Paper Chromatography

This lesson covers the principles, method and interpretation of paper chromatography, as required by the Edexcel GCSE Chemistry specification (1CH0, Topic 1). Paper chromatography is used to separate and identify dissolved substances. It is one of the Edexcel core practicals, so you need to know the method in detail and be able to calculate and interpret Rf values.

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What Is Chromatography?

Chromatography is a technique used to separate a mixture of dissolved substances. It works because different substances have different solubilities in a given solvent, and therefore travel different distances through the chromatography paper.

The Principle

The separation depends on two things:

1. The attraction between the substance and the paper (the stationary phase) — substances that are more strongly attracted to the paper move more slowly.
2. The attraction between the substance and the solvent (the mobile phase) — substances that are more soluble in the solvent are carried further.

A substance that is very soluble in the solvent and not strongly attracted to the paper will travel a long way. A substance that is not very soluble in the solvent and strongly attracted to the paper will travel only a short distance.