OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2023: Question 14

1 mark · Medium difficulty · Multiple Choice

Identify which given compound(s) can be hydrolysed by aqueous acid to produce butanoic acid

Practise this question

Question

Multiple choice question 14 asks which of the three listed compounds is hydrolysed by HCl(aq) to produce butanoic acid. Compound 1 is CH3CH2CH2COOCH3, compound 2 is CH3CH2CH2CH2CN, and compound 3 is CH3CH2CH2CH2Cl. Four options A to D are provided: A is 1, 2 and 3; B is Only 1 and 2; C is Only 2 and 3; D is Only 1. A box for 'Your answer' is shown at the bottom.
Question text

14 Which compound(s) is/are hydrolysed by HCl(aq) to produce butanoic acid?

1 CH3CH2CH2COOCH3

2 CH3CH2CH2CH2CN

3 CH3CH2CH2CH2Cl

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

[1]

Mark scheme

Show the mark scheme Mark scheme for question 14 showing the correct answer is D, worth 1 mark.

14 D 1 AO1.2

How to answer it

Hydrolysis to Produce Butanoic Acid

What this question tests

This question assesses your knowledge of functional group chemistry, specifically the hydrolysis reactions of esters, nitriles, and halogenoalkanes under acidic conditions (HCl(aq)), with a strong focus on tracking carbon chain lengths to form carboxylic acids.

Question 14

Analysis of Compounds

✅ Correct Answer: D (Only 1)

Compound 1 is the only species that hydrolyses to form butanoic acid.

💡 Key Knowledge

  • Butanoic acid contains 4 carbon atoms in total ( CH₃CH₂CH₂COOH ).
  • Esters (Statement 1): CH₃CH₂CH₂COOCH₃ is methyl butanoate. Acid hydrolysis yields butanoic acid ( CH₃CH₂CH₂COOH ) and methanol. Total carbons in the acid chain = 4.
  • Nitriles (Statement 2): CH₃CH₂CH₂CH₂CN is pentanenitrile (5 carbons). Acid hydrolysis converts the -CN group into a carboxylic acid ( -COOH ), yielding pentanoic acid, not butanoic acid.
  • Halogenoalkanes (Statement 3): CH₃CH₂CH₂CH₂Cl is 1-chlorobutane (4 carbons). Hydrolysis with aqueous alkali yields an alcohol (butan-1-ol). Treatment with HCl(aq) does not convert a halogenoalkane into a carboxylic acid.

🧠 Exam Technique

Always count the total number of carbon atoms in the starting molecule, paying special attention to nitriles where the carbon in the -CN group counts towards the longest chain length!

❌ Common Errors

Students frequently fall into the trap of assuming nitriles produce an acid with the same number of carbons as the alkyl chain attached, forgetting that the nitrile carbon itself becomes part of the carboxylic acid functional group, increasing the total chain length by 1.

Mark Allocation: 1 mark available (AO1.2 - Demonstrating knowledge and understanding of organic reaction pathways).

Topics

Module 6: Organic chemistry and analysis · Module 4: Core organic chemistry · 6.1 Aromatic compounds, carbonyls and acids · 6.2 Nitrogen compounds, polymers and synthesis · 4.2 Alcohols, haloalkanes and analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.