AQA · GCSE · Combined Science · Higher

Using Rf to find solvent distance

Q01.4 3 marks

A student calculated the Rf value of a colour to be 0.24

The colour moved 1.8 cm from the start line.

Calculate the distance the solvent moved.

Use the equation:

distance moved by colour

Rf =

distance moved by solvent

Distance moved by solvent = cm 10

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Marking points

1 Substitute into Rf = distance moved by colour / distance moved by solvent: 0.24 = 1.8 / solvent distance.
2 Rearrange to solvent distance = 1.8 / 0.24.
3 Give 7.5 cm.

Full-mark answer

0.24 = 1.8 / distance moved by solvent, so distance moved by solvent = 1.8 / 0.24 = 7.5 cm.