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4.6.2Organic Chemistry

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

5 min read 5 parts Lesson 16 of 18 Unit quiz

📚 Edexcel Linear - OL (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 5Carboxylic Acids as Acids

4.6.2 Reactions of Carboxylic Acids

The properties of carboxylic acids mirror those of common mineral acids, though they react more slowly.

Functional group
  • Carboxylic acids contain the –COOH group, and the hydrogen can be released as H⁺ in water.
Weak acids
  • They only partially ionise, so they are weak acids with a higher pH than a strong acid of the same concentration.
Typical acid reactions
  • They behave like other acids, reacting with reactive metals and with carbonates.
Naming salts
  • The salts are named by changing -oic acid to -oate, so ethanoic acid gives ethanoates.

Part 2 of 5Reaction with Metals

Reaction with Metals
General pattern
  • Carboxylic acid + reactive metal → metal carboxylate + hydrogen.
Magnesium
  • 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂, forming magnesium ethanoate.
Observation
  • Bubbles of hydrogen are seen, which burn with a squeaky pop.
Rate
  • The reaction is slower than with a strong acid of the same concentration because fewer H⁺ ions are present.
AcidSalt nameFormula of ion
MethanoicMethanoateHCOO⁻
EthanoicEthanoateCH₃COO⁻
ButanoicButanoateCH₃CH₂CH₂COO⁻

Part 3 of 5Reaction with Carbonates

Reaction with Carbonates
General pattern
  • Carboxylic acid + metal carbonate → metal carboxylate + water + carbon dioxide.
Sodium carbonate
  • 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.
Potassium carbonate
  • 2CH₃CH₂CH₂COOH + K₂CO₃ → 2CH₃CH₂CH₂COOK + H₂O + CO₂.
Observation
  • The mixture fizzes, and the gas turns limewater cloudy.

Part 4 of 5Writing an Equation

1
Identify the acid and write its formula with the –COOH group shown.
2
Name the salt by replacing -oic acid with -oate and adding the metal name first.
3
Write the formula of the salt, with the metal replacing the hydrogen of the –COOH group.
4
Balance the equation, remembering that each –COOH loses one hydrogen.
5
Add the other products: hydrogen for metals, or water and carbon dioxide for carbonates.

Part 5 of 5Exam Checklist & Tips

4.6.2 – Key Points for the Exam

  • Carboxylic acid An organic compound containing the –COOH functional group.
  • Weak acid An acid that is only partially ionised in water.
  • Carboxylate The salt formed from a carboxylic acid, with name ending -oate.
  • Functional group The atom or group of atoms that determines the reactions of an organic compound.

Common Mistakes

  • Naming the salt as ethanoic instead of ethanoate.
  • Forgetting that two moles of acid are needed per mole of carbonate.
  • Saying carboxylic acids are strong acids.
  • Missing the water in the products of the carbonate reaction.

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