Methanoic acid is a carboxylic acid found naturally in ant venom. A student investigates the properties of methanoic acid by reacting it with several substances. Describe the properties of methanoic acid as a carboxylic acid, including its reactions with magnesium, sodium carbonate, and sodium hydroxide.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Methanoic acid is the simplest member of the homologous series of carboxylic acids, containing the functional group –COOH. It is a weak acid found in ant and bee venom and is used industrially as a preservative.
Model answer (5 marks)
Carboxylic acids are weak acids; they only partially dissociate in water, so the concentration of H⁺ is lower than that of the acid.
Methanoic acid reacts with magnesium metal to give magnesium methanoate and hydrogen gas:
CH₃COOH + Mg → Mg(CH₃COO)₂ + H₂↑
With sodium carbonate it gives sodium methanoate, water and carbon dioxide:
2 CH₃COOH + Na₂CO₃ → 2 NaCH₃COO + H₂O + CO₂↑
With sodium hydroxide it undergoes a neutralisation reaction to form sodium methanoate and water:
CH₃COOH + NaOH → NaCH₃COO + H₂O
Methanoic acid is the simplest member of the homologous series of carboxylic acids, all of which contain the –COOH functional group and share these acidic properties.
Methanoic acid reacts with magnesium metal to give magnesium methanoate and hydrogen gas:
CH₃COOH + Mg → Mg(CH₃COO)₂ + H₂↑
With sodium carbonate it gives sodium methanoate, water and carbon dioxide:
2 CH₃COOH + Na₂CO₃ → 2 NaCH₃COO + H₂O + CO₂↑
With sodium hydroxide it undergoes a neutralisation reaction to form sodium methanoate and water:
CH₃COOH + NaOH → NaCH₃COO + H₂O
Methanoic acid is the simplest member of the homologous series of carboxylic acids, all of which contain the –COOH functional group and share these acidic properties.
Examiner tips
- Use the exact reaction equations, including products and gas symbols.
- Show the acid–base nature of the reactions – mention ‘weak acid’ and ‘partial dissociation’.
- Keep the answer concise; each point should be a short sentence or equation.
Mark scheme (5 marks)
- Carboxylic acids are weak acids / partially dissociate in water / do not fully ionise
- Methanoic acid reacts with magnesium to produce a salt (magnesium methanoate) and hydrogen gas
- Methanoic acid reacts with sodium carbonate to produce a salt (sodium methanoate), water, and carbon dioxide
- Methanoic acid reacts with sodium hydroxide in a neutralisation reaction to produce a salt (sodium methanoate) and water
- Methanoic acid is part of a homologous series with the functional group –COOH / carboxylic acids have typical acidic properties
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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