Before we started with the experiment I showed these videos from youtube.
and this video from a class room in Greece.
Quite a few of these demonstrations made use of catalysts to speed up chemical reactions. The lab, Chapter 6, Lesson 5: A Catalyst and the Rate of Reaction in the American Chemical Society’s middle school curriculum starts by asking students how they knew chemical reactions were taking place (there are links to two videos in the actual curriculum) in demonstrations they were shown. Most of the kids immediately answered ‘bubbles’ or ‘gas was made’. The two demonstrations shown both involve the break down of hydrogen peroxide into water and oxygen. Hydrogen peroxide will break down all by itself but its a fairly slow reaction so adding a catalyst can speed this up considerably. I used snatoms to basically act out how a catalyst (Platinum) help break carbon monoxide and oxygen up so it can form carbon dioxide – check out this page for a great graphic showing this reaction. With the snatoms I could put the molecules on a white board and move them around and at the end show the catalyst atoms didn’t move or change so we leave them out of the chemical equations.
For the lab, the kids put 10 ml of hydrogen peroxide (3 percent like you can buy at the grocery or drug store) into a graduated cylinder, then 1 drop of dish detergent solution (to help make bubbles). Nothing really happens at this point but they should stop to notice that fact before they put a small amount (1/4 to 1/2 tsp) of yeast into the cylinder. They swirl the cylinder a bit to help mix ingredients and then watch the bubbles form. There are questions to answer on the lab handout – how do you know a chemical reaction was taking place? what was used a catalyst? etc.
The second part of the lab used copper II sulfate solution to react with aluminum foil. Usually this would be a very slow process because of an oxide layer on the foil, but once they put a small amount of table salt in the beaker, the reaction becomes quite vigorous. The salt helps to destroy the oxide layer so the copper sulfate can reach the aluminum more readily. Very quickly the foil turns a copper color (photo below right) and then a few minutes later it disintegrates. The cup also got very warm (almost 50 Celsius).
These were both pretty quick experiments so we had some time left over to make elephant toothpaste.