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4.7.2Organic Chemistry

Practical: Preparation of Ethyl Ethanoate — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 6 parts Lesson 17 of 18 Unit quiz

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Part 1 of 6The Reaction

4.7.2 Practical: Preparation of Ethyl Ethanoate

An alcohol and a carboxylic acid react to form an ester and water.

Equation
  • CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O, an esterification reaction.
Catalyst
  • A few drops of concentrated sulfuric acid act as the catalyst.
Reversible
  • The reaction is reversible, so it does not go to completion unless the product is removed.
Ester
  • Ethyl ethanoate is a volatile ester with a sweet, fruity smell.

Part 2 of 6Method

Removing the ester as it forms prevents the reverse reaction.

1
Mix ethanoic acid, ethanol and a little concentrated sulfuric acid in a flask.
2
Warm the mixture gently using a water bath or electric heater, not a naked flame, because ethanol is flammable.
3
Distil the ester off as soon as it forms and collect it by condensation in a beaker.
4
Smell the distillate carefully to check for the fruity odour of an ester.
5
Add sodium carbonate solution until fizzing stops, to remove acidic impurities.
6
Add calcium chloride solution to remove leftover ethanol.

Part 3 of 6Why the Method Works

Why the Method Works
Low boiling point
  • Esters are volatile and boil at lower temperatures than the acid, so they distil over first.
Le Chatelier
  • Removing the product shifts the equilibrium towards the ester, increasing yield.
Sodium carbonate
  • It reacts with the acid impurities and produces carbon dioxide, so fizzing shows when they are removed.
Water bath
  • A water bath avoids open flames and gives gentle, even heating.
SubstanceRole
Ethanoic acidCarboxylic acid reactant
EthanolAlcohol reactant
Conc. sulfuric acidCatalyst
Sodium carbonateNeutralises acidic impurities

Part 4 of 6Safety and Evaluation

Safety and Evaluation
Fire risk
  • Ethanol and the ester are flammable, so keep naked flames away.
Corrosive
  • Concentrated sulfuric acid and ethanoic acid are corrosive, so wear eye protection.
Yield
  • Percentage yield is less than 100% because of the reversible reaction and transfer losses.

Part 5 of 6Worked Example

Question

  • 4.6 g of ethanol reacts with excess ethanoic acid and 5.3 g of ethyl ethanoate is obtained.
  • Calculate the percentage yield.
  • (Ar: C = 12, H = 1, O = 16)

  1. Mr of ethanol C₂H₅OH = 46, so moles = 4.6 ÷ 46 = 0.10 mol.
  2. One mole of ethanol gives one mole of ester, so theoretical moles of CH₃COOC₂H₅ = 0.10 mol.
  3. Mr of ethyl ethanoate C₄H₈O₂ = (4 × 12) + 8 + 32 = 88, so theoretical mass = 0.10 × 88 = 8.8 g.
  4. Percentage yield = 5.3 ÷ 8.8 × 100 = 60%.

Answer Percentage yield = 60% (to 2 s.f.)

Part 6 of 6Exam Checklist & Tips

4.7.2 – Key Points for the Exam

  • Ester An organic compound with the –COO– linkage, formed from a carboxylic acid and an alcohol.
  • Esterification The reaction of a carboxylic acid with an alcohol to make an ester.
  • Distillation Separation of liquids by evaporation and condensation.
  • Volatile Evaporating easily at low temperatures.

Common Mistakes

  • Heating the flammable mixture with a Bunsen burner.
  • Forgetting that the reaction is reversible and needs the ester removed.
  • Using sulfuric acid as a reactant rather than as a catalyst.
  • Adding sodium carbonate solution to the ester without waiting until the fizzing stops, leaving acid impurities.

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