OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2017: Question 10

1 mark · Medium difficulty · Multiple Choice

Identify which of the four given compounds (amide, carboxylic acid, ester, acyl chloride) produces the most acidic solution when equal amounts are added to water

Practise this question

Question

Multiple choice question 10 asking which compound would produce the most acidic solution when equal amounts are added to the same volume of water. The options are A: CH3CONH2, B: CH3COOH, C: CH3COOCH3, and D: CH3COCl.
Question text

10 Equal amounts of the four compounds are added to the same volume of water.

Which compound would produce the most acidic solution?

A CH3CONH2

B CH3COOH

C CH3COOCH3

D CH3COCl

Your answer

[1]

Mark scheme

Show the mark scheme Mark scheme table showing the correct answer for question 10 is D, worth 1 mark.

10 D 1

How to answer it

Comparing Acidity of Carbonyl Derivatives in Water

What this question tests

This question assesses your understanding of the chemical reactions of acyl chlorides, carboxylic acids, esters, and amides with water, specifically focusing on the stoichiometry of their hydrolysis reactions and the resulting hydrogen ion concentration (acidity) of the solution.

Question 10 Multiple Choice

Solution and Analysis

✅ Correct Answer: D

CH₃COCl produces the most acidic solution because it reacts violently/completely with water to produce two moles of acid per mole of reactant (one mole of CH₃COOH and one mole of HCl , a strong acid).

💡 Key Knowledge

  • Acyl chlorides ( CH₃COCl ): Hydrolyse rapidly and completely with water to form a carboxylic acid and steamy acidic fumes of hydrogen chloride ( HCl ).
  • Carboxylic acids ( CH₃COOH ): Weak acids that partially dissociate in water.
  • Esters ( CH₃COOCH₃ ): Undergo slow, reversible hydrolysis.
  • Amides ( CH₃CONH₂ ): Hydrolyse very slowly under neutral conditions.

🧠 Exam Technique

When asked about the "most acidic solution" from equal amounts of substances added to the same volume of water, look for:

  • Presence of strong acid products (like HCl ).
  • The number of moles of H⁺ ions released per mole of original compound.

❌ Common Errors

Students often incorrectly choose CH₃COOH (Option B) simply because it already has the word "acid" in its name, forgetting that acyl chlorides generate both a carboxylic acid and hydrochloric acid upon reacting with moisture.

Mark Scheme Allocation: 1 mark for selecting D. No working required as it is a multiple-choice question.

Topics

Module 6: Organic chemistry and analysis · 6.1 Aromatic compounds, carbonyls and acids

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2017. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.