Paper chromatography

Many common materials around us are made up of mixtures of chemicals. Examples are gasoline, ink and the dyes and pigments used in food colouring. Paper chromatography can separate and identify the substances making up these mixtures. Parts of the mixture will separate according to how strongly they are absorbed by the filter paper. Chromatography is used in many different ways, such as in identifying all sorts of substances in police work.

Let's experiment

1. Place several M & Ms or Smarties of the same colour into the saucer with half a teaspoon of water. Mix until the coloured shell has dissolved.
2. Remove the lollies and use a teaspoon to place a very small drop of the coloured water about 1 cm from the bottom of the coffee filter paper.
3. Stand the filter paper in a tall glass filled with two teaspoons of water and a couple of grains of salt. The coloured spot should be above the water line.
4. Watch what happens as the water is sucked up the paper.