Ester – IGCSE Chemistry Definition
IGCSE Chemistry definition of ester: an organic compound formed from an acid and alcohol. Covers naming, formation, uses, and exam tips for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Esters link the alcohol and carboxylic acid topics and are a favourite for Paper 4 questions. The naming convention, formation equation, and typical uses are all regularly examined.
The 0620 definition
An ester is an organic compound formed by the reaction of a carboxylic acid with an alcohol, with the loss of water. Esters contain the functional group −COO−.
Formation of esters (esterification)
General equation:
Carboxylic acid + alcohol ⇌ ester + water
Example:
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
(Ethanoic acid + ethanol → ethyl ethanoate + water)
Conditions: concentrated sulfuric acid catalyst, gentle warming. The reaction is reversible.
Naming esters
The ester name has two parts:
- First part: from the alcohol, ending in −yl (methyl, ethyl, propyl)
- Second part: from the acid, ending in −anoate (methanoate, ethanoate, propanoate)
| Acid | Alcohol | Ester name | Formula |
|---|---|---|---|
| Methanoic acid | Methanol | Methyl methanoate | HCOOCH₃ |
| Ethanoic acid | Ethanol | Ethyl ethanoate | CH₃COOC₂H₅ |
| Ethanoic acid | Methanol | Methyl ethanoate | CH₃COOCH₃ |
| Propanoic acid | Ethanol | Ethyl propanoate | C₂H₅COOC₂H₅ |
Properties and uses of esters
| Property | Detail |
|---|---|
| Smell | Sweet, fruity — many artificial flavourings are esters |
| Solubility | Slightly soluble in water; miscible with organic solvents |
| Volatility | Relatively volatile (low boiling points) |
Uses:
- Flavourings and fragrances in food and perfumes
- Solvents for paints, varnishes, and nail polish remover
- Polyester manufacture (condensation polymerisation of diesters)
Worked exam question
Ethanol reacts with propanoic acid. (a) Name the ester formed. [1] (b) State the catalyst used. [1] (c) State one use of esters. [1]
Mark scheme
(a) Ethyl propanoate [1]
(b) Concentrated sulfuric acid [1]
(c) Flavourings / fragrances / solvents [1]
Common exam mistakes
- Reversing the ester name — the alcohol part comes first (−yl), the acid part comes second (−anoate). Ethanol + ethanoic acid = ethyl ethanoate, not ethanoyl ethane.
- Forgetting the catalyst — concentrated sulfuric acid is required for esterification.
- Confusing ester formation with neutralisation — neutralisation involves inorganic acids and bases; esterification is an organic reaction.
Studying this yourself? Tutoring arrangements are normally made by a parent or guardian. Message us for the details to share with them, or send them this page.