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CAIE A Level Chemistry 9701 · Analytical techniques

Analytical techniques: compare question

Compare5 marksStandard

A student carries out thin-layer chromatography (TLC) using a silica gel plate and a non-polar solvent. Two compounds, X and Y, are spotted separately. After development, the solvent front has travelled 8.0 cm from the baseline. Compound X has moved 4.0 cm and compound Y has moved 6.0 cm from the baseline.

Compare the interactions of X and Y with the stationary and mobile phases. Explain how these interactions account for the difference in their retention factors (Rf values).

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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