Coffee Filter Chromatography

In keeping with the spirit of National Chemistry Week, try a chemistry project safe for all ages that can be done using supplies easily found at home. You can gather a collection of different colored fall leaves and take a close look at the pigments that give them their colors. In particular, this is interesting if you can get different colors of the same type of leaf.

If the leaves are dried, you can use a coffee grinder to chop them. Use a coffee grinder or a blender to puree living leaves. If you can, try to transfer the pigments into alcohol by allowing crushed leaves to sit in a very small volume of alcohol (vodka or rubbing alcohol are good choices) until the liquid has picked up as much coloration as possible. Paint the edge of a strip of coffee filter with the colored alcohol and watch the pigments separate as the mixture is pulled across the filter.

This is a form of paper chromatography, used to separate molecules according to their size. Smaller molecules will move more quickly across the paper than larger molecules, so the pigments you see furthest from the painted section of paper are smaller molecules than the bands of color that stay closer to the origin. You can compare the compositions of different leaves or different colors of the same leaves by running the alcohol mixtures side-by-side on a coffee filter or by painting separate filters with the mixtures. You may want to keep the origin point damp with alcohol, or else the separation will end when the solvent has evaporated.
Coffee Filter Chromatography | Chemistry How-To Guide