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CAIE A-Level Chemistry A2 37.2.3 Retention Times Questions

Practise explaining why components have different GLC retention times through stationary-phase interactions.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • link a longer retention time to stronger attraction or intermolecular forces with the stationary phase
  • link a shorter retention time to weaker stationary-phase interaction and more time in the moving gas
  • compare the components named in the question rather than treating retention time as a fixed molecular property

CAIE A-Level Chemistry A2 37.2.3 Retention Times Questions question 1

[Maximum number: 2]

An alkene, a carboxylic acid and a ketone, all of similar volatility, are mixed together. The mixture is then analysed by gas chromatography.

The gas chromatogram produced is shown.

Figure for Question CAIE A-Level Chemistry A2 37.2.3 Retention Times Questions question 1 — CAIE A-Level Chemistry A2

The separation of the three compounds depends on their relative solubilities in the liquid stationary phase. The liquid stationary phase is an alkane.

Complete the table to suggest which compound in the mixture is responsible for each peak J, K and L. Explain your answer by reference to the intermolecular forces of each compound.

Table for Question CAIE A-Level Chemistry A2 37.2.3 Retention Times Questions question 1 — CAIE A-Level Chemistry A2

A student calculates the areas underneath the three peaks in the chromatogram.

Table for Question CAIE A-Level Chemistry A2 37.2.3 Retention Times Questions question 1 — CAIE A-Level Chemistry A2
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