MadSci Network: Chemistry |
Hi Randi!
The chemical you were watching was Potassium Chlorate (KClO3). Potassium chlorate has many charming features including helping things containing sugar to burst into flame.
Here's what's happening:
Potassium Chlorate is an oxidizer. One
way to think about an oxidizer is to
look at the word. Oxidation can mean
that it adds oxygen to a reaction. This
is not the only or even best definition
for an oxidizer, but I'll use it to
illustrate my point here.
In order to make something burn, you
need three ingredients: stuff that burns
(a fuel), heat, and oxygen to help it.
The potassium chlorate, when it is
placed on the sugary candy, begins
chemically changing the sugar in the
candy. When this happens, a lot of heat
is produced. Now we have two of our
three ingredients to make a fire happen:
sugar (our fuel) and heat (from the
reaction of the potassium chlorate and
sugar). Now, many reactions in nature
produce heat, but will not cause a fire.
One reason is that not enough oxygen is
available to make the fire happen.
Another feature of Potassium Chlorate is
that when it reacts with other
substances, it provides a lot of oxygen
for the reaction (remember the
"oxidizer" part?). If there is already
heat and fuel available, then you have
created a fire.
Potassium chlorate can actually be a fairly dangerous compound to have around; it has been known to "spontaneously" combust, and other nasty reactions can happen with it if you are not careful.
Many science teachers who do a similar experiment to the one you were shown use acid to "spark" the reaction, I imagine that is what happened in your reaction also. The acid (normally sulfuric acid (H2SO4)) reacts with the potassium chlorate to produce a flammable gas (chloric acid as a gas). This helps get the reaction started, normally very slowly leading up to an exciting finish.
Take Care and Be Safe,
Steve E. Williams
Rock Star and Science Demonstrator
Pacific Science Center, Seattle,
Washington
Try the links in the MadSci Library for more information on Chemistry.