Introduction / Background
College students all lead busy lives, but few students take advantage of the convenience of pressure cookers, much less understand how they work. This case study uses a daily cooking scenario to demonstrate how the boiling point of water is directly related to the external pressures in order to reinforce the concepts of boiling and boiling point, apply ideal gas law, and relate chemical reaction rates with temperatures. It also extends its teaching to autoclaves used to destroy microorganisms and toxins in the medical field and promotes awareness of time and energy conservations, benefiting students as well as the environment.
This case study can be used as a supplement for the Gas Law chapter in non-major general chemistry courses such as General Chemistry, Fundamentals of Chemistry, General, Organic and Biological Chemistry I as well as Nutrition. It is also an informal writing assignment for any of these courses that are also designated as writing intensive.
Objectives
- Stimulate students’ interest in chemistry.
- Reinforce chemistry concepts and scientific thinking skills.
- Enhance the concept of vapor pressure of water.
- Emphasize that the boiling points of water vary with external pressures.
- Demonstrate that chemical reaction rates increase at higher temperatures.
- Apply the ideal gas law to explain a real life scenario.
- Practice unit conversion skills.
- Create awareness of energy conservation in daily life.
Classroom Management
| Pressure (mmHg) | Boiling Point (°C) |
|---|---|
| 270 | 70 |
| 467 | 87 |
| 630 | 93 |
| 752 | 99 |
| 760 (1 atm) | 100 |
| 800 | 100.4 |
| 1075 | 110 |
| 1520 (2 atm) | 120 |
| 2026 | 130 |
| 7600 (10 atm) | 180 |
A copy of the case and the data of boiling point of water under different pressures (Timberlake, see Table 1) should be provided at the beginning of gas law lectures.
After about one week, students can use one hour of lab time to examine the data and discuss the case among themselves in study groups (two to three people) and complete the questions associated with the case.
The discussion should be in the following areas: (1) What is boiling and boiling point? (2) What is vapor pressure of water? (3) What is external pressure? (4) How does the boiling point of water relate to external pressures and why? (5) How does a pressure cooker speed up the cooking process? (6) Why does a slow cooker cook food slowly? (7) Apply the ideal gas law to explain why a pressure cooker explodes when its vent is blocked.
Subsequently students can share their personal experience with pressure cooking, if any, within each study group.
Answer Key
Answers to the questions posed in the case study are provided in a separate answer key to the case. Those answers are password-protected. To access the answers for this case, go to the key. You will be prompted for a username and password. If you have not yet registered with us, you can see whether you are eligible for an account by reviewing our password policy and then apply online or write to answerkey@sciencecases.org.
References
Print Sources
- Boehm, H. Steam pressure cooking pot with a seal securing the inside space of the pot against a drop in pressure. United States Patent, Patent Number 4,733,795, March 29, 1988.
- Norton, A.J., S. Jordan, and P. Yeomans. 1994. Brief, high-temperature heat denaturation (pressure cooking): A simple and effective method of antigen retrieval for routinely processed tissues. The Journal of Pathology 173(4): 371–379. (Available online at: http://www3.interscience.wiley.com/journal/110535719/abstract)
- Timberlake, K. 2002. General, Organic, and Biological Chemistry: Structures of Life. San Francisco: Benjamin Cummings.
Websites
- Pressure Cooker Primer by Cheri Sicard, July 29, 2007, FabulousFoods.com
- http://www.fabulousfoods.com/school/cstools/pressurecooker/pressurecooker.html#what Last accessed: May 15, 2009
- The Benefits of Using a Pressure Cooker
- http://missvickie.com/library/benefits.html Last accessed: may 15, 2009
- Why are nutrients preserved in a pressure cooker? Yahoo!Answers
- http://answers.yahoo.com/question/index?qid=20080207155757AAimZIP Last accessed: May 15, 2009
Acknowledgements: This case was published with support from the National Science Foundation under CCLI Award #0341279. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Date Posted: June 19, 2009.
Originally published at http://www.sciencecases.org/pressure_cooking/notes.asp
Copyright © 1999–2010 by the National Center for Case Study Teaching in Science. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.
