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by
Melinda Box
Department of Natural Sciences
Wake Technical Community College, Raleigh, NC
This case was used in a one-semester “Introduction to General, Organic, and Biochemistry” course offered as part of a two-year dental hygiene curriculum. It was incorporated into the course following the introduction of concepts related to gas behavior such as Boyle’s Law, Dalton’s Law, Charles’ Law, and the Combined Gas Law. Students may familiarize themselves with the Ideal Gas Equation through advance reading in order to respond to the case study dilemma.
The following topics are explored in class to help connect the information presented in the case to information on gas behavior previously discussed in class:
The reason for exploring the purpose of the parts of a regulator is that students then have the means to answer how they would verify gas cylinder specifications on a delivered tank.
To introduce the case study, students are first provided the case scenario to read. They are required to work in pairs or groups of three (assigned if necessary) and to brainstorm questions they may have about the situation after reading about it. They are encouraged to write down any questions, including things they could easily look up. During this time, the instructor circulates among the groups. As s/he learns what the students’ questions are, s/he writes them up on the board. Resources for addressing these questions and their answers are incorporated in the following discussion, below.
Likely student questions include: “How are gases in cylinders identified?” and “What is a coupling?”
In response to the second question, students are given Handout I, “Gas Cylinder Regulator Fittings.” The handout discusses the way that tank connectors vary with the gas in the cylinder connected. Although the word “coupling” is not used, students may deduce that a coupling refers to the threaded connection between a tank and a gas line based on the warning about unsafely “making” a regulator fit a tank. (A summary of a widely reported fatal accident that was caused by overriding this safeguard is included as part of the handout.) To test their comprehension of that, students are given Handout II, which depicts two gas regulators, and asked in their pairs to come to agreement about which part in the labeled illustration is the “coupling.” Although this illustration is labeled, it does not use the word “coupling.”
Using Handout II, students work in pairs to guess what each part of the regulator does. If students are collectively stuck, they can be reminded of what “pressure” is, i.e. force per unit area. In other words, the gas pushes on the cylinder and the gas is pushing on the air as it is flowing out. Both pressures are monitored. Only one is controlled.
The instructor ties the gas regulator illustrations to the case study by distributing Handout III, which contains a table with information on gas cylinder specifications. Handout III also includes illustrations of relative gas cylinder sizes. Students working in pairs must figure out how to verify that a delivered tank meets each of these specifications. In this process students should recognize that each gas has two volume values listed. The concept of gas storage conditions versus standard temperature and pressure conditions can be incorporated in explaining why two volume values are listed and what each means.
Students are asked to follow up the classroom discussion by responding in writing to the following questions:
Students are also provided with the grading guidelines. They must explain how gas cylinders are identified, state what forms of proof one might use to distinguish between each of the medical gases listed in the handout, and show calculations to support their method(s) of proof where applicable.
To aid them in their problem-solving, students may be told that they may assume a scale is available to weigh the tanks and that they either know or can find the mass of an empty tank or perhaps can compare the mass of the questionable tank to another full tank of less ambiguous identity.
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.
Acknowledgements: This case was developed 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: 10/25/06 nas
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Originally published at http://www.sciencecases.org/gas_cylinders/gas_cylinders_notes.asp
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