- In this activity we will use a simple technique to separate the colors from black ink. Because the ink is soluble in water, we will allow the solution to be absorbed on filter paper. As the solvent rises on the paper and evaporates, it leaves the colors in its path.
MATERIALS NEEDED:
Ordinary filter paper or chromatography paper (about 1 cm x 15 cm)
Black felt-tip pens (Flair pens and others)
Test tube
Test tube rack
Paper clip
Cork (to fit test tube)PROCEDURE:
Cut a strip of filter paper or chromatography paper so that it just fits inside a 15-cm (or larger) test tube. Cut a point at one end. Draw a faint pencil line as shown in figure 1. Bend a paper clip and attach it to a cork stopper. Attach the paper strip so that it hangs inside the tube, as shown. The sides of the strip should not touch the glass.
Using a black felt-tip pen, place a small dot on the center of the pencil line.
Add enough water to the test tube to cover the bottom of the filter paper but not enough to reach the ink dot.
Place the filter paper in the test tube with the dot above the water level. Observe. When the water has gone up the filter paper at least 3/4 of the way up, remove the strip and let it dry. Observe the color spots at different heights above the original starting point.OBSERVATIONS:
- Because the ink used in this activity is water-soluble, it dissolves and is absorbed on the filter paper. As the ink rises on the paper, the different colors are deposited according to their degree of solubility in water and their attraction to the paper. The more soluble the color, the further these pigment molecules tend to move up the paper.
What colors separated from the black ink?
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Would other colored inks separate as well? (Try Some.)
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What practical application does chromatography have?
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- Because the ink used in this activity is water-soluble, it dissolves and is absorbed on the filter paper. As the ink rises on the paper, the different colors are deposited according to their degree of solubility in water and their attraction to the paper. The more soluble the color, the further these pigment molecules tend to move up the paper.
PAPER CHROMATOGRAPHY
INTRODUCTION: