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4.8.3Unit 4. Rates, Equilibria and Further Organic Chemistry

Reactions of Carboxylic Acids — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 4 parts Lesson 47 of 56 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
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Curriculum Equation Key pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: pH + pOH = 14
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Part 1 of 4Acid Reactions

4.8.3 Reactions of Carboxylic Acids

Carboxylic acids are weak acids but show typical acid reactions with metals, bases and carbonates.

With metals
  • 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂, so magnesium dissolves with effervescence.
With bases
  • CH₃COOH + NaOH → CH₃COONa + H₂O, forming a carboxylate salt and water.
With carbonates
  • 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂, giving fizzing, which is a test for the acid group.
Salt name
  • The salt formed is a carboxylate, such as sodium ethanoate, with the ending -oate.
Test for acids
  • Fizzing with sodium hydrogencarbonate solution distinguishes a carboxylic acid from most alcohols, which do not react with carbonates.

Part 2 of 4Other Reactions

Other Reactions
Esterification
  • An acid and an alcohol heated with concentrated H₂SO₄ catalyst form an ester and water in a reversible reaction.
Reduction
  • LiAlH₄ in dry ether reduces carboxylic acids to primary alcohols: CH₃COOH + 4[H] → CH₃CH₂OH + H₂O.
Acyl chloride formation
  • PCl₅ reacts at room temperatureCH₃COOH + PCl₅ → CH₃COCl + POCl₃ + HCl.
Strength
  • NaBH₄ cannot reduce carboxylic acids, so a stronger reducing agent is required.

Part 3 of 4Esterification in Detail

1
Mix the carboxylic acid and the alcohol with a few drops of concentrated sulfuric acid as a catalyst.
2
Heat the mixture under reflux, because the reaction is slow and the reagents are volatile.
3
The reaction reaches equilibrium: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O.
4
Distil off the ester, which has a lower boiling point than the acid, and wash it with sodium carbonate solution.

Part 4 of 4Exam Checklist & Tips

4.8.3 – Key Points for the Exam

  • Carboxylate The anion RCOO⁻ or its salt.
  • Esterification Reaction of an acid and an alcohol to form an ester.
  • Reflux Heating with continuous condensation of vapours.
  • Effervescence Fizzing caused by gas release.

Common Mistakes

  • Writing a carbonate reaction without CO₂ and water.
  • Using NaBH₄ to reduce a carboxylic acid.
  • Forgetting the sulfuric acid catalyst in esterification.
  • Giving the salt the ending -ate rather than -oate.

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