Laboratory Activity: Teacher Notes

Major Chemical Concept

Paper chromatography can be used to separate the food colors in candy such as M & M® candies and Reese's Pieces®, and can show the differences between the brown colors in the two brands.

Level

This activity is appropriate for all levels of chemistry classes.

Expected Student Background

None

Time

50-55 min. The activity can be broken into two 30-min. time periods by doing Steps 1-4 on the first day and storing the prepared samples for later use.

Safety

Read the Safety Considerations in the Student Version.

Materials (For 24 students working in pairs)

Nonconsumables

• 12 Chromatography jars with lids or stoppers (empty 12-16 oz jelly or spaghetti sauce jars)
• 12 Forceps
• 12 Lead pencils
• 12 Ringstands and buret clamps

Consumables

• 36-48 Pieces of each color and kind of candy
• 12 Chromatography paper (or filter paper) pieces cut to fit containers to be used (e.g., 4 cm x 8 cm
• 24 Capillary tubes
• Water, distilled
• 0.1% NaCl solution (dissolve 0.5 g NaCl in about 500 mL water)

Advance Preparation

Obtain the necessary amount of candy. Cut chromatography paper to fit containers. Prepare suspension apparatus for chromatography jars or tubes. A paper clip hook inserted in a cork is ideal for large test-tubes (see Forensic Chemistry module for diagram). Have a sample setup ready for students to use as a model.

Pre-Laboratory Discussion

Show an example of a chromatographic separation (such as ink from a washable black marker or pen), and explain how paper chromatography can separate the colors. For use in foods, there are only 5 or 6 artificial colors that are approved by the Food and Drug Administration (FDA). A mixture of colors is required to give a brown color. Show students the candy and ask them if they think that the brown colors in each brand are made of the same mixture of colors. Paper chromatography will provide the answer.

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