Materials Included In Kit

Additional Materials Required

Prelab Preparation

Create a model balloon for students out of a plastic bag. Best prepared the day of, an hour or more before class time.

1. Obtain a plastic bag and decorate it, using permanent markers (see Figure 1 in the Procedure for ideas).
2. Note: The mass of reactants needed is dependent on the pressure and temperature of the room and the volume of the bag. The plastic bags included in the kit have an approximate volume of 0.560 L.
3. Read the temperature and pressure of the room using a thermometer and barometer.
4. Convert the units of pressure to atm if necessary.
5. Convert the units of temperature to units of Kelvin if necessary.
6. Use the ideal gas law to solve for the number of moles CO₂ needed. See Lab Hints for example calculations.
7. Note: The numbers used will be different if your room pressure and temperature are different than 24 °C and 1 atm.
8. For a room at approximately 24.0 °C and a pressure of 1 atm, measure and place 1.93 g of sodium bicarbonate into the bag.
9. Measure and place 1.61 g of solid citric acid monohydrate in the bag.
10. Cut the long stem off of the pipet included in the kit (see Figure 2 in the Procedure).
11. Fill the pipet full with water and gently place it in the plastic bag so it is upright and will not spill into the solids.
12. Seal the bag—removing as much air as possible.
13. Transparent tape can be used around the edges to prevent leaking (see Figure 3 in the Procedure).
14. Shake the bag. DO NOT squeeze the bag.

15. Present students with one of the self-inflating balloons.
16. Pass it around, let students look at it and record their observations (remind students not to activate the balloon).
17. Activate the balloon by pressing on the water packet inside. Shake.
18. Pass the self-inflating balloon around so students can feel that the balloon is cold. Allow students to shake the balloon. They can also listen and hear the reaction occurring inside.
19. Have students record their observations on the worksheet.
20. Display the premade plastic bag balloon for students to see.
21. Go over tips on making the plastic bag balloon. For example, how to tape the bag to secure it from leaking.

Safety Precautions

Citric acid, sodium bicarbonate and the contents of the self-inflating balloon may be irritating to skin, and especially irritating to the eyes. Avoid contact of all chemicals with eyes and skin and wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Solutions may be rinsed down the sink. Leftover solid sodium bicarbonate and citric acid may be placed in the trash, according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. All parts of this laboratory activity can reasonably be completed in two 50-minute class periods. The Prelaboratory Qustions may be completed before coming to lab.
• Long forceps work best for removing the citric acid/water packet, such as Flinn Catalog No. AB1093.
• Students can use a large graduated cylinder to record the volume of the balloon and plastic bag or students can use a smaller graduated cylinder multiple times to record the volume.
• The mass of chemicals needed is dependent on the pressure and temperature of the room. To prepare the sample plastic bag balloon ahead of time, calculate the amount of chemicals needed based on the room’s conditions.
• To take the pressure of the room, have students read from a barometer. If a barometer is not available, check the local weather stations for the pressure in the area. Note: Barometric pressure from a weather station is not the actual pressure, but has been adjusted for sea level. If the pressure is not given in atms, have the students convert the pressure to atms (1 inch = 2.54 cm, 10 mm = 1 cm, 1 atm = 760 mm Hg = 101.3 kPa = 14.6959 psi).
• Temperature needs to be in Kelvin for the ideal gas law calculations (K = °C + 273.15).
• Let students know that the solid citric acid used in the lab is citric acid monohydrate with a formula mass of 210.15 g/mol.
• The mass of reactants needed in Part C is dependent on the pressure and temperature of the room. The plastic bag has an approximate volume of 0.560 L. For a room at approximately 24.0 °C and a pressure of 1 atm, the amount of moles of CO₂ gas produced can be calculated using the following information:

  PV = nRT
  (1 atm)(0.560 L) = n(0.08206 L•atm•mole^–1•K^–1)(24.0 + 273.15)
  0.560 atm•L = n(24.384 L•atm•mole^–1)
  n = 0.02297 moles of CO₂ gas
  3NaHCO₃ + H₃C₆H₅O₇ → 3H₂O + 3CO₂ + Na₃C₆H₅O₇

  For every three moles of CO₂ produced, 3 moles of sodium bicarbonate is needed:

  {14113_Hints_Equation_3}

Teacher Tips

• Another fun activity is the Exploring a Chemical Reaction in a Toy—Student Laboratory Kit, Flinn Catalog No. AP7048. It’s a great activity to do before this lab. Students identify the chemicals in the self-inflating toy through testing and acid–base chemistry. A video of this activity, Bomb Bag, is available at www.flinnsci.com as part of the Flinn Scientific “Best Practices for Teaching Chemistry” teacher resources videos.

Answers to Prelab Questions

1. Write out the chemical formulas for sodium bicarbonate and citric acid.

   NaHCO₃ and H₃C₆H₅O₇ (or H₃C₆H₅O₇•H₂O)

2. Write the balanced chemical reaction between sodium bicarbonate and citric acid.

   3NaHCO₃ + H₃C₆H₅O₇ → 3H₂O + 3CO₂ + Na₃C₆H₅O₇

3. What is the gas that inflates the balloon?

   Carbon dioxide gas (CO₂)

Sample Data

Part B. Analyzing a Self-Inflating Balloon

Answers to Questions

Part A. Observations with Instructor

1. Record observations of the teacher’s self-inflating balloon.

   The balloon became cold when activated. Fizzing could be heard inside the balloon.

2. Record observations of a self-inflating balloon made from a plastic bag.

   Make sure the edges of the plastic bag balloon are securely taped. Shake the balloon, do not squeeze the balloon.

3. Calculate the amount of baking soda needed to fill the self-inflating balloon full of carbon dioxide gas at room temperature and pressure. Show all work.

   3NaHCO₃(s) + H₃C₆H₅O₇(aq) → 3H₂O(l) + 3CO₂(g) + Na₃C₆H₅O₇(aq)
   PV = nRT
   (1 atm)(0.378 L) = n(0.08206 L•atm•mole^–1•K^–1)(23.7 + 273.15)
   0.378 atm•L = n(24.359511 L•atm•mole^–1)
   n = 0.01551755 moles CO₂

   {14113_Answers_Equation_4}

   In order to inflate the balloon to 378.0 mL, 1.30 g of sodium bicarbonate is needed.

4. Was the sodium bicarbonate provided in the balloon limiting or excess in this reaction? Support the answer with evidence.

   1.74 g of sodium bicarbonate was included in the balloon. However, only 1.30 g of sodium bicarbonate was necessary for the balloon to inflate. Therefore, the sodium bicarbonate was in excess and the citric acid was limiting. If there had been more citric acid, the balloon could have burst.

5. Given the volume of gas needed to inflate the self-inflating plastic bag balloon, calculate the mass of sodium bicarbonate and citric acid needed to inflate the bag. Show your calculations below.

   PV = nRT
   (1 atm)(0.560 L) = n(0.08206 L•atm•mole^–1•K^–1)(24.0 + 273.15)
   0.560 atm•L = n(24.384 L•atm•mole^–1)
   n = 0.02297moles of CO₂ gas
   3NaHCO₃(s) + H₃C₆H₅O₇(aq) → 3H₂O(l) + 3CO₂(g) + Na₃C₆H₅O₇(aq)
   For every three moles of CO₂ produced, 3 moles of sodium bicarbonate is needed:

   {14113_Answers_Equation_5}
6. Record observations of the plastic bag self-inflating balloon.

   The balloon became cold when the reaction occurred. Fizzing was heard and bubbles could be seen inside the clear plastic bag. The bag increased in volume.

7. To inflate a self-inflating balloon to a volume of 2.3 L at a room temperature of 25 °C, how much baking soda and citric acid would be needed?

   PV = nRT
   (1 atm)(2.3L) = n(0.08206 L•atm•mole^–1•K^–1)(25 + 273.15)
   2.3 atm•L = n(24.45388L•atm•mole^–1)
   n = 0.094 moles of CO₂ gas
   3NaHCO₃(s) + H₃C₆H₅O₇(aq) → 3H₂O(l) + 3CO₂(g) + Na₃C₆H₅O₇(aq)

   {14113_Answers_Equation_6}

References

Special thanks to Kathleen Dombrink, McCluer North High School, Florissant, MO, for sharing this activity with Flinn Scientific.

Introduction

Did you ever wonder how a self-inflating balloon works? Have fun investigating this novelty balloon with this activity! Apply stoichiometry and the ideal gas law to make your very own self-inflating balloon!

Concepts

• Stoichiometry
• Limiting and excess reactants
• Ideal gas law
• Acids and bases

Background

A self-inflating balloon is a sealed Mylar^® balloon that contains sodium bicarbonate, also known as baking soda (NaHCO₃) and a packet of “water.” The small packet of “water” is an aqueous solution of citric acid (H₃C₆H₅O₇(aq)). When the citric acid packet is broken, the chemicals react and inflate the balloon (Equation 1).

where

P = pressure (atm)
V = volume (L)
n = number of moles
R = universal gas constant
T = temperature (K)

Experiment Overview

The purpose of this experiment is to analyze the stoichiometry involved to determine the limiting reactant in a self-inflating balloon reaction. The data will be analyzed and applied in creating your own self-inflating balloon.

Materials

Prelab Questions

1. Write out the chemical formulas for sodium bicarbonate and citric acid.
2. Write the balanced chemical reaction between sodium bicarbonate and citric acid.
3. What is the gas that inflates the balloon?

Safety Precautions

Citric acid, sodium bicarbonate and the contents of the self-inflating balloon may be irritating to skin, and especially irritating to the eyes. Sodium bicarbonate may be harmful if swallowed. Avoid contact of all chemicals with eyes and skin and wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part A. Observations with Instructor

1. Observe the teacher inflating one of the self-inflating balloons.
2. Observe an example of a self-inflating balloon made from a plastic bag.
3. Write down your observations of both balloons on the Stoichiometry of the Self-Inflating Balloon Worksheet.

4. Obtain a balloon from the instructor. Carefully cut a small opening into the balloon. Note: It is important to keep the opening small. You will be determining the volume of the balloon and need to keep it as intact as possible.
5. Carefully remove the aqueous citric acid packet using forceps.
6. Measure the weight of an empty, clean weigh dish.
7. Carefully remove the sodium bicarbonate solid and collect it in a weighing dish.
8. Weigh the weigh dish with the sodium bicarbonate.
9. Record the mass of only the sodium bicarbonate solid in Data Table 1.
10. Using water, fill up the self-inflating balloon and then pour the water into a 600-mL beaker.
11. Using a graduated cylinder, measure the water from the balloon and record in Data Table 1.
12. Determine the temperature and pressure in the room according to the teacher’s instructions and record these values in Data Table 1.

13. Obtain a plastic bag. This will be your new self-inflating balloon.
14. Decorate the bag with permanent markers (see Figure 1, for ideas).
    {14113_Procedure_Figure_1}
15. Find the volume of the plastic bag in milliliters (see steps 10–11). Record the volume in Data Table 2.
16. Dry the plastic bag.
17. Record the temperature and pressure of the room in Data Table 2.
18. Use the ideal gas law to calculate the amount of sodium bicarbonate and citric acid needed to inflate your balloon. Show your work on the worksheet and record the masses in Data Table 2.
19. Measure the solid sodium bicarbonate and solid citric acid.
20. Place the two solids in the plastic bag.
21. Take a pipet and cut all but 2 cm of the stem (see Figure 2).
    {14113_Procedure_Figure_2}
22. Fill the pipet with water and carefully place it upright in the bag, so it does not spill.
23. Carefully seal the bag without releasing the water. Get as much air out of the bag as possible.
24. Transparent tape can be used around the edges to prevent leaking (see Figure 3).
    {14113_Procedure_Figure_3}
25. Shake the bag so the water mixes with the two solids and they react. DO NOT squeeze the bag.
26. Consult your instructor for appropriate disposal proceedures.

Student Worksheet PDF

14113_Student1.pdf