Wednesday, July 4, 2012

How Do Fireworks Get Their Colors?

Behind the scenes of the dazzling light shows that spectators ooh and ahh at on the Fourth of July, are carefully crafted fireworks. Whether red, white and blue fountains or purple sparklers, each firework is packed with just the right mix of chemicals to create these colorful lights.

Inside each handmade firework are small packets filled with special chemicals, mainly metal salts and metal oxides, which react to produce an array of colors. When heated, the atoms of each element in the mix absorb energy, causing its electrons to rearrange from their lowest energy state to a higher “excited” state. As the electrons plummet back down to their lower energy state, the excess energy gets emitted as light.

Each element releases a different amount of energy, and this energy is what determines the color or wavelength of the light that is emitted.

For instance, when sodium nitrate is heated, electrons in the sodium atoms absorb the energy and get excited. When the electrons come down from the high, they release their energy, about 200 kilojoules per molecule, or the energy of yellow light, according to the website of the University of Wisconsin-Madison chemistry professor Bassam Z. Shakhashiri.

The recipe that creates blue, for example, includes varying amounts of copper chloride compounds, while red comes from strontium and lithium salts.

Just like paints, secondary colors are made by mixing the ingredients of their primary-color relatives. A mixture of copper (blue) and strontium (red) makes purple.