Group # _____ Name____________________ Stoichiometry Air Bag Lab Introduction: The airbag is now a common piece of safety equipment found in all new automobiles. Its development required the combined efforts of engineers and chemists. The concept is very simple; during a crash an impact is detected which sets off a controlled explosion and fills a bag in front of the carÕs occupants with gas. The reaction that occurs completely fills a plastic bag in front of the driver or passenger preventing possible head injuries. When designing a suitable reaction for an airbag several factors are taken into consideration. The reaction needs to be initiated quickly and easily, the reaction needs to come to completion quickly to ensure that the bag is filled before the driverÕs head strikes the steering wheel, and the gas produced should be inert and non-toxic to prevent possible explosion or poisoning. It is also necessary to use the right amount of chemicals (reactants) to completely fill the bag but not burst it. This last condition is an application of stoichiometry that we will investigate today. Real airbags utilize the decomposition of sodium azide (NaN3). Sodium azide decomposes explosively when an electrical current is passed through it to produce nitrogen, a chemically inert gas. Airbags have enough sodium azide to produce approximately 60L of gas in about 30 milliseconds. 2NaN3(s)  2Na(s) + 3N2(g) In this experiment we will avoid the use of explosive reactions and concentrate on a slower gas producing reaction. The purpose of the experiment is to calculate the amount of reactants needed to fill but not burst a plastic bag. You will test your calculated values in the laboratory and refine as necessary. In order to complete this experiment it is necessary to remember that one mole of any gas occupies approximately 22.4 L at STP. Objective: Create a small-scale air bag out of a zipper baggie using the reaction between baking soda and vinegar to create the CO2 gas needed to inflate the airbag. The finished air bag must have a mass that does not exceed 12.00 grams. You will be given limited raw materials with which to complete the task and ultimately you must maximize the volume of the bag. Pre-lab discussion: 1. How is our lab experiment similar to a real airbagÕs reaction and how is it different? 2. Summarize the objective of the lab. Background: You will use stoichiometric quantities of baking soda and vinegar to maximize the amount of CO2 gas created and minimize added mass due to unreacted vinegar or baking soda. Vinegar is only a 5% Acetic Acid solution and has a density of 1.01g/mL. Every mL you use will add 1.01 gram of mass. Since vinegar is only a 5% solution you need to multiply your mass by 5% (0.05) to calculate the actual amount of Acetic Acid being used. The balanced chemical equation for the reaction between baking soda and vinegar is: NaHCO3 + HC2H3O2  NaCH3COO + CO2 + H2O Baking soda + vinegar (acetic acid)  sodium acetate + carbon dioxide + water Materials: Each group will be given: 3 Baggies 2 pipettes 5 grams of baking soda 30 mL of vinegar 1 gram balance 10 mL graduated cylinder 1 weighing boat Group # _____ Name____________________ Problem: Each group must work efficiently and effectively to produce the most L of CO2 without going over 12.00 grams. Procedures/Data: 1. Label the zipper bags 1, 2, and 3 to represent each trial. 2. Record the mass of the zipper bag; mass of baking soda; volume of vinegar; and mass of zipper bag, baking soda, and vinegar combined for trial #1 in the table provided below. Make any notes that might be important for answering the questions later. One group member will use their fingers to separate the baggie into two sides and place vinegar into one side and baking soda into the other. Another group member will close the zipper, removing as much air as possible. Once the bag is closed, mix. 3. Complete all calculations for trial #1 and FIND YOUR TEACHER TO HAVE YOUR WORK CHECKED before attempting trial #2 so you know what adjustments must be made. 4. DO NOT DISCARD AIRBAGS UNTIL YOUR BEST AIRBAG IS CHECKED BY THE TEACHER. Trial # Mass of empty Zipper Bag Mass of NaHCO3 (baking soda) Volume of HC2H3O2 (vinegar) Mass of Bag + NaHCO3+ HC2H3O2 + + = + + = + + = 1 2 3 Calculations: 1. Trial # 1 ________g NaHCO3 x _____________ x ____________ x ____________ = L CO2 ________ml HC2H3O2 x 1.01= ___________ x 0.05 = __________ g HC2H3O2 __________ g HC2H3O2 x _____________ x ____________ x ____________ = L CO2 2. Trial # 2 ________g NaHCO3 x _____________ x ____________ x ____________ = L CO2 ________ml HC2H3O2 x 1.01= ___________ x 0.05 = __________ g HC2H3O2 __________ g HC2H3O2 x _____________ x ____________ x ____________ = L CO2 Group # _____ Name____________________ Trial # 3 ________g NaHCO3 x _____________ x _____________ x ______________ = L CO2 ________ml HC2H3O2 x 1.01= ___________ x 0.05 = __________ g HC2H3O2 _________ g HC2H3O2 x _____________ x _____________ x ____________ = L CO2 Teacher check: After all 3 trials are complete, call your teacher over to weigh your airbag. Analysis: 1. Review - What is a limiting reactant? 2. How can you tell which reactant in this experiment is the limiting reactant? 3. Identify the limiting reactant, if any, for each of the 3 trials (if neither reactant is the limiting reactant, write neither in the blank). Explain how you know it is the limiting reactant. Trial 1 - _____________________ is the limiting reactant becauseÉ Trial 2 - _____________________ is the limiting reactant becauseÉ Trial 3 - _____________________ is the limiting reactant becauseÉ Conclusion: Use Collins writing type II to write a conclusion about what you found was the best combination of baking soda and vinegar. Explain how you used your experimentation and calculations to adjust the amount of reactants in order to maximize the amount of carbon dioxide produced while limiting the mass of reactants to 12 grams. Also include a description of any challenges you had to overcome. X X X Group # _____ Name____________________ X X X X X X Self-Assessment and Follow-up Assignment On a scale of 1 to 3, rate your understanding of how to convert between grams and liters by using the following descriptors and circling your choice: 1 Ð I am struggling with understanding how to convert between grams and liters and need additional guided practice. Download the document ÒGuided Practice: Stoichiometry with LitersÓ. 2 Ð I think I understand how to convert between grams and liters but would like to make sure with additional individual practice. Download the document ÒAdditional Practice: Stoichiometry with LitersÓ. 3 Ð I completely understand how to convert between grams and liters and am ready to attempt more challenging applications of stoichiometry. Download the document ÒStoichiometry ChallengeÓ.