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Edexcel IAL Chemistry 20.4 Core Practical 16 aspirin preparation

The direct evidence focuses on mechanism and work-up: H+ catalyses the acylation, and ice water removes excess ethanoic anhydride or helps crystallise aspirin.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • State H+ or concentrated sulfuric acid as a catalyst in aspirin synthesis.
  • Add curly arrows from oxygen lone pairs in the protonated acylation mechanism.
  • Explain adding ice water to remove excess ethanoic anhydride or crystallise aspirin.

20.4—CORE PRACTICAL 16 The preparation of aspirin question 1

[Maximum number: 1]

A student prepared a sample of aspirin. The equation for the reaction is shown.

Figure for Question 20.4—CORE PRACTICAL 16 The preparation of aspirin question 1 — Edexcel A-Level Chemistry A2

The aspirin was recrystallised using an ethanol-water mixture as the solvent.
The student determined its melting temperature using the apparatus shown.

Figure for Question 20.4—CORE PRACTICAL 16 The preparation of aspirin question 1 — Edexcel A-Level Chemistry A2

The student's sample melted over a range of 8 degrees starting at 125∘C125^{\circ} \mathrm{C}.
The published melting temperature of pure aspirin is 135∘C135^{\circ} \mathrm{C}.

Which is likely to be the main impurity in the sample of aspirin?

A

ethanoic acid

B

ethanoic anhydride

C

ethanol

D

2-hydroxybenzoic acid

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