Ethanoic acid is a carboxylic acid. Describe the typical acidic properties of ethanoic acid, including observations where relevant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethanoic acid is the second member of the homologous series of carboxylic acids. It is a weak acid found in vinegar.
Model answer (4 marks)
Ethanoic acid reacts with metals such as magnesium or zinc to give a metal acetate and hydrogen gas:
\[\mathrm{CH_3COOH + Mg \rightarrow CH_3COO^-Mg^{2+} + H_2}\]
It reacts with carbonates, e.g. calcium carbonate, to give a salt, water and carbon dioxide:
\[\mathrm{2CH_3COOH + CaCO_3 \rightarrow Ca(CH_3COO)_2 + CO_2 + H_2O}\]
When it reacts with a base such as sodium hydroxide it is neutralised to give a salt and water:
\[\mathrm{CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O}\]
A solution of ethanoic acid has a pH below 7, turns red litmus paper red and changes a universal indicator to red or orange.
\[\mathrm{CH_3COOH + Mg \rightarrow CH_3COO^-Mg^{2+} + H_2}\]
It reacts with carbonates, e.g. calcium carbonate, to give a salt, water and carbon dioxide:
\[\mathrm{2CH_3COOH + CaCO_3 \rightarrow Ca(CH_3COO)_2 + CO_2 + H_2O}\]
When it reacts with a base such as sodium hydroxide it is neutralised to give a salt and water:
\[\mathrm{CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O}\]
A solution of ethanoic acid has a pH below 7, turns red litmus paper red and changes a universal indicator to red or orange.
Examiner tips
- Use the correct reaction equations for each type of reaction; include the products. Mention the pH value range and indicator colour change. Keep the answer concise and use proper chemical notation.
Common mistakes
- Writing the wrong products (e.g. missing the salt or CO₂). Forgetting to state that the solution is acidic (pH < 7). Using the wrong indicator colour or omitting the indicator change.
Mark scheme (4 marks)
- Ethanoic acid reacts with metals (e.g. magnesium/zinc) to produce a salt and hydrogen gas
- Ethanoic acid reacts with carbonates (e.g. calcium carbonate) to produce a salt, water and carbon dioxide
- Ethanoic acid reacts with bases/alkalis (e.g. sodium hydroxide) to produce a salt and water (neutralisation)
- Ethanoic acid solution has a pH below 7 / turns litmus red / turns universal indicator red or orange
Key terms in this question
Related
- All Pearson Edexcel International GCSE Chemistry (4CH1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Carboxylic acids questions
- Carboxylic acids form a homologous series. State the functional group present in…
- Butanoic acid is a carboxylic acid. A student adds an excess of sodium carbonate…
- Propanoic acid is a member of the carboxylic acids homologous series. A student …
- Ethanol can be converted into ethanoic acid by microbial oxidation. Ethanoic aci…