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Oxidation of alcohols test answers and mark scheme for A Level chemistry (free PDF download)

The questions are on the oxidation of alcohols test. Take it under real conditions before reading the mark scheme.

Quick answer: Primary alcohols are oxidised to aldehydes and then carboxylic acids, secondary alcohols to ketones, and tertiary alcohols resist oxidation; acidified dichromate turns from orange to green. This mark scheme gives the model answers and the marks for the 8 questions of the Chemistry 11-12 test on oxidation of alcohols, from oxidising butan-2-ol to identify by tests, with the equivalent answers to accept.

Oxidation of alcohols test answers and mark scheme for A Level chemistry (free PDF download)

The answers include a mark scheme. Give full credit for correct reasoning even if the wording differs, but do not accept “clear” for colourless or a silver mirror for a ketone. Check units and significant figures in the calculation.

Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.3.5

Question 1 Oxidising butan-2-ol (3 marks)

  1. Secondary.
  2. Butanone.
  3. Orange to green.

Marking: 1 mark each.

Question 2 Reflux or distillation (2 marks)

  1. Distillation: propanal; reflux: propanoic acid.
  2. Propanal has no hydrogen bonding, so it boils at a lower temperature than the alcohol and escapes before further oxidation.

Marking: 1 for both names; 1 for the explanation.

Question 3 Tollens’ reagent (3 marks)

  1. Ethanal: a silver mirror forms. Propanone: no change.
  2. They are reduced to silver metal (Ag⁺ + e⁻ → Ag).

Marking: 1 for each observation; 1 for reduction.

Question 4 Propanone and HCN (3 marks)

  1. Nucleophilic addition.
  2. (CH₃)₂C(OH)CN, 2-hydroxy-2-methylpropanenitrile.
  3. It has two identical CH₃ groups, so there is no chiral centre.

Marking: 1 mark each.

Question 5 Yield calculation (3 marks)

  1. n = 4.60 / 46.0 = 0.100 mol; mass = 0.100 × 60.0 = 6.00 g.
  2. 0.80 × 6.00 = 4.80 g.

Marking: 1 for amount; 1 for mass; 1 for 4.80 g.

Question 6 Racemic product (2 marks)

  1. An equal mixture of two enantiomers.
  2. The planar C=O is attacked equally from each face by CN⁻.

Marking: 1 mark each.

Question 7 Boiling points (2 marks)

  1. Hydrogen bonding.
  2. Propanal has no O–H group, so only weaker dipole-dipole forces act between its molecules.

Marking: 1 mark each.

Question 8 Identify by tests (2 marks)

  1. Propanone.
  2. DNPH shows a carbonyl group; no reaction with Fehling’s solution shows it is a ketone, not an aldehyde.

Marking: 1 mark each.

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