The Colour Splitter

Why it matters

That plain black marker is hiding a secret. Put a dot of its ink on wet paper and watch bands of blue, pink and yellow creep out of it, one colour at a time.

Predict first

A spot of black ink is placed on filter paper and its edge is dipped in water. As the water rises, the ink splits into several colours. What does this tell you about the black ink?

Black ink is really a mixture of different coloured dyes. As water rises up the paper, each dye moves a different distance, so they separate. This method is called chromatography.

• The water changed the ink into new colours
• The black ink was a mixture of several coloured substances — correct
• The ink is a single pure colour
• The paper added its own colours

What you do

Put the steps of paper chromatography in order, from the FIRST step at the top to the LAST at the bottom.

Check yourself

Chromatography is used to separate:

Chromatography separates substances that are dissolved and coloured, such as the dyes in ink, by how far each one travels up the paper.

During chromatography the different colours in ink separate because:

Some dyes are carried further by the rising water than others. Because each colour moves a different distance, the mixture separates into bands.

Chromatography is commonly used to test:

Because it separates coloured substances, chromatography is used to check the dyes in inks, colouring in foods and other coloured mixtures.

• Dissolved coloured substances in a mixture — correct
• An insoluble solid from a liquid
• Iron from sand
• Two solids of different sizes
• Each colour travels a different distance up the paper — correct
• All the colours travel exactly the same distance
• The paper soaks up only one colour
• The colours sink to the bottom
• Inks, dyes and food colours — correct
• The hardness of a metal
• The weight of a stone
• The temperature of water