Describe how chromatography works.

Steps to carry out chromatography:

Chromatography is a separation process that looks at how different liquids (in a solvent) travel along a solid (chromatography paper)

● Take a piece of chromatography paper to fit the full length of a boiling tube without touching the sides. Draw a pencil line across the paper about 2 mm from the bottom edge.

● Wearing eye protection, grind a few leaves with a pestle and mortar, adding about 10cm3​ ​of propanone as the solvent. The extract should be as concentrated as possible. The propanone will start to evaporate so you need to work quickly.

● Use a capillary tube to take up a small amount of extract. Place one small drop of this extract in

the centre of the pencil line and allow to dry before adding another drop on top. Build up a

pigment spot that is as small as possible but dense enough that it contains sufficient pigment. Avoid touching the chromatography paper as fingerprints may interfere with the solvent movement.

● Wearing eye protection, carefully pour the chromatography solvent into a boiling tube to a depth of no more than 1 cm. Insert the bung.

● When the chromatography paper has dried, hang it inside the boiling tube by pinning it to the underside of the bung or by trapping it in a split bung. The bottom of the paper should be dipped into the solvent but the pigment spot must not be immersed in the solvent. You want the solvent to be absorbed up the paper and to then travel upwards, carrying any pigment from the extract spot with it.

● The solvent front should rise up the paper, evenly separating out different pigments. When it is close to the top of the tube (after around 10 mins), remove it from the solvent and quickly mark the position of the solvent front using a pencil. Allow the chromatogram to dry in a well-ventilated area, preferably in the dark.

● When dry, examine the chromatogram and calculate the Rf values.

How does chromatography work ?

Is a way of separating a mixture of chemicals which are in a gas or liquid form, by letting them move at different rates.