11.7 Carboxylic acids
- Syllabus
- 0620–2026–2027
- Topic
- 11.7
- Level
- —
Learning objectives
11.7.1Reaction of ethanoic acid• Describe reaction of ethanoic acid with: (a) metals (b) bases (c) carbonates including names and formulae of the salts produced11.7.2Formation of ethanoic acid by the• Describe formation of ethanoic acid by the oxidation of ethanol: (a) with acidified aqueous potassium manganate(VII) (b) by bacterial oxidation during vinegar production11.7.3Reaction of a carboxylic acid with an• Describe reaction of a carboxylic acid with an alcohol using an acid catalyst to form an ester
Predict the acid reactions of ethanoic acid
| Reactant with ethanoic acid | Products | Observation |
|---|---|---|
| reactive metal | metal ethanoate + hydrogen | effervescence; metal dissolves |
| base / alkali | metal ethanoate + water | neutralisation; no gas |
| metal carbonate | metal ethanoate + water + carbon dioxide | effervescence |
The salt name ends in ethanoate. Its formula combines CH₃COO⁻ ions with the metal ion in the ratio needed for electrical neutrality.
| Reaction example | Balanced equation | Salt name |
|---|---|---|
| magnesium | 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂ | magnesium ethanoate |
| sodium hydroxide | CH₃COOH + NaOH → CH₃COONa + H₂O | sodium ethanoate |
| sodium carbonate | 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂ | sodium ethanoate |
Choose the standard acid reaction first, then construct the ethanoate formula from the metal charge and balance the complete equation.
Metals form hydrogen; carbonates form carbon dioxide and water; bases form water only. Do not interchange these gas products.
Oxidise ethanol to ethanoic acid
Ethanol is oxidised to ethanoic acid either with acidified aqueous potassium manganate(VII) or by bacterial oxidation during vinegar production.
| Route | Oxidising source / condition | Product |
|---|---|---|
| laboratory chemical oxidation | acidified aqueous potassium manganate(VII) | ethanoic acid |
| vinegar production | bacteria oxidise ethanol using oxygen from air | ethanoic acid |
The oxidation change can be represented as: C₂H₅OH + 2[O] → CH₃COOH + H₂O.
Oxidation increases the oxygen content of the organic molecule. During vinegar production, the process is biological and requires exposure to oxygen rather than anaerobic ethanol fermentation.
Do not describe this conversion as reduction or simple fermentation. The required chemical reagent is acidified aqueous potassium manganate(VII), and the vinegar route is bacterial oxidation.
Form an ester from a carboxylic acid and an alcohol
A carboxylic acid reacts with an alcohol, using an acid catalyst, to form an ester and water.
carboxylic acid + alcohol ⇌ ester + water
| Reactants | Catalyst / condition | Products |
|---|---|---|
| ethanoic acid + ethanol | concentrated sulfuric acid and heat | ethyl ethanoate + water |
| propanoic acid + methanol | acid catalyst and heat | methyl propanoate + water |
Example structural equation: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O.
The alcohol supplies the first, -yl part of the ester name; the acid supplies the second, -oate part.
Water is the second product, not hydrogen. Acidified potassium manganate(VII) oxidises alcohols; concentrated sulfuric acid is the catalyst used here for esterification.