Kids, there are many different ways to separate the components of a mixture. This time we will separate the substances used to color candy by using a technique called chromatography. The candy you will need is the brown color of M&Ms©, Reeses's pieces©, and Skittles©.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Use blunt end scissors to cut 3 strips from a cone-type coffee filter that are about 10 cm long and 3 cm wide. Using a pencil, write at the end of each strip the name of one candy. Pour about 1/4 cup of water into a clear plastic cup. Wet one end of a cotton swab and gently wet one side of a candy. Gently rub the candy's wet candy coating onto its filter strip. Make the dark dot on the paper about 2 cm from the unwritten end, in the center. Do not use the dirty end of the cotton swab again. Repeat this procedure for the other two candies, using a clean cotton swab each time. When they are dry, carefully place the strips in the cup of water so that only the very end of each strip touches the water. The end with the writing can be folded over the rim of the cup to keep the strip in place. Be sure the colored dots are above the surface of the water, otherwise all the coloring will simply wash out in the solution.
Observe each strip as the water moves up the paper through the dots. What do you notice happening? Let the water rise nearly to the rim of the cup (this happens naturally by capillary action), then remove the strips and let them air dry. Is the brown color on the candies a mixture of other colors? Compare the colors used for each type of candy, and see in what ways they are the same or different. Each color is a different pigment molecule. Because of the different shape, weight, size, and electric charges on different pigment molecules, they will bind to the paper in slightly different ways. This is how they can separate. Check the ingredients on the candy wrappers to see whether the colors you observed were actually used to color the candies!
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
February 1995
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Reference: WonderScience, volume 8, number 8, December 1994.
