Carboxylic Acids
Section: 11. Organic Chemistry | Syllabus: Cambridge IGCSE Chemistry (0620)
Ethanoic Acid
Ethanoic acid (CH₃COOH) is a carboxylic acid and is found in vinegar. Like all carboxylic acids it is a weak acid, but it shows the same typical reactions as any other acid: with metals, with bases, and with carbonates.
Reaction with Metals
Acid + metal → salt + hydrogen
2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂
(ethanoic acid + magnesium → magnesium ethanoate + hydrogen)
Reaction with Bases
Acid + base → salt + water (neutralisation - no gas is produced)
CH₃COOH + NaOH → CH₃COONa + H₂O
(ethanoic acid + sodium hydroxide → sodium ethanoate + water)
Reaction with Carbonates
Acid + carbonate → salt + water + carbon dioxide
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
(ethanoic acid + sodium carbonate → sodium ethanoate + water + carbon dioxide)
The salts of carboxylic acids are named by changing the "-oic acid" ending to "-oate", e.g. ethanoic acid + sodium → sodium ethanoate.
Worked Example
- Question (based on a real exam question): ethanoic acid reacts with sodium. Complete the word equation: ethanoic acid + sodium → ____ + ____.
- Answer: sodium ethanoate + hydrogen. Acid + metal → salt + hydrogen; the salt name combines the metal (sodium) with the acid's "-oate" name (ethanoate).
Common Mistakes
- ❌ Assuming every reaction of ethanoic acid produces a gas, or that acid + metal gives water as a product
- ✓ only reactions with reactive metals (giving hydrogen) and with carbonates (giving carbon dioxide) produce a gas - the reaction with a base (e.g. sodium hydroxide) is a neutralisation that produces only a salt and water, with no gas at all
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