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Air Bag Stoichiometry (23 Favorites)

PROJECT in Gas Laws, Chemical Change. Last updated April 26, 2018.


Summary

In this lab, students make real-world connections of stoichiometry with the design of car air bag.

Grade Level

High school

Objectives

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

  • Understand that stoichiometry is used in real-life scenarios.
  • Carry out stoichiometry problems with solid, aqueous, and gaseous states.

Chemistry Topics

This lesson supports students’ understanding of

  • Stoichiometry
  • Ideal gas law

Time

Teacher Preparation: less than 10 minutes

Lesson: 1 hour for each part

Materials

PART 1

  • Computer with internet access

PART 2

  • 25-mL graduated cylinder
  • Balance
  • Weighing boats
  • 150 mL of 5% vinegar solution (acetic acid)
  • 10.5 g of baking soda (sodium bicarbonate)
  • 1-quart Ziploc bag
  • Timer

PART 3

  • An egg in a plastic bag
  • Two 1-quart Zip lock bags
  • 5% vinegar solution (acetic acid)
  • Baking soda (sodium bicarbonate)
  • Tape
  • Graduated cylinder
  • Balance
  • Weighing boat

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Use caution when handling acetic acid. If any acid comes into contact with skin, flush with water immediately.

Teacher Notes

  • Suggested grading scale (see Rubric document for suggest point break down):

Part 1: 10 points

Part 2: 40 points

Part 3: 40 points

  • The balanced equation in Part 2 is: NaHCO3 (s) + CH3COOH (aq) ⇾ CO2 (g) + NaCH3COO (aq) + H2O (l)
  • In Part 2, the bag should inflate to about 590 mL (at 72 oC and 1 atm), and 1 quart is 946.6 mL, so the bag should not fully inflate. To inflate the bag to 940 mL, students should use .033 mol of reactants (2.8 g NaHCO3 and 40 mL 5% vinegar).

For the Student

Lesson

PART 1

Prelab Questions
This project begins with an internet exploration of how car air bag works. Answer the following question. Here are some references you may use. At the end, indicate which of these references you used in addition to any other references.

  1. What is the intended purpose of an air bag?
  2. How does an air bag deploy? Describe the process.
  3. What is the chemistry behind an air bag? Write the balanced main chemical reaction and secondary reactions. Note: Not all air bags have the same secondary reaction.
  4. What gas fills the air bag? Why was this gas chosen to use in an air bag?
  5. What is the function of the secondary chemical reactions in an air bag?
  6. What is the approximate volume of an air bag when it is fully inflated?
  7. What happens if an air bag is under inflated? What would be the cause?
  8. What happens if an air bag is over inflated? What would be the cause?
  9. How long does it take for an air bag to inflate? Is this timing important? Explain.
  10. Do you want to have any chemicals left over in an air bag after it inflates? Explain.
  11. What five factors would you consider if you had to design a functional and safe air bag? Which factor do you think is most important? Explain.

References:

PART 2: The Air Bag Stoichiometry Project

Background

Create your own air bag technology using sodium bicarbonate and acetic acid.

Find the right amounts of sodium bicarbonate and acetic acid needed to fill the bag. “The right amount” means your bag, a 1-quart zip lock, should fill up and not pop open, and no sodium bicarbonate or acetic acid should be left in the bag.

Before starting, look at the data table. You will record the amounts of acetic acid and sodium bicarbonate, a description of how the bag inflated, what chemical was in excess, and the amount of time it took for the reaction to take place.

Hypothesis

Which bag do you predict will produce the greatest amount of CO2? Circle your prediction.

bag #1 - 25 mL of vinegar + 0.5 g of sodium bicarbonate

bag #2 - 25 mL of vinegar + 1.0 g of sodium bicarbonate

bag #3 - 25 mL of vinegar + 1.5 g of sodium bicarbonate

bag #4 - 25 mL of vinegar + 2.0 g of sodium bicarbonate

bag #5 - 25 mL of vinegar + 2.5 g of sodium bicarbonate

bag #6 - 25 mL of vinegar + 3.0 g of sodium bicarbonate

Procedure

  1. Mass 0.5 grams of sodium bicarbonate and record the exact mass in the data table. Carefully pour it from the weighing boat into a bag. Flatten the bag to remove any air.
  2. Add 25 mL of vinegar to the bag and seal the bag as quickly as possible. Start the timer. The bag should begin to inflate.
  3. When the bubbling stops, further mix the acetic acid and sodium bicarbonate by squishing and/or shaking the bag to make sure the reaction proceeds as far as possible. When no more bubbles are produced, stop the timer. Record how long it took for the chemicals to react.
  4. Test how inflated the bag is by pinching it. Write a description and rank the fullness of the bag in the data table. Also, does the bag feel warm or cold? Make a note of that.
  5. Record in the data table whether there is any sodium bicarbonate left in the bag.
  6. If all of the sodium bicarbonate seems to be gone, open the bag and add a small amount of sodium bicarbonate to see if more bubbles form. If they do, then there is still some acetic acid left in the bag. If not, then all of the acetic acid reacted. Record in the data table the excess reactant.
  7. Repeat this process by increasing the amount of sodium bicarbonate by 0.5 g until you use 3.0 g of sodium bicarbonate.

Data

Bag#

Acetic
acid

Sodium bicarbonate

Description of bag (warm/cold, other observations)

Fullness rank

Excess reactant

Time to fill the bag (sec)

1

25 mL

0.5 g

2

25 mL

1.0 g

3

25 mL

1.5 g

4

25 mL

2.0 g

5

25 mL

2.5 g

6

25 mL

3.0 g

Calculations

Assume the concentration of acetic acid is 5% and its density is 1 g/mL.

Bag#

Moles of acetic acid

Moles of NaHCO3

Moles of CO2 formed

Moles of NaHCO3
left

Moles of CH3COOH
left

Limiting reactant

Excess reactant

1

2

3

4

5

6

Analysis

  1. Write the balanced chemical equation between acetic acid and sodium bicarbonate. What is the mole ratio of acetic acid and sodium bicarbonate?
  2. Calculate how many grams of sodium bicarbonate are needed to completely react with 25 mL of vinegar (5% acetic acid).
  3. Which bags have less sodium bicarbonate than your calculation in question two? Did you observe any leftover sodium bicarbonate or vinegar in these bags?
  4. Which bag has the closest amount of sodium bicarbonate you calculated in question two? Did you observe any leftover of sodium bicarbonate or vinegar in that bag?
  5. Which bags have more sodium bicarbonate than your calculation in question two? Did you observe any leftover sodium bicarbonate or vinegar in these bags?
  6. Which bag is most inflated with no leftovers? Is this what you predicted in your hypotheses? How would you revise your hypotheses?
  7. How are your observations of fullness of the bag compared with how much CO2 formed according to the calculations?
  8. Did any bag fully inflate? If not, explain what you would do to fully inflate the bag. Can you propose a procedure to make a full bag?
  9. From your observations, how long does it take to fully inflate the bag?
  10. From your observations, can you determine whether this reaction is endothermic or exothermic? Explain.
  11. Why is this reaction a good candidate for the real car air bag? Why is this reaction not a good candidate for the real car air bag? Explain your answer. You can revisit Part 1.

Conclusion

Car air bag

Your air bag

Chemical reaction

Volume in Liters

Time to deploy

PART 3: The Crash Test

Now you will put what you found in part 2 to the test: a crash test. You will design and build a vehicle for your crash test dummy, which is a raw egg. The goal is to build a vehicle that will protect an egg from breaking, even when dropped from a height of three stories.

The only materials you can use are:

  • an egg in a plastic bag
  • two 1-quart zip lock bags
  • 100 mL 5% acetic acid
  • sodium bicarbonate
  • tape
  • a graduated cylinder
  • a balance

Your bags should fully inflate and not have any acetic acid or sodium bicarbonate left over.

Procedure

  1. Review the difference of car air bags and your air bag and the assessment rubric before you start your work.
  2. Complete your group planning steps one, two, and three. Show your work to your teacher.
  3. Once your procedure is approved, carry out the reaction and inflate both bags according to your procedure.
  4. Show your bags to your teacher for an examination of any leftover of reactants.
  5. Assemble the inflated bag(s) and the egg (in a plastic bag) together.
  6. Design your vehicle (step four) and get approval from your teacher.
  7. When it’s your turn, drop your vehicle.
  8. Check your passenger. Did it survive the crash? Show your vehicle to your teacher after the crash test.
  9. Complete and submit your worksheet.

Planning your work

  1. Look at the data from your experiment (part 2). How many grams of sodium bicarbonate and how many mL of acetic acid did you add without any excess after the reaction?
  2. Did this amount of sodium bicarbonate inflate the bag fully? If not, how could you change the amounts of the reactants so the bag is full but with no reactants left over? Assume 1.0 L of CO2 at STP will fully inflate a 1-quart bag.
  3. One a separate piece of paper, write a procedure for your air bag and show it to your teacher before you proceed.
  4. Remember, your air bag is going to protect an egg as it’s dropped from three stories. Design your vehicle and draw a picture of it.
  5. If your passenger did not survive the “crash test,” explain what you could do to improve your design. If your passenger did survive, explain why it did.
  6. What is another real-life example where stoichiometry is important?

Conclusion

From part 1, you know the following reaction occurs in a real air bag:

NaN3(s) ⇾ Na(s) + N2(g)

If 65.1 L at STP of N2 gas are needed to inflate a real air bag to the proper size, how many grams of NaN3 must be included in the real air bag to generate this amount of N2?