11 mark
TLC stands for
Travelling liquid chromatograph
Transitioning liquid chromatography
Transition layer chromatography
Thin-layer chromatography
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Chromatography (A-level only) (AQA A Level Chemistry)
Exam Questions
2 hours30 questions
21 mark
In thin-layer chromatography, which of the following can not be used to “locate” spots for colourless compounds?
Iodine vapour
Methyl orange
Ninhydrin
Ultraviolet light
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31 mark
A suitable carrier gas for use in gas-liquid chromatography is
Carbon dioxide
Chlorine
Nitrogen
Oxygen
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41 mark
A chromatogram showing the separation of a mixture of amino acids is shown.
|
A = Lysine |
B = Serine |
C = Histidine |
|
D = Tyrosine |
E = Isoleucine |
F = Methionine |
Which amino acid is the most soluble?
Isoleucine
Lysine
Methionine
Tyrosine
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51 mark
In chromatography, which of the following can be the mobile phase?
Liquid only
Liquid or gas
Solid or liquid
Gas only
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11 mark
A chromatogram of two compounds, A and B, is shown.
The Rf value of compound B is
0.21
0.44
0.65
1.54
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21 mark
The distance that an individual amino acid moves on a chromatogram depends on
The intermolecular forces between the amino acid and the stationary phase
The intermolecular forces between the amino acid and both the mobile and stationary phases
The intermolecular forces between the solvent and the stationary phase
The intermolecular forces between the solvent and both the mobile and stationary phases
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31 mark
In gas-liquid chromatography, gaseous samples pass through a long tube containing a liquid stationary phase.
The mixtures in the samples are separated into their components due to their
Force of attraction to the liquid
Force of attraction to the solid
Relative molecular mass
Volatility
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41 mark
Which of the following do components with a high Rf value have a greater affinity for?
No phase
The mobile phase
The stationary phase
The latent phase
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51 mark
Which of the following statements are correct for gas-liquid chromatography?
|
|
Components can be identified by their retention time |
The relative peak area gives the proportion of each component |
Calibration curves are used to compare component concentrations |
|
A |
✓ |
X |
X |
|
B |
✓ |
X |
✓ |
|
C |
✓ |
✓ |
X |
|
D |
✓ |
✓ |
✓ |
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11 mark
A tripeptide was hydrolysed and then analysed using thin-layer chromatography.
|
A = Lysine |
B = Serine |
C = Histidine |
D = Tyrosine |
|
E = Isoleucine |
F = Methionine |
G = Proline |
H = Hydrolysed tripeptide |
Using the information, which conclusion is correct?
The tripeptide is ser-tyr-met
The tripeptide contains mostly serine
The TLC needs to be run again using a different solvent
The tripeptide contains serine, tyrosine and methionine
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21 mark
A sample of cyclohexene contaminated with cyclohexanol is separated by column chromatography.
Hexane is used as the mobile phase and silica gel as the stationary phase.
Which statement correctly explains why cyclohexene has a shorter retention time than cyclohexanol?
Cyclohexene and cyclohexanol have different polarities
Cyclohexene is polar due to the C=C
Cyclohexanol is held in the mobile phase for longer
Cyclohexanol can form hydrogen bonds with the silica gel
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31 mark
The dipeptide cysteine-serine (cys-ser) and the dipeptide serine-cysteine (ser-cys) are shown.
Gas chromatography followed by mass spectrometry (GC-MS) is used to analyse a mixture of the two dipeptides.
Which statement about the analysis of the two dipeptides is correct?
Gas chromatography is unable to separate the two dipeptides
Cys-ser will have a greater retention time than ser-cys
Mass spectrometry is unable to distinguish between the dipeptides
The two dipeptides have the same relative affinity for the mobile and stationary phases
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41 mark
A student spotted samples of 1,2-dinitrobenzene, 1,3-dinitrobenzene and 1,4-dinitrobenzene on a silica gel TLC plate.
The solvent that the student used to run the TLC experiment was hexane.
The student calculated the Rf values for 1,2-dinitrobenzene and 1,4-dinitrobenzene.
|
Compound |
Rf value |
|
1,2-dinitrobenzene |
0.36 |
|
1,3-dinitrobenzene |
|
|
1,4-dinitrobenzene |
0.74 |
What could the Rf value for 1,3-dinitrobenzene be?
0.80
0.55
0.45
0.30
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51 mark
Zineb is a chemical that is used in agriculture as a fungicide. It is less toxic than other fungicides containing copper(II) compounds and it has a low solubility in water.
Recently, Zineb has been discontinued in many countries as one of its breakdown products is the highly water soluble compound ethylene thiourea (ETU).
ETU has been found to be carcinogenic, mutagenic and reproductively toxic.
Chromatography can be used to detect small quantities of ETU in Zineb.
Which statement about the analysis of ETU and Zineb is correct?
Gas-liquid chromatography is the most appropriate method of chromatography to separate ETU and Zineb
With a silica stationary phase and a water mobile phase, ETU has a higher Rf value than Zineb
With a silica stationary phase and a water mobile phase, ETU has a higher retention time than Zineb
Zineb has a greater affinity for the water mobile phase than ETU
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