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Transcript of Airbag Lab
Questions are being raised as to whether airbags should be mandatory, and whether their safety can be improved. How much does the number of deaths or serious injuries decrease when an airbag and seat belt are used, as compared to when a seat belt is used alone? How many people are airbags killing or seriously injuring? Do the benefits of airbags outnumber the disadvantages? How can airbags be improved? Also, are airbags an environmental time bomb? What is being done to dispose of unused the poisonous sodium azide left in airbags?
The automobile air bag is a remarkable device. It is deceptively 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 non-toxic, odorless, and cool enough to avoid burning the occupants. You‟d also like the compounds used to be stable, and non-toxic, so they don‟t expand unexpectedly and are easy and safe to dispose of. Sensors detect impact and electrically initiate the following reaction to activate modern air bags: 2 NaN3 (s) --> 2 Na (s) + 3 N2 (g) Sodium azide (NaN3) is a stable solid and a small pellet can easily be stored in air bag compartments. The huge volume of nitrogen (N2) gas is produced rapidly and is non-toxic and relatively cool. Sodium azide itself, however, is pretty nasty. A biologist needs just a few micrograms per liter to prevent bacterial growth in biological preparations. Toxic chemicals like sodium azide are a major concern in landfills where undeployed air bags are discarded.
How Airbags Work!
Inside the airbag is a gas generator containing a mixture of NaN3, KNO3, and SiO2. When the car undergoes a head-on collision, a series of three chemical reactions inside the gas generator produce gas (N2) to fill the airbag and convert NaN3, which is highly toxic, to harmless glass. Sodium azide (NaN3) can decompose at 300oC to produce sodium metal (Na) and nitrogen gas (N2). The signal from the deceleration sensor ignites the gas-generator mixture by an electrical impulse, creating the high-temperature condition necessary for NaN3 to decompose. The nitrogen gas that is generated then fills the airbag. The purpose of the KNO3 and SiO2 is to remove the sodium metal (which is highly reactive and potentially explosive, by converting it to a harmless material. First, the sodium reacts with potassium nitrate (KNO3) to produce potassium oxide (K2O), sodium oxide (Na2O), and additional N2 gas. The N2 generated in this second reaction also fills the airbag, and the metal oxides react with silicon dioxide (SiO2) in a final reaction to produce silicate glass, which is harmless and stable.
Chemical Reactions Used to Generate Gas
Reaction 1:2NaN3 --> 2Na + 3N2
Reaction 2:10Na + 2KNO3 --> K2O + 5Na2O + N2
Reaction 3:K2O + Na2O + SiO2 --> Na2K2SiO4 (alkaline silicate glass)
1. Find the volume of a bag by filling it with water and pouring it into a graduated cylinder (This is volume of CO2).
2. Use the Ideal gas law to determine the amount of moles of CO2 that can fill the bag (Pressure = 1atm)
3. Use a stoichiometry conversion to convert from moles of CO2 to grams of NaHCO3
4. Use a stoichiometry conversion to convert grams of NaHCO3 to moles of HC2H3O2 (vinegar) need for the reaction
5. Use the concept of Molarity (mol/L) to determine the volume of HC2H3O2 solution needed in step #4.
P = 1 atm
T = 24 celsius
Make a ruled and neatly organized/easy to read data table(s) that includes all measurements made in this lab experiment and summarizes your major findings. Use units and significant figures!
Data for the determination of the volume of the plastic bag
Mass sodium bicarbonate used
Volume 0.8 M acetic acid used
Total mass of bag and reactants
Theoretical volume of CO2 produced
Height of the bag after the reaction
Time needed for the maximal inflation of the bag
Moles of each reactant added
Analysis of the Results
Label all calculations and clearly show work using dimensional analysis, units and sig. figs.
1. Calculate the volume of the Zip-lock Bag
2. Calculate the minimum amount of each reactant needed to fill the bag.
3. Address the following questions for your best airbag.
a.) For your best airbag, which reactant was in excess? Which reactant was your limiting reactant? Explain how and why this contributed to it being your best airbag.
b.) Calculate theoretical volume of CO2 produced in your best "airbag?"
c.) What was the approximate (estimated) volume of CO2 produced in your best "airbag?"
d.) What was the percent yield for the production of carbon dioxide in your best airbag?
e.) What were the major sources of error that account for the % yield of your best airbag not being 100%.
Conclusion Use bullets to summarize your major findings and the major sources of error.
Table of Contents
Date Lecture/Activity Pg#
81 04/13/15 Airbag Lab 137
I will use gas stoichiometry to calculate the correct
amount of reactants required to inflate a ziplock
bag to its' maximum capacity.
Describe how you think an airbag in your vechile
C2H4O2 + NaHCO3 --> NaC2H3O2 + H2O + CO2