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CAIE A-Level Chemistry A2 37.1 Thin Layer Chromatography Questions

Practise identifying TLC phases, calculating Rf and interpreting spot movement against reference samples.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • identify the solid stationary phase, solvent mobile phase, baseline, spots and solvent front on a plate
  • calculate Rf as distance travelled by the spot divided by distance travelled by the solvent front
  • match an unknown to references under the same conditions and explain solvent-polarity effects on movement

Covered syllabus points

37.1.1—And understand the terms37.1.2—Rf values37.1.3—Differences in Rf values

Question 1

[Maximum number: 3]

A student uses thin-layer chromatography (TLC) to analyse a mixture containing different metal cations. The student repeats the experiment using different solvents.

Fig. 6.1 shows the chromatogram obtained by the student using water as a solvent.

Fig. 6.1

Fig. 6.1

Question (a)

(a)

Suggest a compound that could be used as the stationary phase in this experiment.

[ 1 ]

Question (b)

(b)

Table 6.1 shows the RfR_{\mathrm{f}} values for different metal cations when separated by TLC using water as a solvent.

Table 6.1

Table 6.1

Suggest the identity of the cation that causes the spot at M in Fig. 6.1.

Explain your answer.

[ 1 ]

Question (c)

(c)

The student repeats the experiment using butan-1-ol as a solvent.

The metal cations do not travel as far up the TLC plate in this experiment.
Suggest why the metal cations do not move as far up the TLC plate with butan-1-ol as a solvent.

[ 1 ]

Question 2

[Maximum number: 2]

Tyrosine and lysine, shown in Fig. 9.1, are naturally occurring amino acids found in proteins.

Fig. 9.1

Fig. 9.1

Question (a)

(a)

A mixture of tyrosine and lysine can be separated by thin-layer chromatography. Under certain conditions the RfR_{\mathrm{f}} value of lysine is 0.14 and the RfR_{\mathrm{f}} value of tyrosine is 0.45 .

[ 2 ]

Question (i)

(i)

Explain what is meant by RfR_{\mathrm{f}} value.

[ 1 ]

Question (ii)

(ii)

Suggest an explanation for the difference in RfR_{\mathrm{f}} values.

[ 1 ]

Question 3

[Maximum number: 2]

Question (a)

(a)

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.

[ 2 ]

Question (i)

(i)

Complete Table 6.1 with an example of each of these.

Table 6.1

Table 6.1

[ 1 ]

Question (ii)

(ii)

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.

[ 1 ]

Question 4

[Maximum number: 1]

A student uses thin-layer chromatography (TLC) to analyse a mixture containing different metal cations. The student repeats the experiment using different solvents.

Fig. 6.1 shows the chromatogram obtained by the student using water as a solvent.

Fig. 6.1

Fig. 6.1

Suggest a compound that could be used as the stationary phase in this experiment.

Question 5

[Maximum number: 1]

A student uses thin-layer chromatography (TLC) to analyse a mixture containing different metal cations. The student repeats the experiment using different solvents.

Fig. 6.1 shows the chromatogram obtained by the student using water as a solvent.

Fig. 6.1

Fig. 6.1

Table 6.1 shows the RfR_{\mathrm{f}} values for different metal cations when separated by TLC using water as a solvent.

Table 6.1

Table 6.1

Suggest the identity of the cation that causes the spot at M in Fig. 6.1.

Explain your answer.

Question 6

[Maximum number: 1]

A student uses thin-layer chromatography (TLC) to analyse a mixture containing different metal cations. The student repeats the experiment using different solvents.

Fig. 6.1 shows the chromatogram obtained by the student using water as a solvent.

Fig. 6.1

Fig. 6.1

The student repeats the experiment using butan-1-ol as a solvent.

The metal cations do not travel as far up the TLC plate in this experiment.
Suggest why the metal cations do not move as far up the TLC plate with butan-1-ol as a solvent.

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