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How Paper Chromatography Works
Paper chromatography is a method that is used to separate out materials from a mixture. A solvent such as alcohol or water is used to dissolve the components of a mixture. The solvent travels up the paper by capillary action. The particles of solute that are dissolved 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 end up at the top, while the larger particles will travel more slowly and will be seen at the bottom. The pattern on the chromatography paper is called a chromatograph.
This experiment will demonstrate the use of paper chromatography to separate out the colors in the ink of water-soluble markers. A combination of colored dyes is often used to create black ink. Since the inks are water-soluble, water can be used as the solvent to dissolve the ink and separate out the colors. Different brands of marker use various combinations of colored dyes to make up black ink. These dyes create distinctively colored patterns, or chromatographs, when they are separated by chromatography.
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Paper Chromatography Lab Procedure
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
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)