Pyrotechnics
Like many other Americans, I watched a fireworks display earlier this month when our country celebrated Independence day. The display was impressive, with so many colors and patterns to behold. After I became a chemistry professor I noticed a change in the thoughts running through my mind as I watch the colorful explosions. What combinations of salts, fuels, and oxidizers are used to create the different patterns of flashes and streaks that shoot through the air? I recently read an article in C & E News that helped answer some of my questions on the subject. (As you may notice, the article itself isnt’ recent, but I sometimes get behind on my reading…..)
When I teach general chemistry or chemistry for liberal arts majors, I usually do a demo that I think of as flames with salts. It involves several Petri dishes with different salts in them, into which I pour methyl alcohol. Then I set the methanol on fire. The methanol flames show different colors due to the salts. My favorites are strontium (red), boron (green), and copper (green). I perform this demo when we’re talking about Bohr’s model of the atom, because it was this kind of experimental evidence that Bohr sought to explain with his model.
The C&E News article doesn’t talk about the Bohr model, though. It discusses the pollutants released from fireworks displays and how chemists are trying to make safer chemicals so that we don’t wind up polluting our environment. As it turns out for most once-a-year displays, the trace pollutants don’t add significantly to what is already in the environment (other than the smoke and particulate matter in the air immediately following the display). More significant problems occur when fireworks are used indoors or in places like Disneyland, where the fireworks displays occur on a regular basis. Disneyland’s neighbors in Anaheim complained, and the folks at Disneyland sought advice from Los Alamos National Laboratory. The engineered solution involved using compressed air to shoot the fireworks up, minimizing the need for black powder for that job. Thus, there was less smoke and the neighbors were happy.