IGCSE · Practice questions · Carboxylic acids and esters

Acids, oxidation and esters.

Six original Cambridge-style questions on ethanoic acid and esters.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Weak acid, oxidised alcohol, fruity ester.

Ethanoic acid: weak acid; metal, base, carbonate give ethanoates.
Extended, oxidation: acidified KMnO₄ (purple to colourless) or bacteria in air.
Extended, esterification: acid + alcohol ⇌ ester + water, conc. H₂SO₄ catalyst.
Naming: alcohol part first (ethyl), acid part second (ethanoate).

Recall

[2 marks]

Write a word equation and a balanced equation for the reaction between ethanoic acid and sodium hydroxide.

ethanoic acid + sodium hydroxide → sodium ethanoate + water ✓
CH₃COOH + NaOH → CH₃COONa + H₂O ✓

Recall

[2 marks]

Ethanoic acid is added to sodium carbonate. Describe what is seen and name the gas produced.

Fizzing (effervescence) as the solid dissolves. ✓
Carbon dioxide (turns limewater milky). ✓

Explain

[2 marks]

Explain why ethanoic acid is classed as a weak acid, and how its pH compares with hydrochloric acid of the same concentration.

It is only partially dissociated (ionised) in water, so few H⁺ ions are released. ✓
Its pH is higher than that of hydrochloric acid of the same concentration. ✓

Recall

[3 marks]

(Extended) Describe two ways of converting ethanol into ethanoic acid.

Warm ethanol with acidified aqueous potassium manganate(VII). ✓
The solution changes from purple to colourless. ✓
Bacterial oxidation: leave ethanol solution (such as wine) exposed to air so bacteria oxidise it to vinegar. ✓

Analysis

[3 marks]

(Extended) Ethanol reacts with ethanoic acid when warmed with a few drops of concentrated sulfuric acid. Write the equation, name the organic product and state the role of the sulfuric acid.

CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O ✓
Product: ethyl ethanoate (an ester). ✓
Sulfuric acid is a catalyst. ✓

Analysis

[2 marks]

(Extended) Name the esters formed from (a) methanol and ethanoic acid, (b) ethanol and propanoic acid.

(a) methyl ethanoate. ✓
(b) ethyl propanoate. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.