Paper chromatography

Atomic structure

What is paper chromatography used for?

Separating mixtures of soluble substances. Often food colourings, inks, dyes or plant pigments.

First step of paper chromatography

Ink or plant dye is dotted along the pencil line

Second step of paper chromatography

As the paper is lowered into the solvent, some of the dye spreads up the paper.

Third step of paper chromatography

The paper has absorbed the solvent, and the dye has spread further up the paper.

What is the stationary phase?

The absorbent paper.

What is the mobile phase?

The solvent that moves through the paper, carrying different substances with it.

What causes the dissolved substances to move at different rates through the paper?

They are attracted to these 2 phases in different proportions.

What can a chromotogram be used for?

Distinguishing between pure and impure substances.

What does a pure substance look like on a chromotagram?

It produces one spot on the chromotagram.

What does an impure substance look like on a chromotagram?

Produces two or more spots.

How can a chromotogram be used to identify substances?

By comparing them with known substances.

How do you know if two substances are likely to be the same from a chromotagram?

• They produce the same number of spots, and they match in colour.

• The spots travel same distance up the paper.