CAIE A Level Chemistry 9701 · Analytical techniques
A sample containing three organic compounds is separated by gas-liquid chromatography. The chromatogram shows three peaks. The first peak has a retention time of 1.8 minutes and the third peak has a retention time of 6.4 minutes. Explain, in terms of the stationary phase and the mobile phase, why the three compounds have different retention times.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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