Introduction

Colors in candies are due to synthetic dyes that have been approved by the Food and Drug Administration (FDA). Sometimes the colors such as greens and browns are mixtures of several dies. In this laboratory we will separate the colors in M & M® candies and Reese's Pieces® by means of paper chromatography. Differences in the solubilities of the dyes will enable us to make the separation. The more soluble dyes will travel up the paper faster than dyes that are less soluble.

Purpose

To determine if the brown coloring matter in M & M® candies is the same as the brown coloring matter in Reese's Pieces®, at the same time, other candy colors will be chromatographed to determine their component colors.

Safety

• 1. Wear protective goggles throughout the laboratory activity.
• 2. Do not eat any of the candy used in the laboratory activity.

Procedure

1. Obtain 3-4 brown M & M® candies (or whatever color your teacher assigns). Place them in a small evaporating dish and place a few drops of tap water on them. Stir around with a toothpick to dissolve the color. As soon as the colored layer is dissolved, remove the pieces from the dish with forceps and discard them.

2. Repeat with some brown Reese's Pieces® in a second evaporating dish. Use clean toothpicks for each dish.

3. Obtain a piece of chromatography paper that will accommodate spots of both candy colors. Draw a light pencil line about 3 cm from the bottom edge of the paper and initial the paper in one upper corner. Put two pencil dots on the original pencil line, about 3 cm apart. Label one M & M® and one Reese's Pieces®.

4. Using small capillary tubes place spots of each color on the labeled dot. The spots should be about 1 cm in diameter, andmust not overlap. Let dry and apply more sample, keeping the spots as small as possible. Repeat until you have placed about 5-6 spots on each dot to make a concentrated sample.

5. Obtain the proper container for the chromatography (beaker or jar) and pour in salt solution until it is about 1 cm deep. Suspend the paper in the container as your instructor directs(see Forensic Chemistry module, Activity 1). Be sure that the lower end of the paper is just touching the solution, and that the solution does not reach the colored spots.

6. When the solution rises to within 3 cm of the top of the paper, remove the paper from the solution and allow to dry. Mark the position of the solution on the paper with a light pencil line.

7. Compare the chromatograms for each dye to determine if the candies contain the same dyes.

8. Thoroughly wash your hands before leaving the laboratory.

Data Analysis and Concept Development

Notice the number and colors of the spots on the two chromatograms. Draw circles around the spots that are common to the two candies. The spots must be the same color and must have traveled the same distance up the paper.

• 1. Is a pure brown dye used to color the candies?
• 2. If you wished to produce a green dye, what colors would you use?
• 3. Suppose you were given an unmarked bag of one of these candies. How could you distinguish chemically whether the contents were M & M's® or Reese's Pieces®?

Implications and Applications

• 1. How could chromatography be used to distinguish some look-alike candies?
• 2. How could you tell which dyes were present in the candies?

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