Kitchen Chemistry Experiment 4
Chromatography of Foods

What is chromatography? What kinds of substances have colorings in them? How can the mixtures of dyes be separated and identified?

 

Materials	Substitutions
Large filter paper	coffee filters
round toothpicks
jar lid
petri dishes
food coloring sets-4 vials
Purple Saurus Rex & Orange Kool Aid
1 lb. bag of M &M's
black transparency pens (optional)

Procedure

1. Obtain a coffee filter and use a pencil to trace a circle with the jar lid.
2. Use the pencil to number the spots 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. If you are instructed to use a water soluble pen, place a small dot on the penciled line. Allow the spot to dry and respot in the same position.
5. Your teacher will instruct you on the other substances to be tested.
6. Use the pencil to put a hole in the center of the coffee filter. Insert a folded piece of coffee filter into the hole as a wick.
7. Add water to the petri dish so that it is a third full. Set the wick into the water and allow the chromatogram to develop. The coffee filter itself must NOT touch the water in the petri dish.
8. Remove the chromatogram BEFORE the water reaches the edge of the coffee filter. If you wait too long, it will be difficult to see all the component colors present. Record all the primary colors in the data table below

 

Data and Observations

Substance	Center	Middle	Edge

Tape your filter paper to the back of your lab handout.

Extensions

1. What kind of change took place? Was it chemical or physical?
2. How can you tell if the change was chemical or physical? What could you do to test this hypothesis?
3. Write a definition of chromatography.
4. How could this be a useful type of analysis for a chemist? How might a chemist use a similar process to analyze a sample?
5. What do the words heterogeneous and homogeneous mean? How do they apply to the substances in this lab?
6. What are 2 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 paper strip with a toothpick

TURQUOISE-5 drops blue food coloring & 1 drop green food coloring.

M & M's-Place one drop of water on one M & M and use the toothpick to pick up the coloring from that drop of water. Use a brown or tan M & M then repeat process for a green M & M.

PURPLE SAURUS REX-Mix an entire packet of unsweetened Kool Aid with a few drops of water to make a thick paste. Apply to the paper strips with a toothpick.

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

 

Recommended pens to use for this lab are:

Flair black, Sanford's Big Sig, Pilot Precise Rolling Ball, USA Expresso, or any black transparency pens.

 

COLORING

Color	Center	Middle	Edge
CHARTREUSE	blue		yellow
BROWN M&M	yellow		red
GREEN M&M	blue		yellow
PURPLE SAURUS REX	blue		red
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 instead 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
2. Any of the separated colors could simply be remixed in water. Physical changes are reversable.
3. Chromatography is a method of separation for pigments or dyes by using different rates of evaporation for the component substances.
4. Chemists can use more complex forms of this method to analyze a sample to determine its contents.
5. Homogeneous matter is the same throughout and in only one phase of matter. Heterogeneous matter is composed of a mixture of substances that can usual been seen with the naked eye. Heterogeneous matter can be separated by physical changes.
6. SAND AND SALT could be separated by dissolving the salt in water and filter the sand from the solution. Evaporation of the water would recover the salt. COLORED M & M'S can be separated by visually moving the different colored candy pieces into separate piles.

 

 

 

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 in any way. You might divide the candies by pouring some into a small bathroom paper cup and pass them out to the students.