The World's Biggest Flame Test....
Most chemistry teachers I know do flame tests with their students. It ties in well with many topics, is colorful and the kids enjoy seeing the colors and burning stuff. There are many applications. For years I always mentioned that astronomers use the idea of the flame test. They simply look at stars and examine the spectra from the light of these stars. They then match the spectra with the elements and then they can see and infer what elements are millions of light years away. I always mentioned this but never was able to demonstrate it.