Chromatography - Experiment 4

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.

chrom5
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