Filling the time between the end of course exam and finals is always a challenge. I have been using this week to catch up on a few of my favorite labs that didn't quite fit in with the modeling curriculum. Today, we did flame tests.
I'm not sure if flame tests are included in the later units of the modeling curriculum. The level 1 chemistry modeling workshop only goes through the core units and doesn't cover the current model of the atom. I had to rush through the model of the atom so quickly before the EOC that I barely looked at the lesson plans for those later units. But I was sorry we didn't get to this lab, since it is always a hit with the students.
I usually do it as an "identify the unknown" lab: I give the students a list of ionic compounds and the color flame that each compound produces. Then I give them about 6 very benign "unknowns" to identify (in the numbered weighing dishes in the picture). I put a beaker of wooden splints soaked in DI water at the table and just have them dip a splint into a compound and hold it in the flame. The burners don't get quite as crusty using the wooden splints as they do when using wire loops, and the disposable splits prevent cross contamination. This method seems to produce the best colors for me, safely, with minimal prep and minimal wastage of chemicals.
Tomorrow, I'm thinking we might make rock salt ice cream. In the past, I've done it with ice/rock salt and I've done it with dry ice. The dry ice is fun, but it can be a pain to deal with since I have to pick it up on my way to school. And one year I had a student manage to somehow get a piece of dry ice down their sock and irritate their skin. I'm not even kidding!
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