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A Levels Chemistry (9701)•9701/12/O/N/20
Question 40 from 9701/12/O/N/20

Explanation

Oxidation of hydrocarbons to carboxylic acids

Steps:

  • Pentanoic acid is CH3(CH2)3COOH, a 5-carbon carboxylic acid formed by oxidation cleaving C-C bonds.
  • Evaluate A: Propan-1-ol (3 carbons) oxidizes to propanoic acid (3 carbons).
  • Evaluate B: Butan-2-one (4 carbons) with H2SO4 undergoes acid-catalyzed reactions but not full oxidation to pentanoic acid.
  • Evaluate C: Pentane (5 carbons) with hot concentrated H2SO4/KMnO4 oxidizes to pentanoic acid via cleavage.

Why C is correct:

  • Oxidative cleavage of pentane (C5H12) with H2SO4(aq) (implying KMnO4 conditions) breaks the chain to yield CH3(CH2)3COOH.

Why the others are wrong:

  • A: Yields propanoic acid (CH3CH2COOH), a 3-carbon acid, due to primary alcohol oxidation stopping at carboxylic acid.
  • B: Ketone hydration or no reaction; does not produce a 5-carbon carboxylic acid.
  • D: No reaction or information provided.

Final answer: C

Topic: Carboxylic acids and derivatives

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