[Image above] Credit: Robert Hensley; Flickr CC BY-NC-ND 2.0
Happy Independence Day to our U.S. readers! Every year, America celebrates the anniversary of its independence from England on July 4, 1776, which became the birthday of the United States of America.
A favorite tradition during the 4th of July holiday is gathering with friends and family at dusk to watch fireworks—those pretty rainbow-colored bursts of sparkling illumination that light up the sky.
Although fireworks are great family entertainment, they can also be dangerous in the hands of amateurs. After all, they are the result of volatile chemical reactions of many different compounds. An average of 250 people end up in the emergency room daily around this time of year with fireworks-related injuries, according to the Consumer Product Safety Commission.
The science behind fireworks
When you consider what fireworks are made of, you might have more respect for the sparklers. Did you know that fireworks are made up of mainly gunpowder?
We can thank our friends in China for their accidental discovery many centuries ago—when they mixed together potassium nitrate, sulfur, and charcoal, which was essentially a recipe for gunpowder.
Other ingredients include dextrin—a binder to hold everything together and reduce sensitivity to impact—and an oxidizing agent of either nitrate, chlorates, or perchlorates to produce the oxygen needed to burn. The ingredients are made into stars that go into the firework tube.
Pyrotechnic stars are small round pellets inside the firework that determine its color and shape when it bursts open. The salts, metal powders, sulfur, and other compounds that make up the stars are responsible for its color. According to a C&EN article, potassium perchlorate (KClO4) is currently used in the formula because of its stability.
Specific colors are determined by different combinations of metal compounds. For example, green is produced by barium salts, such as barium nitrate, barium carbonate, barium chloride, and barium chlorate.
Chemistry teacher Andy Brunning explains that during combustion, electrons in the metal atoms emit excess energy as light as a result of the instability of their excited states. “Different metals will have a different energy gap between their ground and excited states, leading to the emission of different colours,” according to his website.
Another welcome evolution is that over the years, fireworks have actually gotten safer, and scientists recently have been working to make fireworks that are more environmentally friendly.
So now that you have enough pyrotechnics trivia to impress your family and friends tonight during the fireworks show, have a happy and safe holiday—and leave the fireworks deployment to the experts!