AQA A-Level Chemistry Paper 3, June 2022: Question 31

1 mark · Easy difficulty · Multiple Choice

Identify which pair of reagents does not produce ethanol.

Practise this question

Question

Question 31 asks: 'Which pair of reagents does not produce ethanol?' with 1 mark. Four multiple-choice options are given: A: CH3CH2Br and NaOH(aq), B: CH3COOCH3 and NaOH(aq), C: HCOOCH2CH3 and NaOH(aq), and D: CH3CHO and NaBH4(aq). Each option has a selection box beside it.
Question text

31 Which pair of reagents does not produce ethanol?

[1 mark]

A CH3CH2Br and NaOH(aq)

B CH3COOCH3 and NaOH(aq)

C HCOOCH2CH3 and NaOH(aq)

D CH3CHO and NaBH4(aq)

Mark scheme

Show the mark scheme Mark scheme for Question 31 indicates the correct answer is B (AO2) with 1 mark, corresponding to CH3COOCH3 and NaOH(aq).

31 B (AO2) 1 CH3COOCH3 and NaOH(aq)

How to answer it

Reactions Forming Ethanol & Ester Hydrolysis

📋 What this question tests

This multiple-choice question assesses your knowledge of organic functional group conversions that produce alcohols, specifically:

  • Nucleophilic substitution of halogenoalkanes with aqueous hydroxide ions.
  • Alkaline hydrolysis (saponification) of esters into a carboxylate salt and an alcohol.
  • Reduction of aldehydes using sodium borohydride (NaBH₄).
  • Differentiating between the acyl group and the alkoxy group in ester formulas.
Question 31

Identifying the Reaction that Does NOT Produce Ethanol

AQA A-Level Chemistry | Organic Synthesis & Functional Groups | 1 Mark

✅ Correct Answer

B: CH₃COOCH₃ and NaOH(aq)

Mark Scheme Breakdown:
• 1 Mark (AO2) for selecting option B.

Alkaline hydrolysis of methyl ethanoate ( CH₃COOCH₃ ) produces:
CH₃COONa (sodium ethanoate) + CH₃OH (methanol).
Because it produces methanol rather than ethanol, this is the correct choice for the reaction that does not yield ethanol.

💡 Reaction Breakdown for All Options

  • A: CH₃CH₂Br + NaOH(aq)
    Nucleophilic substitution of bromoethane:
    CH₃CH₂Br + OH⁻ → CH₃CH₂OH + Br⁻
    Result: Produces ethanol.
  • B: CH₃COOCH₃ + NaOH(aq)
    Base hydrolysis of methyl ethanoate:
    CH₃COOCH₃ + NaOH → CH₃COONa + CH₃OH
    Result: Produces methanol (NO ethanol).
  • C: HCOOCH₂CH₃ + NaOH(aq)
    Base hydrolysis of ethyl methanoate:
    HCOOCH₂CH₃ + NaOH → HCOONa + CH₃CH₂OH
    Result: Produces ethanol.
  • D: CH₃CHO + NaBH₄(aq)
    Nucleophilic addition / reduction of ethanal:
    CH₃CHO + 2[H] → CH₃CH₂OH
    Result: Produces ethanol.

🧠 Exam Technique: Ester Cleavage Rule

When an ester R–COO–R' hydrolyses:

  • The acyl part ( R–CO– ) comes from the parent carboxylic acid and forms the salt R–COO⁻ Na⁺ .
  • The alkoxy part ( –O–R' ) comes from the parent alcohol and forms the free alcohol R'–OH .

To form ethanol ( CH₃CH₂OH ), the alkyl group attached directly to the oxygen ( R' ) must be an ethyl group ( –CH₂CH₃ ), as seen in Option C, not a methyl group as in Option B.

❌ Common Student Traps

  • Missing the negative word: Overlooking the word "not" in the question stem is the #1 reason students lose this mark. Always circle "NOT" in multiple-choice questions.
  • Confusing the two ends of an ester: Seeing CH₃COO– in Option B and assuming the two carbons will yield ethanol. Remember, the acyl two-carbon chain ends up as the ethanoate salt, not the alcohol.
  • Confusing conditions for halogenoalkanes: Thinking Option A produces ethene. NaOH(aq) favours substitution to form alcohol; hot ethanolic KOH would cause elimination to form an alkene.

Topics

Organic Chemistry · 3.3.3 Halogenoalkanes · 3.3.5 Alcohols · 3.3.8 Aldehydes and Ketones · 3.3.9 Carboxylic Acids and Derivatives

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.