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*Revision Materials and Past Papers* 1 Atomic Structure and the Periodic Table 2 Bonding and Structure 3 Redox I 4 Inorganic Chemistry and the Periodic Table 5 Formulae, Equations and Amounts of Substance 6 Organic Chemistry I 7 Modern Analytical Techniques I 8 Energetics I 9 Kinetics I 10 Equilibrium I 11 Equilibrium II 12 Acid-base Equilibria 13 Energetics II 14 Redox II 15 Transition Metals 16 Kinetics II 17 Organic Chemistry II 18 Organic Chemistry III 19 Modern Analytical Techniques II RP Required Practicals

Required Practicals

1 Measuring the molar volume of a gas 2 Preparation of a standard solution from a solid acid 3 Finding the concentration of a solution of hydrochloric acid 4 Investigation of the rates of hydrolysis of halogenoalkanes 5 The oxidation of ethanol 6 Chlorination of 2-methylpropan-2-ol with concentrated hydrochloric acid 7 Analysis of some inorganic and organic unknowns 8 To determine the enthalpy change of a reaction using Hess’s Law 9 Finding the Ka value for a weak acid 10 Investigating some electrochemical cells 11 Redox titration 12 The preparation of a transition metal complex 13 Following the rate of the iodine-propanone reaction by titrimetric method and investigating a clock reaction (Harcourt-Esson iodine clock) 14 Finding the activation energy of a reaction 15 Analysis of some inorganic and organic unknowns 16 The preparation of aspirin

Core Practical 16 – Synthesis of Aspirin

Aim:
  • To synthesise aspirin (acetylsalicylic acid) from 2-hydroxybenzoic acid (salicylic acid)
  • To understand the reaction mechanism of acid anhydrides
  • To purify the product by recrystallisation and assess purity using melting point
    •

Reaction Overview

Safety Precautions

Apparatus and Chemicals

Procedure

Adding reagents for aspirin synthesis to a pear-shaped flask Edexcel A-level Chemistry Core Practical 16 Making Aspirin.
  1. Weigh 2.0 g of 2-hydroxybenzoic acid into a pear-shaped flask.
  2. Add 5.0 cm³ of ethanoic anhydride.
  3. Add 5 drops of concentrated sulfuric acid.
  4. Fit a condenser and gently heat the mixture in a water bath until all solid dissolves.
  5. Continue heating for 10 minutes.
  6. Remove from heat, add ~10 cm³ crushed ice and distilled water.
  7. Cool in an ice bath to complete crystallisation.
Reflux setup for aspirin preparation Edexcel A-level Chemistry Core Practical 16 Making Aspirin.
  1. Filter crystals using a Büchner funnel with suction.
Crude aspirin collected after vacuum filtration Edexcel A-level Chemistry Core Practical 16 Making Aspirin.
  1. Wash crystals with a minimum amount of iced water.
  2. Recrystallise the product in a minimum amount of warm ethanol:water (1:3).
Recrystallisation of aspirin using ethanol-water mixture Edexcel A-level Chemistry Core Practical 16 Making Aspirin.
  1. Filter and dry the pure aspirin.
  2. Measure mass and the melting point range of the product.
Measuring melting point of purified aspirin Edexcel A-level Chemistry Core Practical 16 Making Aspirin.

Calculations

Step 1 – Relative Molecular Masses
Mr (2-hydroxybenzoic acid) = 138;  Mr (aspirin) = 180

Step 2 – Theoretical yield
Using 2.0 g of salicylic acid:
moles = 2.0 ÷ 138 = 0.01449 mol
Theoretical mass of aspirin = 0.01449 × 180 = 2.61 g

Step 3 – Percentage yield
% yield = (actual yield ÷ 2.61) × 100
Example: 2.1 g aspirin → (2.1 ÷ 2.61) × 100 ≈ 81%

Melting Point Test

Example data: Melting range 132–135 °C → likely impure sample.

Sources of Impurity

Common Questions