AS Level Chemistry chapter 17: Carbonyl compounds MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

24 exam-style questions on Carbonyl compounds, 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.

24 questions · 1 topics · 10 per test

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What chapter 17 covers

Ten Carbonyl compounds questions with answers

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

1. Which pair of compounds can be told apart using 2,4-dinitrophenylhydrazine (2,4-DNPH) alone?

  1. A
    propanal and propanone
  2. B
    ethanal and butanone
  3. C
    propanal and butanal
  4. D
    propanone and propan-2-ol
Show answer

Answer: D. 2,4-DNPH gives an orange precipitate with any aldehyde or ketone. Propanone reacts and propan-2-ol, an alcohol, does not. In the other pairs both compounds are carbonyls, so both give the precipitate.

2. Why is a little KCN added when HCN reacts with a carbonyl compound?

  1. A
    HCN is a strong acid, and KCN neutralises it.
  2. B
    KCN supplies K+ ions that attack the carbonyl oxygen.
  3. C
    HCN is a weak acid, so it supplies few CN− ions; KCN provides them, and CN− is regenerated.
  4. D
    KCN removes the water formed in the reaction.
Show answer

Answer: C. HCN is only slightly ionised, so there is too little CN− nucleophile. KCN is fully ionic and supplies it; the CN− is re-formed when the alkoxide ion takes H+ from HCN, so it acts as a catalyst. No water is formed in this addition.

3. Propan-2-ol is oxidised to propanone by acidified potassium dichromate(VI). What happens to the chromium?

  1. A
    It is reduced from +6 to +3.
  2. B
    It is oxidised from +3 to +6.
  3. C
    It is reduced from +7 to +2.
  4. D
    It is reduced from +6 to +2.
Show answer

Answer: A. In Cr2O72−, 2x + 7(−2) = −2, so x = +6. It is reduced to green Cr3+. +7 to +2 is the change for manganese in acidified MnO4−.

4. Which compound gives an orange precipitate with 2,4-dinitrophenylhydrazine?

  1. A
    ethanoic acid
  2. B
    ethyl ethanoate
  3. C
    propanone
  4. D
    ethanol
Show answer

Answer: C. 2,4-DNPH reacts with the C=O group of aldehydes and ketones only. Carboxylic acids and esters also contain C=O, but attached to oxygen, and they do not react.

5. Which alcohol is oxidised by acidified potassium dichromate(VI) to give butanone, CH3COCH2CH3?

  1. A
    butan-1-ol
  2. B
    2-methylpropan-2-ol
  3. C
    2-methylpropan-1-ol
  4. D
    butan-2-ol
Show answer

Answer: D. Ketones come from secondary alcohols, and the carbon skeleton is unchanged, so the OH must be on C2 of an unbranched four-carbon chain. Butan-1-ol gives butanal, and the tertiary alcohol is not oxidised.

6. Which aldehyde gives a yellow precipitate when warmed with alkaline aqueous iodine?

  1. A
    methanal
  2. B
    propanal
  3. C
    butanal
  4. D
    ethanal
Show answer

Answer: D. The test needs a CH3CO– group. Ethanal, CH3CHO, is the only aldehyde with one (R = H). Propanal and butanal have the C=O next to a CH2, and methanal has no carbon besides the carbonyl carbon.

7. Why are aldehydes oxidised by Tollens’ reagent while ketones are not?

  1. A
    Ketones have no oxygen atom that can be oxidised.
  2. B
    Ketones are more polar than aldehydes.
  3. C
    Aldehydes have a hydrogen atom on the carbonyl carbon; oxidising a ketone would need a C–C bond to break.
  4. D
    Aldehydes have a lower boiling point than ketones.
Show answer

Answer: C. An aldehyde, RCHO, is oxidised to RCOOH by turning the C–H on the carbonyl carbon into C–OH. A ketone has two carbons bonded to the carbonyl carbon, and a mild oxidising agent cannot break a C–C bond. Polarity and boiling point do not decide this.

8. Compound Y, C4H8O, gives an orange precipitate with 2,4-DNPH, no change with Fehling’s solution, and a yellow precipitate with alkaline aqueous iodine. What is Y?

  1. A
    butanal
  2. B
    2-methylpropanal
  3. C
    butan-2-ol
  4. D
    butanone
Show answer

Answer: D. The 2,4-DNPH result shows C=O; no reaction with Fehling’s means a ketone, not an aldehyde; and the iodoform result shows a CH3CO– group. Butanone, CH3COCH2CH3, fits all three. Butan-2-ol also gives the iodoform test but is not a carbonyl.

9. Compound X gives an orange precipitate with 2,4-DNPH and a silver mirror with Tollens' reagent. What is X?

  1. A
    a ketone
  2. B
    an aldehyde
  3. C
    a carboxylic acid
  4. D
    an ester
Show answer

Answer: B. The 2,4-DNPH result shows X is an aldehyde or ketone. Only aldehydes are easily oxidised, so only they reduce Tollens' reagent to a silver mirror; ketones give no reaction.

10. 2.20 g of ethanal is converted into 2-hydroxypropanenitrile, CH3CH(OH)CN, with a 60.0% yield. What mass of product is obtained?

  1. A
    1.32 g
  2. B
    2.13 g
  3. C
    3.55 g
  4. D
    5.92 g
Show answer

Answer: B. n(CH3CHO) = 2.20 ÷ 44.0 = 0.0500 mol. 0.0500 × 0.600 × 71.0 = 2.13 g. 3.55 g is the 100% figure, and 1.32 g is 60% of the ethanal mass.

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How many Carbonyl compounds MCQs are there?

24, each with the answer and a short explanation, across 1 topics: Aldehydes and ketones. Every chapter test draws ten of them, so you can take it many times.

Is the AS Level Chemistry chapter 17 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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