This week's experiment is one that was mentioned on one of the museum education e-mail lists. It started as a fun experiment and a wonderful excuse to buy some chocolate candy. As I went along, I saw several marvelous aspects to the science.
To try this, you will need:
Put about an inch or two of warm water into the bowl. Select several candies that have nice, clear "M"s on them. Place them, M side up, in the water. Now watch carefully. Quickly, the candy coating starts to dissolve and the colors settle to the bottom around the candy. The last part of the color to go will probably be the part under the M. Slowly, a thin film with the M on it will separate from the candy and float to the surface. If you let the candy continue to dissolve, you will see a white candy layer under the colored one and finally the chocolate center becomes visible.
I could not collect enough of the film that the M is printed on to be certain, but it seems to be a very thin film of wax. It floats in water, does not dissolve and leaves a waxy smear on a clean glass. Wax is also edible, which is important with candy. You might try to think of other ways to tell if it is wax or something else.
The M itself is made of titanium oxide, which is mined very near my home. The sand in this part of Florida contains heavy, dark grains as well as the white sand. These dark minerals contain titanium and they are mined by RGC Minerals and used to make the titanium oxide that is used for the Ms on these candies.
I found it very interesting that the dissolved colors stayed separate and formed very sharp boundaries. I tried the experiment again with cold water and found the color separation even more striking. Placing different colors in a circle around the edge of the bowl formed triangular color segments that looked like an artist's color wheel. The chemicals which produce the colors have different densities. In past experiments we have separated these colors by placing wet M&Ms on a coffee filter and watching the colors separate through a process known as chromatography. I find it even more interesting to see the colors forming such sharp boundaries in the water. I plan to do some more investigation on this, so if you have any additional information about it, I would love to see it.
There are all sorts of things you can try to take this farther. You might try seeing how the temperature of the water changes the rate that the candy dissolves. If you have a test tube or a very thin bud vase, try stacking different colored candies and covering them with water to see if the colors will form separate layers one on top of the other.
As you know, I always like to conserve and recycle the materials for the experiments. When you finish, the candy is still perfectly edible, so don't waste it. Just drain off the water and then scoop up the lumps of chocolate for a snack.
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