MDCAT Chemistry chapter 17: Chemistry · Aldehydes and ketones MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

40 exam-style questions on Chemistry · Aldehydes and ketones, 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.

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What chapter 17 covers

Ten Chemistry · Aldehydes and ketones questions with answers

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

1. Ethanal is warmed with excess methanol in the presence of dry HCl gas. The final organic product, an acetal, is

  1. A
    CH3CH(OH)OCH3
  2. B
    CH3COOCH3
  3. C
    CH3CH(OCH3)2
  4. D
    CH3CH2OCH3
Show answer

Answer: C. One methanol molecule adds across C=O to give the hemiacetal CH3CH(OH)OCH3; with acid and excess methanol its –OH is then replaced by a second –OCH3, with loss of water. CH3COOCH3 is an ester, which would need a carboxylic acid.

2. Which structure is a hemiacetal?

  1. A
    CH3CH(OH)OC2H5
  2. B
    CH3CH(OC2H5)2
  3. C
    CH3CH(OH)CH2OCH3
  4. D
    CH3COOC2H5
Show answer

Answer: A. A hemiacetal has an –OH group and an –OR group on the same carbon; it forms when one alcohol molecule adds across the C=O of an aldehyde: CH3CHO + C2H5OH ⇌ CH3CH(OH)OC2H5. CH3CH(OC2H5)2 is the acetal, and in CH3CH(OH)CH2OCH3 the two oxygen atoms are on different carbons.

3. The common name β-methylbutyraldehyde corresponds to the IUPAC name

  1. A
    2-methylbutanal
  2. B
    3-methylpentanal
  3. C
    2-methylpropanal
  4. D
    3-methylbutanal
Show answer

Answer: D. Butyraldehyde is butanal, CH3CH2CH2CHO, and the β-carbon is the second carbon from –CHO, which is C-3 in IUPAC numbering, giving (CH3)2CHCH2CHO, 3-methylbutanal. Reading β as C-2 gives 2-methylbutanal, which is the α-compound.

4. Saturated aldehydes and ketones share the general formula CnH2nO. Which pair are functional group isomers of each other?

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

Answer: A. Propanal, CH3CH2CHO, and propanone, CH3COCH3, are both C3H6O but have different functional groups. Ethanal and propanal are homologues, propan-2-ol is C3H8O, and butanal and 2-methylpropanal are chain isomers.

5. In the common system of naming, which uses Greek letters for positions, ClCH2CH2CHO is called

  1. A
    α-chloropropionaldehyde
  2. B
    β-chloropropionaldehyde
  3. C
    γ-chloropropionaldehyde
  4. D
    β-chlorobutyraldehyde
Show answer

Answer: B. Greek letters start with α for the carbon next to the –CHO group, so the CH2Cl carbon, the second one along, is β. Its IUPAC name is 3-chloropropanal, because IUPAC numbering counts the –CHO carbon itself as C-1.

6. Clemmensen and Wolff–Kishner reductions both convert a C=O group into a CH2 group. They differ in that

  1. A
    Clemmensen uses hydrazine and KOH; Wolff–Kishner uses Zn(Hg) and conc. HCl
  2. B
    Clemmensen uses LiAlH4; Wolff–Kishner uses NaBH4
  3. C
    Clemmensen works only on aldehydes; Wolff–Kishner works only on ketones
  4. D
    Clemmensen uses Zn(Hg) and conc. HCl; Wolff–Kishner uses hydrazine and KOH
Show answer

Answer: D. Clemmensen reduction is carried out in acid, with amalgamated zinc and hydrochloric acid, whereas Wolff–Kishner reduction converts the carbonyl compound into its hydrazone with NH2NH2 and heats it with a strong base, releasing N2. Both work on aldehydes and ketones; LiAlH4 and NaBH4 stop at the alcohol.

7. A carbonyl compound C4H8O gives an orange precipitate with 2,4-DNPH but no silver mirror with Tollens' reagent. With sodium nitroprusside solution made alkaline with NaOH, it gives

  1. A
    no change, as only aldehydes react
  2. B
    a brick-red precipitate of Cu2O
  3. C
    a yellow precipitate of CHI3
  4. D
    a red colour, showing a ketone
Show answer

Answer: D. A carbonyl compound that does not reduce Tollens' reagent is a ketone, so this C4H8O is butanone, CH3COCH2CH3, and ketones give a red colour with alkaline sodium nitroprusside. The yellow CHI3 needs iodine and NaOH, and Cu2O comes from Fehling's solution with an aldehyde.

8. Which ketone is formed when dry calcium propanoate, (CH3CH2COO)2Ca, is heated strongly?

  1. A
    pentan-3-one
  2. B
    butanone
  3. C
    propanone
  4. D
    pentan-2-one
Show answer

Answer: A. The carbonyl carbon of one propanoate group ends up carrying the ethyl groups of both, giving CH3CH2COCH2CH3, while the other carboxylate carbon leaves as CaCO3. The ketone has 2 × 3 − 1 = 5 carbons, with the C=O in the middle.

9. Methanal, HCHO, has the same empirical formula as

  1. A
    ethanal, CH3CHO
  2. B
    methanoic acid, HCOOH
  3. C
    ethanoic acid, CH3COOH
  4. D
    ethane-1,2-diol, HOCH2CH2OH
Show answer

Answer: C. The empirical formula of methanal is CH2O, and ethanoic acid, C2H4O2, reduces to the same ratio, as does glucose. Ethanal is C2H4O, methanoic acid CH2O2 and ethane-1,2-diol C2H6O2, that is CH3O.

10. Which reagent gives a positive result with ethanal but not with benzaldehyde?

  1. A
    Tollens' reagent
  2. B
    2,4-dinitrophenylhydrazine
  3. C
    Fehling's solution
  4. D
    sodium hydrogensulphite
Show answer

Answer: C. Aliphatic aldehydes reduce the copper(II) complex in Fehling's solution to a red precipitate of Cu2O, but aromatic aldehydes such as benzaldehyde do not. Both aldehydes give a silver mirror with Tollens' reagent, a precipitate with 2,4-DNPH and an addition product with sodium hydrogensulphite.

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How many Chemistry · Aldehydes and ketones MCQs are there?

40, 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.

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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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