Purpose: To design and construct a model “airbag” using sodium bicarbonate, acetic acid, and a snack-size Ziploc bag
Introduction: The development of the air bag for automobiles required the combined efforts of both chemists and
engineers. The basic idea is simple: in the event of a collision, a plastic bag rapidly inflates with a gas, preventing the
occupant from hitting the dashboard or the steering column. The bag must:
1.
2.
3.
4.
5.
Not inflate by accident
Produce non-toxic materials
Produce a gas that is cool
Inflate very rapidly (20-60 milliseconds)
Be lightweight, easy to handle, and stable for long periods
The chemical reaction that occurs in most air bag systems is the decomposition of sodium azide (Na3N), producing
nitrogen, an extremely unreactive gas. The reaction is as follows:
2Na3N(s) → 6Na(s) + N2(g)
Sensors that detect an impact activate the air bag system. The sensor sends a current along a detonator, which causes a
small explosion to start the decomposition of sodium azide. A few milliseconds later, about 60 liters of nitrogen gas
inflate the bag.
The sodium produced is very reactive and must be converted to a less hazardous material. The most common method
involves the reaction with Iron (III) oxide otherwise known as rust
Fe2O3(s) + 6Na(s) → 3Na2O(s) + 2Fe(s)
Since sodium azide is extremely toxic (it is a carcinogen as well as a skin and eye irritant) you will use another gas
producing reaction to construct your airbag: the reaction between sodium bicarbonate (NaHCO3) and acetic acid
(CH3COOH) to form carbon dioxide gas. The reaction is written as follows
Sodium bicarbonate + acetic acid → sodium acetate + carbon dioxide + water
NaHCO3(s) + CH3COOH(aq) → NaCH3CO2(aq) + CO2(g) + H2O(l)
Materials
Snack size Ziploc bag
10 mL graduated cylinder
100 mL graduated cylinder
6M acetic acid
Sodium bicarbonate
Safety goggles
Scoopula or plastic spoon
Electronic Balance
Safety
Electronic balance
Wear safety goggles at all times
Do not ingest any of the chemicals
Acetic acid is an irritant, so avoid direct
exposure to skin
Wash your hands thoroughly at the end
of the lab
Thornburg 2014
Your Task:
The objective is to inflate the snack-size Ziploc bag provided with the carbon dioxide produced in the reaction. When
inflated, the bag should be firm, but should not burst. You should optimize your system to inflate as rapidly as possible.
You will use an indirect method of finding the maximum amount of volume that can be held by your snack-size Ziploc
bag. It turns out that the volume of water our snack-sized Ziploc bag will contain when zipped closed is equal to the
maximum volume of CO2 (gas) that you wish to produce.
Procedure:
1. Determine maximum amount of volume for your Ziploc bag. (each bag is unique)
a. Fill your bag with water
b. Pour your water in a graduated cylinder to find the volume of the bag. The volume of water is the same
as the volume of CO2
2. Perform calculations to determine amount needed for NaHCO3 and CH3COOH
i. Calculation
1. Given: volume of CO2
(this was the volume of water your Ziploc bag contained when zipped closed)
Remember to convert milliliters (mL) into liters (L), 1000mL = 1L (take your answer in
mL and divide by 1000)
Want: grams of NaHCO3
ii. Calculation
1. Given: grams of NaHCO3 (what you just calculated above)
Want: volume of CH3COOH
***NOTE: you must take the final volume of CH3COOH calculated and divide it by 6.
(This is due to the fact that the solution is 6M concentration, which you will learn about
in the next couple of weeks.)
***NOTE: you must convert your answer in Liters (L) into milliliters (mL) because the
graduated cylinder measures quantities in mL not L. 1L = 1000mL (take your answer in L and
multiply by 1000)
3. Have your teacher check your calculations BEFORE proceeding with the experiment
4. Measure quantities of NaHCO3 and CH3COOH and record observations about the reactants
a. Use the balance to measure the correct mass of NaHCO3
b. Use the graduated cylinders to measure the correct volume of CH3COOH
5. Add reactants to the Ziploc bag
6. Quickly seal the bag and shake it around until the reactions stop
7. Record your observations. You will have one opportunity to inflate your air bag for 10 points. If your bag fails to
inflate (or bursts), you will have an opportunity to correct your procedure and inflate it a second time for 7
points.
8. When you have finished, pour the reactants down the drain and throw away the used zip lock bag.
Thornburg 2014
Name: _______________________________________________________
Period: __________
Sodium bicarbonate + acetic acid → sodium acetate + carbon dioxide + water
NaHCO3(s) + CH3COOH(aq) → NaCH3CO2(aq) + CO2(g) + H2O(l)
Volume of H2O
Volume of CO2
Calculation for grams of NaHCO3
Grams of NaHCO3
Calculation for volume of CH3COOH
Volume of CH3COOH
Observations for reactants
Observations of products (include at least… smell, color, temperature)
Sources of error. Explain in detail why your experiment was a success or failure and what you would do
differently next time.
Thornburg 2014
Sodium bicarbonate + acetic acid → sodium acetate + carbon dioxide + water
NaHCO3(s) + CH3COOH(aq) → NaCH3CO2(aq) + CO2(g) + H2O(l)
Volume of H2O
Volume of CO2
Calculation for grams of NaHCO3
Grams of NaHCO3
Calculation for volume of CH3COOH
Volume of CH3COOH
Observations for reactants
Observations of products (include at least… smell, color, temperature)
Sources of error. Explain in detail why your experiment was a success or failure and what you would do
differently next time.
Thornburg 2014