Aldehydes, Ketones and Carboxylic Acids: Class 12 Important Questions with Answers

Practice set: test yourself

Try every question before looking at the answers below. 64 or more out of 80 means you are ready for the board.

C. Very short answer (1 mark each)

1. IUPAC name of CH₃COCH₂CH₃.
2. Write the Stephen reaction product of CH₃CN.
3. Name the reagent for toluene → benzaldehyde.
4. Give an aldehyde with no α-H.
5. Product of 2CH₃CHO + dil NaOH.
6. Reagent: acid → acid chloride.
7. Which is more acidic: FCH₂COOH or ClCH₂COOH?
8. Product of benzoic acid + NaOH/CaO.
9. What is a cyanohydrin?
10. Give one use of formalin.

D. Short answer I (2 marks each)

1. Distinguish propanal and propanone by two tests.
2. Write the Cannizzaro reaction of HCHO.
3. Why are α-hydrogens acidic?
4. Arrange by reactivity towards HCN: acetone, ethanal, methanal, butanone.
5. Write the Clemmensen reduction of acetophenone.
6. Why is benzoic acid stronger than acetic acid?
7. Write the HVZ reaction of propanoic acid.
8. How is acetone obtained from CH₃CN?

Rough work

E. Short answer II (3 marks each)

1. Explain the mechanism of nucleophilic addition to the carbonyl group.
2. Write the aldol condensation of ethanal and of propanone.
3. Convert: (a) benzene → acetophenone (b) benzoic acid → benzaldehyde (c) ethanal → but-2-enal.
4. Arrange in increasing acid strength with reasons: CH₃COOH, Cl₂CHCOOH, ClCH₂COOH, CCl₃COOH.
5. Explain why carboxylic acids are stronger than phenols.
6. Give the preparation of carboxylic acids from (a) Grignard reagents (b) nitriles (c) alkylbenzenes.

F. Long answer (5 marks each)

1. A compound C₄H₈O gives a 2,4-DNP derivative and a positive iodoform test but no Tollens' test. (a) Identify it. (b) Write its reactions with I₂/NaOH, NaBH₄ and Zn–Hg/HCl. (c) Name an isomer that gives Tollens' test.
2. (a) Write the Rosenmund, Etard and Stephen reactions. (b) Why do aldehydes give Tollens' test but ketones do not? (c) Give a test for HCOOH that CH₃COOH does not give.

G. HOTS (higher-order thinking)

1. Why does HCOOH reduce Tollens' reagent though it is an acid?
2. Why does 2,2,6-trimethylcyclohexanone not form a cyanohydrin easily?
3. Why is the pH kept near 3.5 in forming oximes and semicarbazones?
4. Why is the b.p. of acetic acid higher than that of ethanol?

20 MCQs

1. Most reactive towards HCN
   (a) acetone (b) acetophenone (c) methanal (d) benzophenone
2. Undergoes Cannizzaro
   (a) C₆H₅CHO (b) CH₃CHO (c) CH₃COCH₃ (d) CH₃CH₂CHO
3. Clemmensen reagent
   (a) NH₂NH₂/KOH (b) H₂/Pd–BaSO₄ (c) LiAlH₄ (d) Zn–Hg/conc HCl
4. Gives iodoform
   (a) propanal (b) acetophenone (c) benzaldehyde (d) pentan-3-one
5. Strongest acid
   (a) CH₃COOH (b) CF₃COOH (c) HCOOH (d) C₆H₅COOH
6. Toluene → benzaldehyde
   (a) Rosenmund (b) Cannizzaro (c) Stephen (d) Etard
7. RCOOH + X₂/red P
   (a) HVZ (b) decarboxylation (c) esterification (d) Kolbe
8. Aldol product of ethanal
   (a) but-2-enal (b) butanal (c) 3-hydroxybutanal (d) ethanol
9. Fehling's test is negative for
   (a) ethanal (b) methanal (c) propanal (d) benzaldehyde
10. 2C₆H₅COCl + (CH₃)₂Cd
    (a) benzophenone (b) acetophenone (c) benzaldehyde (d) toluene
11. Nitrile → aldehyde
    (a) LiAlH₄ (b) NaBH₄ (c) DIBAL-H (d) KMnO₄
12. NaHCO₃ effervescence with
    (a) benzoic acid (b) phenol (c) ethanol (d) benzaldehyde
13. Carboxylic acid reduced by
    (a) NaBH₄ (b) LiAlH₄ (c) Zn–Hg (d) Sn/HCl
14. meta product of C₆H₅COOH + HNO₃
    (a) o-nitrobenzoic (b) p-nitrobenzoic (c) m-nitrobenzoic (d) nitrobenzene
15. CH₃COOH + P₂O₅
    (a) CH₃COCl (b) CH₄ (c) CH₃CHO (d) (CH₃CO)₂O
16. Silver mirror with
    (a) propanal (b) propanone (c) acetophenone (d) benzophenone
17. Phthalic acid + NH₃, strong heat
    (a) phthalimide (b) aniline (c) benzamide (d) benzonitrile
18. Higher b.p. than CH₃CH₂OH
    (a) CH₃CHO (b) C₃H₈ (c) CH₃OCH₃ (d) CH₃COOH
19. Semicarbazone formation needs
    (a) strong acid (b) weakly acidic pH (c) strong base (d) light
20. Decarboxylation reagent
    (a) H₂SO₄ (b) Na/ether (c) NaOH + CaO (d) Br₂

1 (c) · 2 (a) · 3 (d) · 4 (b) · 5 (b) · 6 (d) · 7 (a) · 8 (c) · 9 (d) · 10 (b) · 11 (c) · 12 (a) · 13 (b) · 14 (c) · 15 (d) · 16 (a) · 17 (a) · 18 (d) · 19 (b) · 20 (c)

Assertion–Reason (6)

(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

1. A: Aldehydes are more reactive than ketones. R: Ketones have two electron-releasing groups and more steric hindrance.
2. A: Benzaldehyde undergoes Cannizzaro reaction. R: It has no α-hydrogen.
3. A: Formic acid is stronger than acetic acid. R: The methyl group has –I effect.
4. A: Carboxylic acids do not give 2,4-DNP test. R: The carboxyl carbon is less electrophilic due to resonance.
5. A: Acetone gives iodoform test. R: Acetone has a CH₃CO– group.
6. A: Ethanal is more reactive than methanal towards HCN. R: CH₃ is electron-releasing.

Key: 1 (a) · 2 (a) · 3 (c) · 4 (a) · 5 (a) · 6 (d)

Answers to the practice set