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10.5.3Chemistry of the Environment

Esters — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 7 of 7 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
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Part 1 of 5The Ester Group

10.5.3 Esters

Esters are formed from a carboxylic acid and an alcohol, and they have a characteristic functional group.

Functional group
  • Esters contain the –COO– group, which links two hydrocarbon parts of the molecule.
Formation
  • An ester forms when a carboxylic acid reacts with an alcohol in the presence of concentrated sulfuric acid as a catalyst.
Water
  • Water is also formed in each esterification reaction, so the reaction is a condensation.
Recognition
  • An ester can be recognised by its name, which ends in -oate, or by its structural formula.

Part 2 of 5Making Ethyl Ethanoate

Ethyl ethanoate is a common example of an ester made in the laboratory.

1
Ethanoic acid and ethanol are mixed in a flask with a few drops of concentrated sulfuric acid as a catalyst.
2
The mixture is warmed gently so that the reaction takes place at a reasonable rate.
3
The ester forms along with water, and the ethyl ethanoate can be separated by distillation because it is volatile.
4
The overall equation is CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O.

Part 3 of 5Properties and Uses

Properties and Uses
Smell
  • Esters are sweet-smelling, so they are used in food flavourings and perfumes.
Volatility
  • Esters are volatile, which means they evaporate easily, so their smell reaches us quickly.
Physical state
  • Esters are usually oily liquids at room temperature.
Naming
  • Ethyl ethanoate is named from ethanol (ethyl) and ethanoic acid (ethanoate).

Part 4 of 5Worked Example

Question Name the ester formed when propanoic acid, C₂H₅COOH, reacts with methanol, CH₃OH, and write the equation.

  1. Name the esterthe alcohol part gives 'methyl' and the acid part gives 'propanoate', so the name is methyl propanoate.
  2. Write the equationC₂H₅COOH + CH₃OH → C₂H₅COOCH₃ + H₂O.
  3. Check the carbon atoms3 + 1 = 4 on the left and 4 on the right.
  4. Check the hydrogen atoms6 + 4 = 10 on the left and 8 + 2 = 10 on the right.

Answer The ester is methyl propanoate: C₂H₅COOH + CH₃OH → C₂H₅COOCH₃ + H₂O.

Part 5 of 5Exam Checklist & Tips

10.5.3 – Key Points for the Exam

  • Ester A compound containing the –COO– functional group, formed from a carboxylic acid and an alcohol.
  • Esterification The reaction of a carboxylic acid with an alcohol to form an ester and water.
  • Ester group The –COO– group that characterises esters.
  • Volatile Describes a substance that evaporates easily.
  • Catalyst A substance that speeds up a reaction without being used up.

Common Mistakes

  • Naming an ester with the word acid instead of -oate, such as writing ethyl ethanoic acid.
  • Forgetting that water is a product of esterification.
  • Using dilute sulfuric acid as the catalyst; concentrated sulfuric acid is required.
  • Confusing the –COO– group in an ester with the –COOH group of a carboxylic acid.

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