There is a Lot of Pressure, Partially, Involved

“Gases are distinguished from other forms of matter, not only by their power of indefinite expansion so as to fill any vessel, however large, and by the great effect heat has in dilating them, but by the uniformity and simplicity of the laws which regulate these changes.”
James Clerk Maxwell

When learning chemistry gasses get a lot of attention. There are a lot of laws and formulas that relate to gasses. Here is a list of gas laws:

1) Avogadro’s Law
2) Boyle’s Law
3) Charles’s Law
4) Gay-Lussac’s Law
5) The Ideal Gas Law
6) Dalton’s Law of Partial Pressures
7) van der Waals Equation (Non-Ideal gases)

I want to talk about Dalton’s Law of Partial Pressures. If you look up Dalton’s law like most students would Wikipedia via Google we see that the definition of Dalton’s law is: “Dalton’s law (also called Dalton’s law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.” Which comes from Silberberg, Martin S. (2009). Chemistry: the molecular nature of matter and change (5th ed.). Boston: McGraw-Hill. p. 206. ISBN 9780073048598.

I have not thought about Dalton’s law in years. The last time was when I was helping develop some chemistry labs. Then two weeks ago I ran across a YouTube video from Cody’sLab called Demonstrating The Law of Partial Pressures.

What I found interesting about this video is that Cody built a physical device to demonstrate the law. The device is two pressure chambers made out of copper plumbing parts and glass tubs attached with a simple valve. A quick search online suggests that one of these devices could cost less than $100.00. He uses the device to demonstrate several principles of Dalton’s Law. What I find fascinating about the device is that in many ways this device did a better job demonstrating Dalton’s law then any device I encounter in my high school or early chemistry classes.

With a small amount of work, it should be possible to build a device that was composed entirely of parts that could be screwed together allowing assembly into multiple configurations. A device students use in multiple configurations would expand the options for open-ended inquiry. Multiple configurations would let chemistry students conduct inquiry-based labs. Students could assemble the appropriates so that they could combine 2, 3, 4 or even more samples.

We know that hands-on experiences improve student learning. In the article Physical Experiences Enhance Science Learning, the authors show that physical experiments lead to increased test scores. Additionally, they showed that later recall of the information activated the brains sensorimotor region. Which suggest a mechanism by which hands-on teaching can improve learning. Since hands-on learning enhances science education, we could argue that the current model where we have a 3-4 credit lecturer class and a one-credit laboratory class is backward and we should be running 3-4 credit labs with one credit lectures or recitations. That, however, is an argument for another day.

Since we know the value of hands-on learning lets takes this idea to the next step. Suppose the students not only ran an experiment to confirm and explore Dalton’s Law but they also built and designed the equipment to do the experiment. Would this enhance learning even more? I could see a couple of ways building your equipment could enhance learning. One, this would be a way to expand the amount of hands-on time. Two, building the test apparatus could give the students a better understanding of how the device works. Three, the designing and building process could potentially lead to enhanced ownership in the experiment. The impact of building your research equipment is an area where more research is needed.

However, even with the evidence that shows hands-on learning enhances science education laboratory classes are under increasing attack. One of the most common arguments I hear against hands-on science education is the cost. The device Cody built for his video is relatively cheap if you were to build it for less then $100 this is less then some microscope slides or chemical reagents. There are of course questions about the equipment used in labs. There are many arguments that the lab is the place for students to learn about research equipment. I have had many discussions concerning the design of laboratory activities that started with “my students need to know how to use X piece of equipment.”

While there are some types of equipment that students should have a familiarity with the idea that students need to learn a specific piece of equipment is ridiculous. First, what is the likely hood that a specific piece of equipment is still going to be in use when they end up working in a research laboratory? Second, what are you trying to teach the students? As an example suppose I design a lab to demonstrate the Mendelian laws of inheritance. The students will need to use a dissecting scope to determine the sex of their fruit flies. Should I devote half the laboratory activities and time to the use of the dissecting microscope? Of course not, the microscope is not part of the principle of inheritance.

Beyond the fixation on specific pieces of equipment, there is also a belief that low-cost equipment is unusable. Whether the cost of equipment affects its educational value is an interesting question. Generally, the cost of equipment is directly related to precision, how much precision do we need. If the purpose of a laboratory activity is to show that acceleration due to gravity is independent of mass, do the student need precision out to 10 decimal places? As long as the equipment meets the need for the activity, we do not need to go with the most expensive thing. When we design STEM activities, we need to focus on the learning goals what has the best chance of enhancing the students learning. In regards to student learning, learning is not proportional to the cost of the equipment, and it is not dependent on a specific piece of equipment. Our instructional design needs to be informed and based on what the research says not ideas about the “best” piece of equipment.

Thanks for Listing to My Musings
The Teaching Cyborg

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