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CAIE A-Level Chemistry 37.1.2 Interpreting Rf Values

Practise calculating Rf and matching unknown spots to references measured under identical conditions.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • measure from the baseline to each spot centre and solvent front before calculating the distance ratio
  • identify an unknown only by comparing Rf values obtained with the same stationary and mobile phases
  • use agreement in two different solvents as stronger identification evidence than one matching Rf value

37.1.2—Rf values question 1

[Maximum number: 1]

Thin-layer and gas-liquid chromatography can be used to analyse mixtures of substances.

Each type of chromatography makes use of a stationary phase and a mobile phase.

An unknown amino acid is analysed using thin-layer chromatography. Two chromatographs of the unknown amino acid and four reference amino acids, P, Q, R and S, are obtained using two different solvents.

Fig. 6.4

Fig. 6.4

Identify the unknown amino acid. Justify your answer.

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