Pre-Lab: Name: ______________________
- This lab requires chemistry calculation work and an engineering process. Collaborate with members of your group to come up with some engineering and computational ideas that will give you the edge in the class competition. Read the lab to define your equipment and parameters. Quiz on the following via BB before lab. It may be instructive to run through mock calculations before lab.
- Consider that a typical driver-side airbag contains 50.0 g of sodium azide, what volume of nitrogen gas would be produced upon ignition assuming sodium azide is the limiting reagent? You may assume a temperature of 25ºC and an atmospheric pressure of 760 mmHg for your prelab calculation.
- You are in competition with other groups, so are encouraged to not share information.
Your lab work this semester has spanned topics as diverse as calorimetry and stoichiometry. This lab will require you to synthesize many of the practical and computational skills that you have acquired during your lab tenure. You will generate your own procedure and data collection and will work in competition with the other lab groups in your section. You will submit this lab as a handwritten lab report today and will write your second formal report on your lab findings for submission as a signature project at a future date. In addition to your handwritten report, your airbag, calculations, and engineering will be judged in class. Some of the questions that will be asked in an interview are:
- How did you determine the volume of the bag?
- What volume of acetic acid did you choose?
- What mass of baking soda did you choose?
- What was the limiting reagent?
- Did you perform a “test” experiment first?
- Did your reaction go to completion? How do you know?
- Is your reaction endothermic or exothermic? How does this affect the usefulness of this application of your reaction?
The chemistry process and calculations that you use in creation of an airbag supersede the performance of the airbag itself.
How does an Airbag Work?
An automobile airbag must both inflate quickly and produce inert, non-flammable products to be both safe and useful. Modern air bags accomplish both through a sodium azide (NaN3(s)) reaction, which inflates an airbag in less than 0.3 seconds. An open bag design ‘softens’ the large airbag, which is designed to both reduce acceleration and distribute force over a greater area than a steering wheel or car interior, reducing injuries. The chemistry involved is both elegant and precise. Stoichiometric masses of reactants must be used to ensure a complete reaction toward the inert nitrogen gas and silicon dioxide (glass) products according to the following reactions. The first of which is the electrical ignition of the sodium azide explosive when a sensor communicates a collision.
2NaN3(s) à 2Na(s) + 3N2(g) Reaction 1
The highly reactive sodium metal produced in reaction one is further reacted with solid potassium nitrate in a second reaction to produce a less reactive oxide and still more nitrogen gas.
10 Na(s) + 2 KNO3(s) à K2O(s) + 5 Na2O(s) + N2(g) Reaction 2
Reactions one and two can be summed to the following reaction.
10 NaN3(s) + 2 KNO3(s) à 5 Na2O(s) + K2O(s) + 16 N2(g) Reaction 3
The solid products are then combined with solid silicon dioxide in a fourth reaction to produce a safe and inflammable product, glass.
K2O(s) + Na2O(s) + SiO2(s) à glass Reaction 4
Some elements of the sodium azide detonation can be reproduced in lab. Using an explosive in a lab setting that allows for trials is unsafe. You can, however, safely produce an inert gas in a more controlled (slow) manner. Like the sodium azide detonation, you should consider that all the products of your reaction will be present after a collision.
- Using provided chemistry concepts learned through the semester, design, calculate, and build a simulation of an automobile airbag.
- Design your own procedure and data collection and calculation.
- Wear splash goggles at all times. You are creating pressure, and the bag may open.
- 6 M acetic acid is toxic by ingestion and inhalation and corrosive to skin and eyes; avoid contact with bodily tissues. *The acetic acid used is more concentrated than household vinegar.
- Dispose of spent airbag liquid waste by dumping the contents of your bag into the waste container located in hood one then disposing your bag into the regular trash.
- Clean your bench top and any acid spills with baking soda solution.
- Two (2) quart Ziplock® bags
- Baking soda (sodium bicarbonate, NaHCO3(s)
- 6 M acetic acid (HC2H3O2)
- Any glassware from drawer (within reason and as approved for safety by your instructor)
- Classroom consumables
- Analytical Balance
- Barometer: Pressure sensor
- Alcohol thermometer
- List any chemical reactions used in your airbag design.
- Calculations: Include any necessary calculations in a logical and readable format.
- When ready, demonstrate the collision and reaction of your airbag components to your instructor and answer the interview questions.
- Turn this lab in at the end of class today for a lab grade in conjunction with the class competition and interview.
- Keep your lab notebook with all notes and calculations for use in your second formal lab report, due in one week. Your formal report is your signature project and will be uploaded to your BB shell under assignments.
You will use the data and observations from this lab to complete your second formal lab report. Please see the Formal Lab Documents tab included in your BB shell, including the requirements found document, How to Write a Formal Lab Report found in your Formal Lab Documents file. To help you reference the file, this incomplete list may help.
- A journal sourced application of the lab technique to be included in your Introduction
- Any assumptions made in your Introduction
- Any formulas or reactions used in your Introduction
- Develop a clear problem statement in your Introduction, identifying the information necessary to solve the problem
- Evaluate at least two possible methods that you can use to solve the problem and defend the method you have chosen. For example, you may use two different gas laws to calculate the volumes and masses to fill your airbag and evaluate which is appropriate for the experimental conditions
- An Experimental section (bullets, numbered, or paragraph) providing a reproducible procedure, including the actual masses and concentrations that you used
- Tabulated raw data in your Results and Discussion
- Sample calculations in your Results and Discussion
- Discussion of any differences in theoretical and actual volumes of gas produced
- Findings should be listed in the Abstract, Results and Discussion, and Conclusion and discussed in the Results and Discussion section
- Address whether the assumptions listed in the introduction were validated or invalidated in the Conclusion section
- Reflect on your results in your Conclusion, for example, was your method the appropriate for the conditions that you tested
- Reference citations (not URL) after the Conclusion
- An originality report will be automatically generated upon your submission of the exam and will be visible to you. Please note that in science writing, direct quotations aren’t used. You must, therefore, convey the ideas and theories as well as past work cited by literature without plagiarizing another’s work. The originality report will alert me to similar reports across sections and semesters. It is reasonable to report the same measurements and numerical data as your lab partner. Duplicated work of less than 15% is generally accepted in journal writing. Unoriginal content of greater than 25% is generally considered plagiarized in journal writing. Reproduced writing, except as described previously, whether from a literature source or another student represents plagiarism, and the first instance will result in a zero grade for the assignment without the opportunity to re-write the assignment.
Adapted From Dieckmann, G., Sibert, J. In An Atoms First Approach to the General Chemistry Laboratory; McGraw Hill: New York, NY, 2014; pp 159–164.