GAS LAW STOICHIOMETRY
Air Bag Background Information
Chemists can use concepts like stoichiometry, molar mass, and balanced chemical equations to predict just
about anything about a chemical reaction. The invention of the automobile air bag, for instance required
consideration of not only the chemistry, but economic and environmental factors. The automobile air bag is a
remarkable device. It is simple in concept, but the design requirements of the system are actually very
demanding. When a crash occurs, an air bag must inflate rapidly (within about 40 milliseconds), cushioning
the occupants against impact. The gas produced must be nontoxic, odorless, and cool enough to avoid
burning the occupants. You’d also like the compounds used to be stable, and nontoxic; so they don’t expand
unexpectedly and are easy and safe to dispose of and don’t create hazards in a land fill or junk yard.
Sodium azide (NaN3) is a stable solid and a small pellet can easily be stored in air bag compartments. A huge
volume of nitrogen (N2) gas is produced rapidly and is nontoxic and relatively cool. Sodium azide itself,
however, is pretty nasty. Toxic chemicals like sodium azide are a major concern in landfills where undeployed
air bags are discarded. These issues, as well as the quest for better and cheaper systems, keeps open the search
for other compounds and formulations for the gas-producing reaction used in the system.
Scenario objective: In this experiment, you have been asked by your boss, Iam Gaseous, of the AIR BAGS R
US Co. to investigate the design of a small-scale airbag system as a child safety device to put in baby carriages.
Your model airbag should expand to the largest possible volume without breaking the seal on the bag. To
simulate the airbag we will use a zip lock bag. To simulate the human head we will drop an egg onto the airbags
you create to check their efficiency. Because of sodium azide’s toxicity, Mr. Gaseous suggests you use look into
other reactions to test your engineering design.
Standard Temperature and Pressure
It was defined by the IUPAC as conditions at 273.15 K and 1 atm. Standard volume for a mole of gas at STP
conditions is 22.4 L. This means for any ideal gas at 273.15 K and 1 atm of pressure, a single mole will fill a
volume of 22.4 liters. This is a useful conversion for gas production and volume determination.
*Technically we are not at standard temperature, but the error is less than 5% so we will assume STP
The Mole
The mole is a quantity of measurement used by chemists for amounts of chemicals in a reaction. A mole now
has 4 conversion factors you should know.
1 mol = molar mass of the chemical
1 mole = avagadro’s number of particles
1 mol of gas = 22.4 L of gas at STP
Molar Ratio from balanced chemical equations
Stoichiometry is the study of chemical quantities. We use stoichiometry to investigate the relative amounts of
reactants and products. When investigating these relationships, don’t forget the golden rule of stoichiometry- all
quantitative relationships in chemistry are based on the mole! When comparing amounts of reactants and
products, we don’t talk about grams, liters, or molecules… we always compare molar amounts.
Based on experiments developed by Jim Klent and Angelica Stacy (ChemConnections)
PART ONE: AIRBAG INFLATION: Design an experiment to keep a baby egg from falling to its’ death.
Pre-Lab:
Assign the roles as follows below.
Dummy Provider- provideds crash test dummys- bring 2 eggs next class ____________________________________
Crash Test Initiator- responsible for initiating the crash and inflating airbag. ________________________________
Emergency Response Team- will tend to crash test dummy and clean up.
__________________________________________
1.
Obtain an “airbag”. This is your only airbag for the lab so don’t poke holes or break it! What things do you
need to determine regarding the bag? How might you figure those things out?
2.
Use your ideas above to determine physical properties of the bag. List them below with your measurements
including units!
3.
Why can we not use sodium azide for our reaction to fill the bag?
4.
You will need to research the Material and Safety Data Sheets (MSDS) for each chemical in this project.
For this lab we will start our trial run with acetic acid (HC2H3O2) and sodium bicarbonate.List the harzards
associated with each (google MSDS acetic acid and MSDS sodium bicarbonate and look at section 3)
5.
Write the balanced chemical equation for acetic acid and sodium bicarbonate. (Hint: H2CO3 will rapidly
break down into H2O and CO2 as products)
6. What product of the reaction will fill the bag up? ____________________________.
Lab Calculations:
7. How many liters of gaseous product should you produce to fill the bag? _________________________
Remember we want just enough gas to create a cushion without breaking the seal on the bag.
8. Determine how many grams of sodium bicarbonate you need to react to produce the volume of gaseous
product in #7. Assume we’re at STP.
9.
We want all of the sodium bicarbonate to react. Use your mass determined in #8 to calculate how many
grams of acetic acid you need to react.
10. The density of acetic acid is 1.05 grams in 1 mL (1.05g/mL). Determine the volume of acetic acid.
11. We will be using vinegar as our acetic acid source. Vinegar contains 5% acetic acid. How much vinegar
should you use? (Hint: Answer from #10 is only 5% of the total volume you need)
12. Before proceding to lab have your teacher grade you pre-lab work. Teacher approval ________________
Lab Build: It’s time to create your airbag! You will have a bag, vinegar, NaHCO3, scale, graduated cylinder.
13. In order to have the bag inflate properly, much like car airbags, the chemical reaction can only be activated
when triggered. Brainstorm ideas below to keep the reaction from occuring until you are ready for the bag to
inflate.
14. Pick your best idea above. You will have 1 trail run to fill your airbag. Take notes of what does and does not
work so you can make adjustments.
Crash Test Trails: You get 2 crash test dummy trials, but may not alter the air produced in the bag between trails.
Trail
Observations
Things to correct/adjust
Results
1
2
Post Lab Questions: Applying Gas Stoichiometry
15. Based on your lab data, if 2.01 g of NaHCO3 is used with excess vinegar will you produce too much, just
enough, or too little gas to fill the sandwich bag with gas. Justify your answer with calculations.
16. Write the balanced chemical reaction for an alternate reaction of hydrochloric acid and magnesium metal.
17.
Use the volume of the bag to calculate the mL of 6.0M HCl needed to fill the bag.