Aldehydes, Ketones & Carboxylic Acids

14 NEET-UG practice questions on Aldehydes, Ketones & Carboxylic Acids, part of Chemistry. The first 14 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A compound X, C₅H₁₀O, gives an orange precipitate with 2,4-DNP reagent and no silver mirror with Tollens' reagent. It gives a yellow precipitate with I₂ and NaOH. Clemmensen reduction of X gives n-pentane. Identify X.
1. APentan-3-one
2. BPentan-2-one
3. CPentanal
4. D3-Methylbutan-2-one
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Answer: B · Pentan-2-one
The 2,4-DNP result shows a carbonyl group and the negative Tollens' test rules out an aldehyde. The iodoform test requires a CH₃CO- group. A straight-chain pentane on reduction rules out branching, which leaves CH₃COCH₂CH₂CH₃.
- A: This has no CH₃CO- group, so it would not give the iodoform test.
- C: This aldehyde would give a silver mirror.
- D: This methyl ketone is branched, so reduction would give 2-methylbutane.
Remember this
Combine the tests: 2,4-DNP for C=O, Tollens' for aldehyde, iodoform for methyl ketone, and Clemmensen for the carbon skeleton.
Question 2 · Medium
Arrange these acids in increasing order of acid strength. A. HCOOH B. FCH₂COOH C. CH₃COOH D. ClCH₂COOH
1. AA, C, D, B
2. BC, A, B, D
3. CC, D, A, B
4. DC, A, D, B
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Answer: D · C, A, D, B
The pKa values are about 4.76 for CH₃COOH, 3.75 for HCOOH, 2.86 for ClCH₂COOH and 2.66 for FCH₂COOH. The -I effect of halogen stabilises the carboxylate, F more than Cl; the +I methyl destabilises it.
- A: This puts methanoic acid below ethanoic acid, ignoring the +I effect of methyl.
- B: This ranks Cl above F, though fluorine has the stronger -I effect.
- C: This places chloroacetic acid below methanoic acid, underrating the -I effect.
Remember this
Electron-withdrawing groups strengthen a carboxylic acid; fluorine acts more strongly than chlorine.
Question 3 · Easy
Which of these compounds gives a silver mirror when warmed with Tollens' reagent?
1. APropanal
2. BPropanoic acid
3. CPropanone
4. DPropan-2-ol
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Answer: A · Propanal
Tollens' reagent is a mild oxidising agent that oxidises aldehydes to carboxylate ions, and is itself reduced to metallic silver. Ketones do not respond under these conditions.
- B: This simple carboxylic acid has no aldehyde group.
- C: A ketone is not oxidised by this mild reagent.
- D: A secondary alcohol is not oxidised by Tollens' reagent.
Remember this
Tollens' test separates aldehydes from ketones, because only the aldehyde is easily oxidised.
Question 4 · Easy
Rosenmund reduction converts an acyl chloride into an aldehyde using hydrogen over which catalyst?
1. AZn-Hg with conc. HCl
2. BSnCl₂ with HCl
3. CLiAlH₄
4. DPd on BaSO₄
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Answer: D · Pd on BaSO₄
Partly poisoned palladium on barium sulphate stops the reduction at the aldehyde stage.
- A: This is the Clemmensen reagent, which takes C=O down to CH₂.
- B: This is the reagent of the Stephen reaction, which starts from a nitrile.
- C: This is a strong reducing agent that goes on to the alcohol and is not a catalyst for H₂.
Remember this
Rosenmund uses H₂ over Pd-BaSO₄ on acyl chlorides; Stephen uses SnCl₂/HCl on nitriles.
Question 5 · Medium
Propanal is warmed with dilute NaOH and the product is then heated. Which compound is finally obtained?
1. A3-Hydroxy-2-methylpentanal
2. B2-Methylpent-3-enal
3. C2-Methylpent-2-enal
4. DHex-2-enal
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Answer: C · 2-Methylpent-2-enal
The α-carbon of one propanal (CH₂) attacks the C=O of another, giving CH₃CH₂CH(OH)CH(CH₃)CHO. Heating removes water across the α and β carbons to give CH₃CH₂CH=C(CH₃)CHO.
- A: This is the aldol stage before heating removes water.
- B: This places the double bond out of conjugation with the carbonyl.
- D: This forms the new bond at the terminal CH₃, which is not the α-carbon.
Remember this
In aldol condensation the α-carbon forms the new bond and the C=C ends up conjugated with the C=O.
Question 6 · Medium
Match List-I with List-II. List-I (Named reaction) A. Clemmensen reduction B. Wolff-Kishner reduction C. Etard reaction D. Hell-Volhard-Zelinsky reaction List-II (Reagent) I. Br₂ with red phosphorus II. NH₂NH₂, then KOH in ethylene glycol III. Zn-Hg with conc. HCl IV. CrO₂Cl₂ in CS₂, then H₃O⁺
1. AA-II, B-III, C-IV, D-I
2. BA-III, B-II, C-I, D-IV
3. CA-II, B-III, C-I, D-IV
4. DA-III, B-II, C-IV, D-I
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Question 7 · Medium
A sample of 4.4 g of ethanal is completely oxidised by excess Tollens' reagent. Find the mass of silver deposited. (C = 12, H = 1, O = 16, Ag = 108)
1. A10.8 g
2. B21.6 g
3. C43.2 g
4. D32.4 g
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Question 8 · Hard
Follow this sequence. CH₃COOH + SOCl₂ → P P + H₂, Pd-BaSO₄ → Q Q + dil. NaOH, then heat → R What is R?
1. APropenal
2. B3-Hydroxybutanal
3. CButanal
4. DBut-2-enal
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Question 9 · Medium
Given below are two statements: Statement I: Propanone is more reactive than propanal towards nucleophilic addition. Statement II: A little base speeds up the addition of HCN to carbonyl compounds because it generates the stronger nucleophile CN⁻. Choose the correct answer.
1. AStatement I is correct but Statement II is incorrect
2. BBoth Statement I and Statement II are correct
3. CStatement I is incorrect but Statement II is correct
4. DBoth Statement I and Statement II are incorrect
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Question 10 · Medium
A mixture of benzaldehyde and methanal is treated with concentrated NaOH. Which are the main products of this crossed Cannizzaro reaction?
1. ASodium benzoate and methanol
2. BBenzyl alcohol and sodium methanoate
3. CBenzyl alcohol and sodium benzoate
4. DMethanol and sodium methanoate
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Question 11 · Medium
Propanone, 5.8 g, undergoes complete iodoform reaction with I₂ and NaOH. What mass of iodoform is obtained? (C = 12, H = 1, O = 16, I = 127)
1. A78.8 g
2. B14.2 g
3. C39.4 g
4. D19.7 g
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Question 12 · Hard
Propanal is treated as shown in the figure. Name the main product P.
Figure: MedExams
1. A2-Methylpent-2-enal
2. B2-Methylpent-3-enal
3. CHex-2-enal
4. D3-Hydroxy-2-methylpentanal
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Question 13 · Medium
Which of the compounds drawn undergo the Cannizzaro reaction with concentrated alkali but do NOT undergo aldol condensation with dilute alkali?
Figure: MedExams
1. AA and D only
2. BC only
3. CB and C only
4. DB, C and D only
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Question 14 · Easy
Arrange the carbonyl compounds drawn in order of increasing reactivity towards HCN. A. Structure A B. Structure B C. Structure C D. Structure D
Figure: MedExams
1. AA, C, D, B
2. BC, D, A, B
3. CB, D, A, C
4. DC, A, D, B
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Aldehydes, Ketones & Carboxylic Acids

A compound X, C₅H₁₀O, gives an orange precipitate with 2,4-DNP reagent and no silver mirror with Tollens' reagent. It gives a yellow precipitate with I₂ and NaOH. Clemmensen reduction of X gives n-pentane. Identify X.

Arrange these acids in increasing order of acid strength. A. HCOOH B. FCH₂COOH C. CH₃COOH D. ClCH₂COOH

Which of these compounds gives a silver mirror when warmed with Tollens' reagent?

Rosenmund reduction converts an acyl chloride into an aldehyde using hydrogen over which catalyst?

Propanal is warmed with dilute NaOH and the product is then heated. Which compound is finally obtained?

A sample of 4.4 g of ethanal is completely oxidised by excess Tollens' reagent. Find the mass of silver deposited. (C = 12, H = 1, O = 16, Ag = 108)

Follow this sequence. CH₃COOH + SOCl₂ → P P + H₂, Pd-BaSO₄ → Q Q + dil. NaOH, then heat → R What is R?

Given below are two statements: Statement I: Propanone is more reactive than propanal towards nucleophilic addition. Statement II: A little base speeds up the addition of HCN to carbonyl compounds because it generates the stronger nucleophile CN⁻. Choose the correct answer.

A mixture of benzaldehyde and methanal is treated with concentrated NaOH. Which are the main products of this crossed Cannizzaro reaction?

Propanone, 5.8 g, undergoes complete iodoform reaction with I₂ and NaOH. What mass of iodoform is obtained? (C = 12, H = 1, O = 16, I = 127)

Propanal is treated as shown in the figure. Name the main product P.

Which of the compounds drawn undergo the Cannizzaro reaction with concentrated alkali but do NOT undergo aldol condensation with dilute alkali?

Arrange the carbonyl compounds drawn in order of increasing reactivity towards HCN. A. Structure A B. Structure B C. Structure C D. Structure D