A Level Chemistry (A2) chapter 15: Analytical techniques MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
96 exam-style questions on Analytical techniques, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. The components of a mixture are colourless. How can their spots be located on an aluminium oxide TLC plate after it has been run?
A
by heating the plate until the solvent boils
B
by running the plate again in the same solvent
C
by measuring the solvent front more carefully
D
by viewing the plate under ultraviolet light or exposing it to iodine vapour
Show answer
Answer: D. Spots are made visible by UV light (on a fluorescent plate) or by a locating agent such as iodine vapour. The other actions do not reveal colourless compounds.
2. A compound C4H8O has three peaks in its carbon-13 NMR spectrum, one of them at δ 204. (Typical δ/ppm: alkyl C 0–50; C next to C=O 30–65; C–O 50–70; C=C 110–160; C=O in aldehydes and ketones 190–220) Which compound fits?
A
butanal, CH3CH2CH2CHO
B
butanone, CH3COCH2CH3
C
2-methylpropanal, (CH3)2CHCHO
D
but-3-en-2-ol, CH2=CHCH(OH)CH3
Show answer
Answer: C. The peak at δ 204 shows a C=O in an aldehyde or ketone. Butanal and butanone each have four different carbons; 2-methylpropanal has two equivalent CH3 groups, giving three peaks. But-3-en-2-ol has no C=O and four peaks.
3. Why is the baseline on a TLC plate drawn in pencil rather than in ink?
A
pencil lines are easier to see under ultraviolet light after development
B
ink reacts with the aluminium oxide stationary phase and blocks the spots
C
ink would dissolve in the solvent and move up the plate, giving extra spots
D
pencil graphite helps the solvent to rise up the plate more evenly
Show answer
Answer: C. Graphite is insoluble in the solvent and stays where it is drawn; the dyes in ink are soluble and would be separated along with the sample.
4. An unknown compound X gives a spot with the same Rf value as pure compound P when both are run on the same plate in hexane. Which further result gives the best extra evidence that X is P?
A
The spot of X is larger than the spot of P.
B
X and P also have the same Rf value when run in a solvent of different polarity.
C
The Rf value of X is measured to three decimal places.
D
X gives the same Rf value again in hexane on a longer plate.
Show answer
Answer: B. Different compounds can have the same Rf in one solvent by chance. Matching in a second, different solvent makes this much less likely. A longer plate in the same solvent repeats the same test, and spot size depends on how much was applied.
5. Which compound gives a proton NMR spectrum in which one peak disappears when the sample is shaken with D2O?
A
propanone
B
propan-1-ol
C
methyl ethanoate
D
1-chloropropane
Show answer
Answer: B. Only propan-1-ol has a proton on O (or N) that can exchange with deuterium. The others contain only C–H protons, which do not exchange with D2O.
6. In the proton NMR spectrum of 2,2-dimethylpropanal, (CH3)3CCHO, where does the peak for the aldehyde proton appear and what is its splitting? (Typical δ: alkyl H 0.9–1.7; H–C–C=O 2.0–2.7; aldehyde H 9.3–10.5)
A
about δ 9.5; singlet
B
about δ 9.5; multiplet
C
about δ 2.4; singlet
D
about δ 2.4; multiplet
Show answer
Answer: A. The aldehyde proton is strongly deshielded and appears at 9.3–10.5. The n + 1 rule counts only the H atoms on the adjacent carbon, and the carbon next to –CHO carries three CH3 groups but no H, so the peak is a singlet. The nine methyl protons are one carbon further away and do not split it.
7. For a given compound, which change would not change its Rf value?
A
changing the solvent from hexane to ethyl ethanoate
B
using silica instead of aluminium oxide as the stationary phase
C
using a longer plate with the same stationary phase and solvent
D
adding some ethanol to the hexane solvent
Show answer
Answer: C. Rf is a ratio of distances; on a longer plate both the spot and the front move further in the same proportion. Changing the solvent or the stationary phase changes how the compound is shared between the phases.
8. A mixture of pentane, hexane and heptane is analysed on a column with a non-polar stationary phase. In what order do the compounds reach the detector?
A
heptane first, then hexane, then pentane
B
hexane first, then pentane, then heptane
C
pentane first, then hexane, then heptane
D
all three at the same time, as they have the same functional group
Show answer
Answer: C. Larger alkanes have stronger instantaneous dipole–induced dipole forces with the non-polar stationary liquid (and higher boiling points), so they spend longer in the stationary phase and have longer retention times.
9. A mixture of methylbenzene, phenylmethanol (C6H5CH2OH) and benzoic acid is separated by TLC on an aluminium oxide plate using hexane as the solvent. Which compound has the highest Rf value?
A
methylbenzene
B
phenylmethanol
C
benzoic acid
D
all three have the same Rf value
Show answer
Answer: A. Aluminium oxide is a polar stationary phase and hexane a non-polar mobile phase. Non-polar methylbenzene is held least strongly by the stationary phase and is most soluble in hexane, so it travels furthest.
10. Which gas would be unsuitable as the carrier gas in gas/liquid chromatography, and why?
A
oxygen, because it could oxidise the sample or the hot stationary liquid
B
nitrogen, because it is too unreactive to carry the sample
C
helium, because its atoms are too small to carry the sample
D
argon, because noble gases dissolve in the stationary liquid
Show answer
Answer: A. The mobile phase must be an unreactive gas such as nitrogen, helium or argon. Oxygen would react with the organic sample or stationary phase in the heated column.
96, each with the answer and a short explanation, across 4 topics: Thin-layer chromatography, Gas / liquid chromatography, Carbon-13 NMR spectroscopy, Proton ( H) NMR spectroscopy. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Chemistry (A2) chapter 15 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
