Gas/Liquid Chromatography | CIE A Level Chemistry Exam Questions 2025

1a3 marks

This question is about gas chromatography.

Name the three types of chemical that gas chromatography is used for.

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1b2 marks

Silica and alumina are commonly used as the stationary phase in thin layer chromatography.

State the type of chemical that is commonly used as the stationary phase in gas chromatography.

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1c2 marks

State the type of chemical that is used for the mobile phase in gas chromatography. You should include at least one specific example in your answer.

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1d4 marks

Results in gas chromatography are based on retention time.

i)

Define the term retention time.

[1]

ii)

State three factors that retention time depends upon.

[3]

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1e1 mark

State what information the relative size or area under the peak on a gas chromatogram provides.

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1f3 marks

Gas chromatography is carried out using a polar stationary phase and argon as the carrier gas.

Use the chromatogram in Fig. 1.1 to answer the following questions.

Fig. 1.1

i)

State which compound has the lowest retention time.

[1]

ii)

State which compound is the least polar.

[1]

iii)

State which compound has the greatest interaction with the stationary phase.

[1]

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1a3 marks

Gas chromatography is often connected to mass spectroscopy in order to analyse each compound as it exits the gas chromatography column. This combined technique is called GC-MS.

The gas chromatogram of an organic mixture is shown in Fig. 1.1. The stationary phase is a polar, high-boiling point liquid on a solid support.

8-1-3a-h-gas-chromatogram

Fig. 1.1

i)

Name an appropriate mobile phase that could be used to form this gas chromatogram.

[1]

ii)

Identify the number of compounds present in this mixture and explain how to identify the most polar compound present.

[2]

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1b

6 marks

Two of the compounds in the organic mixture are hydrocarbons with similar retention times.

The mass spectra of the two compounds revealed that they have the same molecular formula but with subtle differences indicating structural isomerism is present.

The mass spectrum of one of the isomers is shown in Fig. 1.2.

Both isomers are tested with bromine water, which remains orange.

Fig. 1.2

i)

Identify the molar mass and hence the molecular formula of the isomers.

molar mass ................................................................................

molecular formula ................................................................................

[2]

ii)

Identify the fragments responsible for the following signals.

m / e = 29 ................................................................................

m / e = 43 ................................................................................

m / e = 57 ................................................................................

[3]

iii)

Suggest the most likely structure of the isomer responsible for this spectrum.

[1]

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1c3 marks

There is a small, additional peak on the far right of the mass spectrum.

i)

Explain the presence of the small peak at m / e = 87.

[1]

ii)

Suggest the type of molecules for which this would become more pronounced. Explain your answer.

[2]

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1d4 marks

One other isomer present in the original mixture was 2,3-dimethylbutane.

i)

Suggest one way in which the mass spectrum of 2,3-dimethylbutane will differ from Fig. 1.2 in part (b).

[1]

ii)

Suggest an alternative spectroscopic technique for distinguishing between 2,3-dimethylbutane and your answer to (b).

[1]

iii)

Predict which of the two isomers would have the longest retention time. Explain your answer.

[2]

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Gas/Liquid Chromatography (CIE A Level Chemistry)

Exam Questions