This experiment needs to be
carried out under adult supervision as it involves fire and heating
materials which can burn or explode. Have you ever wondered how they
get the different colours into the fireworks? If you want yellow
fire, do you add yellow paint to the mixture? No, that would not work.
To see how the colours get into fireworks, you will need:
metal paperclips pliers boric acid (from the pharmacy) creme of tartar (from the grocery) salt water a clear, blue flame. If you have
a gas stove, the burner will work very well. If not, you can use a
candle, but the colours will be more difficult to see.
Please read the safety warning
before you start. 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 and 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 the 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 colour of
a candle flame is caused by the burning of tiny bits of the
element carbon. 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 colours. The yellow
colour 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 contain the element sodium.
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. Bright whites are produced by burning aluminum or magnesium
metal. 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
marvellous chemistry show at the same time.
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these
experiments on my web site.
