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CAIE A Level Chemistry 9701 · Analytical techniques

Analytical techniques: compare question

Compare7 marksChallenge

A mixture of two isomeric alcohols, butan-1-ol and butan-2-ol, is separated by gas-liquid chromatography. The stationary phase is a high-boiling-point non-polar liquid coated on a solid support, and the mobile phase is an unreactive gas. The column is held at a constant temperature. Butan-1-ol has a longer retention time than butan-2-ol.

Compare the two isomers in terms of their interaction with the stationary phase, and explain why butan-1-ol has the longer retention time. In your answer, refer to the role of the stationary and mobile phases.

0 words · 7 marks

No account needed for your first marks. Your answer is used only to mark it.

How this question is marked

7 marks, so the mark scheme is looking for about 7 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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