Paper chromatography is a method to separate out materials from a mixture. A solvent travels up the paper by capillary action. Solutes that dissolve in the solvent are carried up the paper along with the solvent. The particles of solute will be separated according to size as they are carried up the paper; the smaller particles travel faster and will be at the top, while the larger particles will travel more slowly and will be seen at the bottom.
Some inks are water-soluble, so water can be used as the solvent. Different brands of marker use different combinations of colored dyes to make up black ink. These different dyes create distinctively colored patterns when they are separated by chromatography. The pattern on the chromatography paper is called a chromatograph.
Materials:
Several different brands of black water-soluble markers (Sharpies will not work, they are not water-soluble)
Coffee filters cut into strips approximately 1 inch wide and 5-6 inches long
Paper or plastic cups
Pencils
Tape
Water
Method:
Choose three different brands of black marker
Write each brand name at the top of a paper strip in pencil.
Make a horizontal line with the marker approximately 1 inch from the bottom of the paper strip
Attach the top of the paper to a pencil with tape.
Put water in the paper or plastic cup to a depth of approximately 1/2 inch.
Lay the pencil across the top of the cup so that the paper strip hangs down into the water, but make sure that the bottom edge of the strip barely touches the water. The ink line should not be in the water.
Allow the water to travel up the paper for several minutes. The ink will become blurred, and the different dyes in the ink will separate.
The result will be a pattern of different pigments, and the pattern will be different for each brand of marker, because they use different combinations and colors in their ink.
Let the paper strips dry and staple them to the data sheet.
If there is time, students can try it with other colored markers besides black.
Have students answer the following questions on their data sheet:
1. What colors make up the black ink?
2. Were the colors different for the different brands of marker you tested? Describe the colors you saw for each brand of marker.
3. What is the solvent? (water)
4. What is the solute? (the dyes in the ink)
