Ethanol is an alcohol that can be oxidised to form ethanoic acid, a carboxylic acid. Describe the structure and properties of ethanoic acid, and explain what happens when it reacts with sodium carbonate solution.

Eduqas A-Level Chemistry — 2.7 Alcohols and carboxylic acids · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Ethanol is widely used as a solvent and fuel. When ethanol is oxidised, it forms ethanoic acid, which is the acid found in vinegar.

Model answer (5 marks)

Ethanoic acid (CH₃COOH) has a carboxyl group –COOH attached to a methyl group. The –COOH group makes it a weak acid; it only partially dissociates in water to give CH₃COO⁻ and H⁺.

When ethanoic acid reacts with sodium carbonate (Na₂CO₃) the acid–base reaction gives the salt sodium ethanoate (CH₃COONa) and releases carbon dioxide gas and water:

CH₃COOH + Na₂CO₃ → 2 CH₃COONa + CO₂↑ + H₂O

Examiner tips

  • Use the exact formula CH₃COOH and mention the –COOH group; mark scheme values this detail.
  • State that it is a weak acid and that it only partially dissociates; this earns the acid property point.
  • Write the balanced equation for the reaction with Na₂CO₃, including CO₂ and H₂O; this covers the salt, gas and water points.

Common mistakes

  • Writing ethanoic acid as CH₃COO⁻ instead of CH₃COOH; this omits the proton and loses the weak‑acid point.
  • Forgetting to include CO₂ or H₂O in the reaction equation; both are required for full marks.
  • Using the wrong salt name (e.g., sodium acetate instead of sodium ethanoate); the examiner expects the specific name.

Mark scheme (5 marks)

  1. Ethanoic acid contains a carboxyl group (–COOH)
  2. Ethanoic acid is a weak acid (it does not fully dissociate / ionise in water)
  3. Ethanoic acid reacts with sodium carbonate to produce a salt (sodium ethanoate)
  4. Carbon dioxide gas is also produced in the reaction with sodium carbonate
  5. Water is also produced in the reaction with sodium carbonate

Key terms in this question

carboxylic acid · sodium carbonate

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