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CAIE A Level Chemistry 9701 · Analytical techniques

Analytical techniques: compare question

Compare5 marksStandard

A student separates a mixture of two dyes, P and Q, using thin-layer chromatography. Two separate plates are run, one with a non-polar solvent and one with a polar solvent. The table shows the Rf values obtained.

DyeNon-polar solventPolar solvent
P0.910.22
Q0.100.85

Compare the behaviour of dyes P and Q in the two solvents, and explain the differences in their Rf values in terms of their interaction with the stationary phase (aluminium oxide) and their solubility in the mobile phase.

0 words · 5 marks

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How this question is marked

5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.

Compare means: Give similarities or differences between two things, and say which side each point belongs to. Write each point as a pair, for example: A is X, whereas B is Y. Two separate descriptions rarely earn the marks.

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