Countertop Chemistry Experiment 4
Chromatography of Foods

Chromatography is a separation technique for mixtures. It is based upon the relative attraction of the components of the mixture for the mobile phase (water) and the stationery phase (paper). Separating a mixture of FD&C dyes will allow students to practice this technique.

Materials	Substitutions
filter paper—about 15 cm. in diameter	coffee filters
toothpicks
jar lid – about 4 cm in diameter
petri dishes
food coloring sets-4 vials
Orange Kool Aid
1 lb. bag of M &M's
black transparency pens (optional)
pencil with graphite-based “lead”

Procedure

1. Obtain a piece of filter paper (or a coffee filter) and use a pencil to trace a circle approximately 4 cm. in diameter with the jar lid.
   
   
   
2. Use a pencil to number the areas on the filter paper for each of the substances to be tested. Your teacher will tell you how many positions you will need. Spread the numbers out so that they are equal distances apart.
3. Record the substances to be tested by their appropriate number in the data section below.
4. For each of the substances to be tested, place a small dot on the penciled line by dipping a toothpick into the colored liquid to be tested and touching the paper. Allow the spot to dry, and re-spot it in the same position. (To test the solids, use the directions found in the Teacher’s Notes to prepare the samples).
5. Use the pencil to punch a hole in the center of the filter paper or coffee filter. Insert a folded piece of coffee filter into the hole as a wick.
6. Add water to the petri dish so that it is approximately one-third full. Set the wick into the water with the filter paper resting on top of the disk. Allow the chromatogram to develop. The filter paper itself must NOT touch the water in the petri dish.
7. For best separation of components, remove the chromatogram BEFORE the water reaches the edge of the filter paper (chromatograph). Record the colors in the data table. What trends do you note?(i.e. Are there primary colors in more than one sample?)

Data and Observations

Substance	Center	Middle	Edge

Tape your chromatogram to the back of your lab handout.

Questions

1. What kind of change took place? Was it chemical or physical? How can you tell if the change was chemical or physical? What could you do to test this hypothesis?
2. Why do we use chromatography?
3. How might a chemist use a similar process to analyze a sample containing mixed, colored substances?
4. What do the words heterogeneous and homogeneous mean? How do they apply to the substances in this lab?
5. What are two other mixtures that can be separated by ordinary, physical means?

Teacher's Notes

Directions for mixing food coloring and other substances

CHARTREUSE - 12 drops yellow food coloring & 1 drop green food coloring. Mix and apply to the chromatogram with a toothpick.

TURQUOISE - 5 drops blue food coloring & 1 drop green food coloring. Mix and apply to the chromatogram with a toothpick.

M & M's™ - Place one drop of water on one M & M™, and use the toothpick to apply the coloring from that drop of water. Use either a brown or tan M & M™. Then repeat the process for a green M & M™.

ORANGE KOOL-AID™ - Mix an entire pack of unsweetened Orange Kool-Aid with a few drops of water to make a thick paste. Apply to the chromatogram with a toothpick.

Recommended pens to use for this lab are:
Vis-à-Vis™ transparency pens (black, blue, red, green) and Flair™ black pens.

Results of Chromatographs:

Coloring	Center	Middle	Edge
CHARTREUSE	blue	yellow
BROWN M&M	yellow		red
GREEN M&M	blue		yellow
ORANGE KOOL AID	yellow		red

After every one is through setting up their chromatograms, pass around the M & M's and enjoy!

A sample set up. You can use a cup iinstead of a dish as well.	After a few seconds the water reaches the dyes. All of the dyes in these photos are from M&Ms. Clockwise from the top: orange, blue, green, purple, brown, yellow, red.
After about 5 minutes...	After about 15 minutes...

Answers to questions

1. Chromatography is a physical change. Any of the separated colors could simply be re-mixed in water. Physical changes are reversible.
2. Chromatography is a method of separation for pigments or dyes that shows the different rates of evaporation for the component substances.
3. Chemists can use more complex forms of this method to analyze a sample to determine its contents.
4. Homogeneous matter is the same throughout and exists in only one phase of matter. Heterogeneous matter is composed of a mixture of substances that can usually be seen with the naked eye. Heterogeneous matter can be separated by physical changes.
5. Dissolving the salt in water and filtering the sand from the solution can separate Sand and salt. Evaporation of the water would recover the salt. Colored M & M's™ can be separated by moving the differently colored pieces into separate piles. Student answers will vary.

Safety Precautions

You should monitor the eating of the M & M's™ to be sure that the students are not consuming the ones used for the experiment or ones that have been handled. You might divide the candies by pouring some into a small, paper cup and pass them out to the students.

Disposal

All liquid materials may be poured down the sink. All solid materials should be placed in a solid-waste container.

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