AS Level Chemistry chapter 22: Analytical techniques MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

46 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.

46 questions · 2 topics · 10 per test

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What chapter 22 covers

Ten Analytical techniques questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. In the mass spectrum of a hydrocarbon the M peak has a relative height of 20.0 and the [M + 1] peak a relative height of 1.32. How many carbon atoms are in each molecule?

  1. A
    5
  2. B
    6
  3. C
    7
  4. D
    8
Show answer

Answer: B. n = (100 × 1.32) ÷ (1.1 × 20.0) = 6.0. Leaving out the 1.1 gives 6.6, which rounds wrongly to 7.

2. Gallium has two isotopes: 69Ga (60.1%) and 71Ga (39.9%). What is the relative atomic mass of gallium?

  1. A
    69.0
  2. B
    69.8
  3. C
    70.0
  4. D
    70.2
Show answer

Answer: B. Ar = (69 × 60.1 + 71 × 39.9) ÷ 100 = 69.8. 70.2 swaps the abundances; 70.0 is a simple average that ignores abundance.

3. Which compound shows absorptions at 1040–1300 cm−1 and 1670–1740 cm−1 and a broad absorption at 2500–3000 cm−1?

  1. A
    methyl ethanoate
  2. B
    propan-1-ol
  3. C
    propanoic acid
  4. D
    propanal
Show answer

Answer: C. Propanoic acid has C–O (1040–1300), C=O (1670–1740) and the acid O–H (2500–3000). Methyl ethanoate has C–O and C=O but no O–H; propan-1-ol has no C=O; propanal has no C–O or O–H.

4. A compound contains one chlorine atom and one bromine atom. Chlorine is 35Cl : 37Cl = 3 : 1 and bromine is 79Br : 81Br = 1 : 1. What is the ratio of the heights of the M, [M + 2] and [M + 4] peaks?

  1. A
    1 : 2 : 1
  2. B
    3 : 1 : 1
  3. C
    3 : 4 : 1
  4. D
    9 : 6 : 1
Show answer

Answer: C. Combine (3 : 1) for Cl with (1 : 1) for Br: M = 3 × 1 = 3; [M + 2] = 3 × 1 + 1 × 1 = 4; [M + 4] = 1 × 1 = 1. 1 : 2 : 1 is the pattern for two Br atoms and 9 : 6 : 1 for two Cl atoms.

5. Which set of infrared absorptions would be seen for 2-hydroxypropanenitrile, CH3CH(OH)CN? Use these infrared absorption ranges: C–O 1040–1300; C=C 1500–1680; C=O 1670–1740; C≡N 2200–2250; C–H 2850–2950; O–H (acids) 2500–3000; O–H (alcohols) 3200–3600 cm−1.

  1. A
    1670–1740 and 3200–3600 cm−1, but none at 2200–2250 cm−1
  2. B
    2200–2250 and 2500–3000 cm−1, but none at 3200–3600 cm−1
  3. C
    1670–1740 and 2200–2250 cm−1, but none at 3200–3600 cm−1
  4. D
    2200–2250 and 3200–3600 cm−1, but none at 1670–1740 cm−1
Show answer

Answer: D. The molecule has C≡N (2200–2250) and an alcohol O–H (3200–3600); it has no C=O. The 2500–3000 range is for the O–H of carboxylic acids.

6. Which pair of compounds cannot be told apart by the functional-group absorptions in their infrared spectra?

  1. A
    propanal and propan-1-ol
  2. B
    propan-1-ol and propan-2-ol
  3. C
    propanoic acid and propan-1-ol
  4. D
    propene and propane
Show answer

Answer: B. Propan-1-ol and propan-2-ol have the same bonds (O–H, C–O, C–H), so their functional-group absorptions match. Each other pair differs: C=O, the acid O–H range, or C=C.

7. The molecular ion peak of an organic compound is at m/e = 60. Which compound could it be?

  1. A
    propanal
  2. B
    propan-1-ol
  3. C
    butan-1-ol
  4. D
    ethanal
Show answer

Answer: B. The molecular ion peak gives Mr. Propan-1-ol, C3H7OH: 3 × 12.0 + 8 × 1.0 + 16.0 = 60.0. Propanal is 58, butan-1-ol 74 and ethanal 44.

8. The mass spectrum of a pure sample of magnesium shows a small peak at m/e 12. What is the best explanation?

  1. A
    12C+ ions from carbon impurity
  2. B
    24MgH+ ions
  3. C
    24Mg+ ions split in half
  4. D
    24Mg2+ ions
Show answer

Answer: D. m/e is mass ÷ charge, so a doubly charged 24Mg2+ ion appears at 24 ÷ 2 = 12. The sample is pure, so carbon is not the answer, and MgH+ would appear at 25.

9. Pentan-2-one, CH3COCH2CH2CH3, and pentan-3-one, CH3CH2COCH2CH3, both have Mr = 86. Breaking one C–C bond in the molecular ion, which m/e value is expected only for pentan-2-one?

  1. A
    15
  2. B
    29
  3. C
    57
  4. D
    43
Show answer

Answer: D. Pentan-2-one can give CH3CO+ or C3H7+, both at 43. Pentan-3-one gives C2H5+ (29), C2H5CO+ (57) and CH3+ (15), and none of its single-bond fragments has mass 43; 15, 29 and 57 can come from both ketones.

10. The mass spectrum of magnesium has peaks at m/e 24 (79.0%), 25 (10.0%) and 26 (11.0%). What is the relative atomic mass of magnesium?

  1. A
    24.0
  2. B
    24.1
  3. C
    24.3
  4. D
    25.0
Show answer

Answer: C. Ar = (24 × 79.0 + 25 × 10.0 + 26 × 11.0) ÷ 100 = 24.32 = 24.3. Leaving out the m/e 26 isotope gives 24.1; 25.0 is the unweighted mean.

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Analytical techniques: questions students ask

How many Analytical techniques MCQs are there?

46, each with the answer and a short explanation, across 2 topics: Infrared spectroscopy, Mass spectrometry. Every chapter test draws ten of them, so you can take it many times.

Is the AS Level Chemistry chapter 22 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.

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