Paper chromatography

2 marks · Easy

A scientist measures the distance from the pencil line to the centre of a dye spot as 2.5 cm and the distance from the pencil line to the solvent front as 7.8 cm. Calculate the R_f value for this dye. Give your answer to two decimal places.

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0.32 (±0.01)

Common mistakes: Incorrectly dividing the distances

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Marking points

M1 · 1 mark · Sets up calculation for R_f value as (distance moved by spot)/(distance moved by solvent front)

A1 · 1 mark · Correctly calculates R_f value as 0.32 (to two decimal places) (follow-through)

Worked solution

R_f = (distance moved by spot) / (distance moved by solvent front)