Fireworks play a role in many holidays and celebrations. Have you ever wondered how they get the different colors into the fireworks? If you want yellow fire, do you add yellow paint to the mixture? No, that would not work. Instead, you need something that will burn with a yellow flame. Yellow flames are fairly common, but what about green flames or purple flames?
WARNING! This experiment uses fire. Be very careful and safe.
To see how the colors get into fireworks, you will need:
- metal paperclips
- boric acid (from the pharmacy)
- creme of tartar (from the grocery)
- a clear, blue flame. If you have a gas stove, the burner will work very well. If not, you can use Sterno or something similar
Straighten several of the paperclips into long, straight wires. Dip the end of one of the wires into the water and then into the salt. Some of the salt should stick to the wire. Hold the other end of the wire with the pliers, so you don't burn your fingers. Place the salted end of the wire into the flame. The flame should change to a bright yellow. Dip the hot wire into the water, so you don't accidentally burn yourself. Select a new wire and repeat the experiment with fresh water and some boric acid powder. The flame should turn green. Try the creme of tartar and the flame will be lavender.
What is happening? Most of the light that comes from a flame is caused by solid particles burning inside the flame. As we have seen in past experiments, the yellow color of a candle flame is caused by tiny bits of the element carbon burning with glowing combustion. The blue flame that we started with does not contain solid particles, so it gives off very little light. By adding chemicals to the flame, we can give it different colors.
The yellow color caused by the salt is due to a chemical called sodium. The boric acid contains boron, which produces green and the creme of tartar contains potassium, which burns with a lavender light.
This idea also applies to fireworks. When you see yellow fireworks, they can be made with the element sodium, but they can also be made by using powdered iron (see How They Get the Sparks in a Sparkler).
Calcium salts are added to produce orange. Salts of strontium or lithium are used for red, and you get green by adding barium, boron or copper. Copper chemicals can also be used to produce a blue color. Bright whites are produced by burning aluminum or magnesium metal. Other chemicals are added to make the colors brighter or deeper. Fireworks companies keep their exact formulas secret, and an expert can often tell who made a firework by the exact color of blue, green, etc. which a firework burns.
The next time you are "ooohing" and "aaaaahhing" over a fireworks display, keep in the back of your mind that you are also seeing a marvelous chemistry show at the same time.