In today’s class we did Chapter 6, lesson 1: What is a Chemical Reaction from the American Chemical Society’s Middle School Chemistry curriculum. This lab starts by demonstrating combustion by burning a candle and then putting a jar over it to extinguish the flame. We had already done an earlier lab on combustion, so the kids already knew the reaction needed oxygen and fuel and produced water and carbon dioxide. We then looked at the reaction of methane and oxygen molecules to form carbon dioxide and water. I had the students build models of the reactants with Snatoms or Zoomtool, then take them apart
and build the products from the same pieces. I tried to make a point of showing how everything got used up to make the products, so no atoms were created or destroyed in the reaction, just rearranged. This is the first time I’ve used the Snatoms and I really like them. They go together much easier than the zoomtools since they use magnets. The small black bars represent double bonds in the oxygen and carbon dioxide molecules.
Once the students had done the models they colored the paper atoms from the curriculum and cut and paste them into their notebooks to show the reactants and products. They then filled out three tables, each one a different combustion reaction, where they had to figure out how many carbon, oxygen and hydrogen atoms were on the reactant side and how many were on the product side of a chemical reaction. This helped drive home that you have to have the same number of each type of atom on both sides.
After everyone was done with the paper work we went outside for a demonstration. I cut very thin strips of aluminum foil and placed them in a test tube. Then I poured muriatic acid (HCl), which you buy at a pool store, into the test tube. It takes a few minutes but you will start to see bubbles rising from the aluminum foil as the Al and HCl produces hydrogen gas. Eventually it becomes come vigorous and the liquid turns dark grey (AlCl3 in soln) and suddenly the foil is gone!