Tag Archives: teaching on a budget

How to measure oxygen

I wanted my honors chemistry students to see how chemists of old discovered the make-up of water using test tubes, batteries, and pushpins. The process would allow students to measure the amount of gas produced in each test tube and see it was a two:one ratio. All of this sounds great. Until I tested it out for myself…

The brass pushpins made hydrogen gas ok, but I couldn’t get oxygen. The silver ones worked a little better, but I still wasn’t able to produce oxygen gas. I tried salt water, I tried baking soda in water. I tried vinegar in water. I spent 3 straight mornings not grading or helping students, but trying to figure out this stupid lab. Jus when I was ready to give up, I found a site that reminded me graphic conducted electricity. So I made graphite water electrolysis devices.

Step one: poke holes in plastic cups.

Step two: insert pencil lead into said holes.

Step three: Use paraffin wax to secure the pencil lead.

Step four: Make thirteen more so that every pair can have one.

Step five: Test it to make sure it works

Step six: Cry when your 3rd hour class breaks the lead on half of them and you have to spend half of your lunch fixing them.

Step seven: Find out how much this set-up costs on Flinn Scientific and add it to you list for next year.

All and all I don’t think a single student got the 2:1 ratio of hydrogen to oxygen but they had a lot of fun setting it up and breaking apart the water. We’ll leave discussing just what the heck happened to Monday when I’m less frazzled from helping them set up the stupid thing correctly.

Oh, and if anyone knows a better solution to use besides salt, baking soda, or vinegar, please let me know in the comments!

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