OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2025: Question 7

1 mark · Easy difficulty · Multiple Choice

Identify the organic products formed from the acid hydrolysis of N-methylpropanamide.

Practise this question

Question

Question 7 asks: 'What are the organic products of the acid hydrolysis of CH3CH2CONHCH3?' Four options are given: A: CH3CH2COO- + CH3NH3+, B: CH3CH2COOH + CH3NH3+, C: CH3CH2COOH + CH3NH2, D: CH3CH2COO- + CH3NH2. An answer box is provided alongside a mark value of 1.
Question text

7 What are the organic products of the acid hydrolysis of CH3CH2CONHCH3?

A CH CH COO– + CH NH +

32 3 3

B CH CH COOH + CH NH +

32 3 3

C CH3CH2COOH + CH3NH2

D CH CH COO– + CH NH

32 3 2

Your answer

[1]

Mark scheme

Show the mark scheme Mark scheme for question 7 showing the correct answer is B, awarded 1 mark.

7 B 1

How to answer it

Acid Hydrolysis of Secondary Amides

What this question tests

This question tests your understanding of the hydrolysis of amides under acidic conditions. Specifically, you must identify where the amide bond cleaves and predict the correct protonation states of the resulting carboxylic acid and amine functional groups in the presence of excess aqueous acid (H⁺).

Question 7 • Multiple Choice [1 Mark]

Identifying Organic Products of Amide Hydrolysis

Substrate: N-methylpropanamide, CH₃CH₂CONHCH₃

✅ Correct Answer

B: CH₃CH₂COOH + CH₃NH₃⁺

Mark Breakdown:
[1 Mark] for selecting option B.

🧠 Exam Technique: The 2-Step Breakdown

  1. Locate the amide bond: The bond breaks between the carbonyl carbon and the nitrogen atom:
    CH₃CH₂CO —–— NHCH₃
  2. Check the reaction conditions (pH): Under acidic conditions (excess H⁺):
    • The carboxylic part remains fully protonated: CH₃CH₂COOH.
    • The basic amine part accepts H⁺ to form a substituted ammonium ion: CH₃NH₃⁺.

💡 Key Knowledge: Acid vs Alkaline Hydrolysis

Amides require heating under reflux with concentrated aqueous acid or alkali to hydrolyse:

  • Acid Hydrolysis (e.g. heated with dilute HCl):
    R-CONH-R' + H₂O + H⁺ → R-COOH + R'-NH₃⁺
    The amine acts as a base and is protonated by the excess acid.
  • Alkaline Hydrolysis (e.g. heated with aqueous NaOH):
    R-CONH-R' + OH⁻ → R-COO⁻ + R'-NH₂
    The carboxylic acid reacts with base to form a carboxylate salt; the amine remains neutral.

📐 Step-by-Step Reaction Accounting

Writing out the full stoichiometric equation helps confirm charges and atom balance:

  1. Reagents: CH₃CH₂CONHCH₃ + H₂O + H⁺
  2. Carbonyl fragment (3 carbons): Becomes propanoic acid, CH₃CH₂COOH .
  3. Amine fragment (1 carbon): Starts as CH₃NH₂ , but immediately accepts H⁺ to give CH₃NH₃⁺ (methylammonium).
  4. Net Organic Products: CH₃CH₂COOH + CH₃NH₃⁺

❌ Common Errors & Distractor Breakdown

  • Option A ( CH₃CH₂COO⁻ + CH₃NH₃⁺ ): Incorrect. A carboxylate ion cannot persist in an acidic solution; it would immediately be protonated to form carboxylic acid.
  • Option C ( CH₃CH₂COOH + CH₃NH₂ ): The most common trap. Students often recall the simple hydrolysis products without considering that methylamine ( CH₃NH₂ ) is a Brønsted–Lowry base and will readily react with H⁺ to form CH₃NH₃⁺ .
  • Option D ( CH₃CH₂COO⁻ + CH₃NH₂ ): Incorrect. These are the organic species formed under alkaline (basic) hydrolysis conditions, not acidic conditions.

Topics

Module 6: Organic chemistry and analysis · 6.2 Nitrogen compounds, polymers and synthesis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.