One of the reasons that I love teaching Chemistry is that you get to do so many awesome experiments. Not only are they cool, but they provide a great hook for students as a means of introduction to a new topic. The reaction between potassium iodide and lead nitrate is a great demonstration to introduce students to the idea of solubility. They each start off as a colorless solution when dissolved in water, but when you mix them together you end change. This reaction also demonstrates a double replacement reaction. The pricipitate of lead (III) iodide is insoluable in water, but when heated it become slightly soluable while allows that lead (III) iodide to dissociate and the solution turns colorless again. Its a great reaction. Below is a great image from Compound Chem that gives a vidual to the quick explaination I gave above. This is a great site for any chemistry teacher to check out even if this demo doesn't fit it what you are doing.
