There are many ways modern man has learned to combine chemicals to make life easier, but it is not always good to combine them. There is a great deal of danger in mixing the wrong ones together, but students might not remember that if they are not paying attention. Giving them live demonstrations of the effects of putting two chemical together can be a good lesson they will carry with them for a lifetime.
Adding different chemicals together produces a variety of results, and many educators begin by teaching students how to write formulas. Some chemicals, inert on their own, will activate a catalytic reaction when combined with others. Teaching students how these reactions occur can give them insight into the dangers of the reactions, or it could help them understand how a mixture can form a useful bond. While safety is always important, teaching them the correct way to perform these types of experiments might keep them even safer in the future.