.
  • Food in the lab should be considered a chemical not for consumption.

Procedure

  1. Your teacher will demonstrate the proper technique for inflating the balloon.
  2. When you inflate a balloon with your group you should hear some evidence that the reaction is making a gas and you should notice a temperature change (it is safe to hold the balloon in your hand once it has inflated) that will tell you something about the nature of the reaction.
  3. When the balloon has fully inflated you need to measure the volume of the balloon. Use the beaker, room temperature tap water and the water displacement method to find the volume of your balloon.
  4. Pay close attention to the markings on the beaker as they will guide you in knowing to what level of precision you should record the volume. (Example: if the lines are placed every 1ml, I should estimate to the nearest 0.1ml).
  5. Record the volume of the balloon in the data table.
  6. Using room temperature water, you can assume the water temperature and room temperature are the same. Record the temperature value in the data table.
  7. Determine (look it up, or provided by teacher) the atmospheric pressure in the classroom (convert the value if necessary to an appropriate unit such as mmHg, kPa or atm). We will assume that the pressures inside and outside the balloon are equal. Record this value, as well as any conversions you completed, in the data table.

Data

Observations:
Temperature of balloon during reaction
(was it hot or cold to the touch?)
Volume of Balloon:
Show calculation from displacement
Temperature (°C):
Also record temperature value in Kelvin
Pressure:
Locate value from weather site or teacher
Mass of NaHCO3 in “dissected” balloon:
Value provided from teacher

Calculations

Record all work clearly. Pay attention to units and significant figures.

  1. Convert your temperature value to Kelvin.
  2. If needed, convert your pressure value to an appropriate unit, as instructed by your teacher.
  3. Convert the volume of your balloon to L.
  4. Calculate the number of moles of CO2 gas in the balloon.
  5. Calculate the number of moles of NaHCO3 that reacted in the balloon.
  6. Calculate the mass

Analysis

Calculate your percent error between the actual mass of NaHCO3 in the balloon (as measured by your teacher or your group) and the calculated mass determined in question 6. Show work.

Extension Questions

Answer the following questions related to this lab:

  1. Suppose you took your balloon with you to a variety of environments:
    1. You go to Denver, where the temperature is -4°C and the air pressure is 0.91 atm. What volume will your balloon have there?
    2. You go the Death Valley where the air pressure is 791 mm Hg and the temperature is 43°C. What volume will your balloon have there?
    3. If you took your balloon up in a hot air balloon where the temperature was 5°C and the air pressure was 95 kPa, what volume would your balloon have there?
  2. Calculate the mass of citric acid that was in the balloon (we can’t weigh that as it was dissolved in water.) Show all work.
  3. Describe at least two ways to provide evidence that the solution in the little plastic pouch is in fact an acid.
  4. If your balloon was filled with the same number of moles of a gas such as Helium, would the volume be the same, more, or less? Explain.
  5. Was the reaction endothermic or exothermic? What evidence do you have to support this?

Conclusion

Based on your data, summarize the mass of each reactant needed to inflate the balloon to the volume you obtained. Could you have dissolved the NaHCO3 in water in the “pouch” and had the citric acid as a powder? Why or why not?