Chemistry Required Practical: Paper Chromatography

GCSE Chemistry Required Practical - Paper Chromatography

Investigate how paper chromatography can be used to separate and tell the difference between coloured substances. Students should calculate R_f values.

Paper chromatography is the separation of mixtures of soluble substances by running a solvent (mobile phase) through the mixture on the paper (the paper contains the stationary phase), which causes the substances to move at different rates over the paper

In this practical students use paper chromatography to separate and identify a mixture of food colourings.

Method:

1. Use a ruler to draw a horizontal pencil line 2 cm from the bottom short edge of the chromatography paper. This is your origin line.
2. Mark five pencil spots at equal intervals across the origin line. Make sure you keep at least
3. 0.5 cm away from each edge of the paper.
4. Use a glass capillary tube to put a small spot of each colouring A, B, C and D on four of the pencil spots. Use a different tube for each colouring. Use the fifth tube to put a small spot of the unknown mixture U on the fifth pencil spot. Try to make sure each spot is no more than 2-3 mm in diameter. Label each spot in pencil.
5. Pour water into the beaker to a depth of no more than 1 cm.
6. Clip the top short edge of the chromatography paper to the wooden spill. The top end is the end furthest from the spots.
7. Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper should dip into the water solvent.

Paper Chromatography - GCSE Science Required Practical
How to separate substances using chromatography and measure R_f values.

00:00 Preparing experiment
06:33 Analysing results
07:57 Calculating R_f value

GCSE Chemistry Required Practical: Chromatography

How to use paper chromatography to identify the colours in a sample of food colouring?

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Check out the sample question and solution on Sample Assessment Material (page 56).
This example is taken from the sample assessment material, paper 1CH0/1H, Q1.

Mixtures of coloured substances can be separated by paper chromatography.
(a) Paper chromatography was used to separate a mixture of blue and red inks.

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