OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2022: Question 10

1 mark · Medium difficulty · Multiple Choice

Identify one of the products formed from the hydrolysis of butyl propanoate by aqueous sodium hydroxide.

Practise this question

Question

Multiple choice question asking which compound is one of the products of the hydrolysis of butyl propanoate by aqueous sodium hydroxide. Four options are given: A: C3H7ONa, B: C3H5O2Na, C: C4H9ONa, and D: C4H7O2Na, with a box to write the answer and a mark value of [1] at the bottom right.
Question text

10 Butyl propanoate is hydrolysed by aqueous sodium hydroxide.

Which compound is one of the products of this hydrolysis?

A C3H7ONa

B C3H5O2Na

C C4H9ONa

D C4H7O2Na

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme shows question number 10 with the correct answer B, worth 1 mark and assessment objective AO1.2.

10 B 1 AO1.2

How to answer it

Hydrolysis of Butyl Propanoate

What this question tests

This question assesses your understanding of organic reaction mechanisms, specifically the alkaline hydrolysis (saponification) of esters. You must be able to break down IUPAC ester names into their constituent alcohol and carboxylic acid parts, determine molecular formulas, and account for the sodium salt product formed under basic conditions.

Question 10

Alkaline Ester Hydrolysis

✅ Correct Answer: B

The correct option is B ( C₃H₅O₂Na ).

Butyl propanoate hydrolyses in aqueous sodium hydroxide to form butan-1-ol ( C₄H₉OH ) and sodium propanoate ( C₂H₅COONa , which simplifies to molecular formula C₃H₅O₂Na ).

💡 Key Knowledge

  • Ester Structure: Named as [Alcohol part] [Carboxylic acid part]-oate. Butyl propanoate comes from butan-1-ol and propanoic acid.
  • Alkaline Conditions: Hydrolysis with aqueous NaOH is base-catalyzed and irreversible, yielding a carboxylate salt and an alcohol.

🧠 Exam Technique

Dissect the ester name from right to left:

  • Propanoate (Acid part): Propane- means 3 carbons ( CH₃CH₂COO⁻ ).
  • Butyl (Alcohol part): Butyl- means 4 carbons ( C₄H₉ ).
  • Match the molecular formulas carefully against the multiple-choice options to avoid carbon-counting errors.

❌ Common Errors

  • Counting the wrong chain: Selecting option D ( C₄H₇O₂Na ) because students mistakenly assign the 4-carbon butyl group to the carboxylic acid salt instead of the alcohol product.
  • Forgetting the sodium: Confusing alkaline hydrolysis with acidic hydrolysis, which yields the neutral carboxylic acid rather than its sodium salt.
Mark Scheme Allocation: 1 mark awarded for selecting B (AO1.2 - Demonstrating knowledge and understanding of organic reaction products).

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 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.