Organic chemistry · GCSE Chemistry
Esters
GCSE Chemistry revision on esters: esterification from alcohol and carboxylic acid, naming ethyl ethanoate, reversible acid-catalysed conditions, uses in flavourings, and hydrolysis back to acid and alcohol.
Acid + alcohol ⇌ ester + water, concentrated H₂SO₄ catalyst, warm. Name: alkyl from alcohol, -anoate from acid. Ethanol + ethanoic → ethyl ethanoate. Sweet smell = ester test clue.
The important bits
What you need to know
- 1
Esters are organic compounds with the –COO– functional group (ester link). They are often sweet- or fruit-smelling liquids, unlike the vinegar smell of carboxylic acids or the smell of alcohols.
- 2
Esters form by esterification: carboxylic acid + alcohol ⇌ ester + water. The reaction is reversible. A strong acid catalyst (usually concentrated sulfuric acid) is used, and the mixture is warmed.
- 3
Concentrated sulfuric acid acts as a catalyst and helps remove water, shifting the equilibrium towards the ester. It must not be described as a reactant that gets used up.
- 4
Naming: the alcohol part gives the alkyl name (methyl, ethyl, propyl); the acid part gives the –anoate ending (methanoate, ethanoate, propanoate). Ethanol + ethanoic acid → ethyl ethanoate.
- 5
Displayed formulae: the ester link is –COO– between the acid-derived carbonyl carbon and the alcohol-derived alkyl group. CH₃COOC₂H₅ is ethyl ethanoate.
- 6
Uses: flavourings and fragrances (banana, pear, pineapple smells are often esters), solvents, and in making plastics such as polyester on Triple courses. Many are found naturally in fruit.
- 7
Hydrolysis reverses esterification: ester + water → acid + alcohol, often with acid or alkali catalyst. Alkaline hydrolysis produces a carboxylate salt instead of the free acid — soap making uses this idea.
- 8
Esters do not decolourise bromine water (no C=C). They burn to CO₂ and H₂O like other organic compounds. They are not acids, though they are made from acids.
Quotations worth analysing
Short evidence. Real method.
“carboxylic acid + alcohol ⇌ ester + water (acid catalyst)”
Reversible arrow, water as product, and catalyst are three separate marks. Warm the mixture in questions that ask for conditions.
“Ethanol and ethanoic acid produce ethyl ethanoate and water.”
Ethyl comes from ethanol; ethanoate from ethanoic acid. Do not call the product “ethyl ethanoic acid”.
“Concentrated sulfuric acid is a catalyst in esterification.”
It also absorbs water to favour products. Do not balance it as a reactant that is consumed.
Go deeper
How do I name an ester from two names on the paper?
Split the name at –yl and –anoate if it is already an ester name: ethyl ethanoate → ethyl from ethanol, ethanoate from ethanoic acid. If given reactants, identify the alcohol (–OH on a carbon chain, not –COOH) and the acid (–COOH). Methanol + butanoic acid → methyl butanoate. Propanol + methanoic acid → propyl methanoate. The –COO– group connects the carbonyl carbon (from the acid) to the O–alkyl part (from the alcohol). In displayed formulae, draw the C=O on the acid side of the link. Examiners penalise swapping the two halves.
Go deeper
What does the practical look like in words?
Add ethanol, ethanoic acid and a few drops of concentrated sulfuric acid to a test tube. Warm gently in a water bath — not direct flame on the acid. Pour into water: a sweet-smelling oily layer of ester may form on top; unreacted acid and alcohol dissolve or mix. The smell is the qualitative test. Safety: sulfuric acid is corrosive; ethanol is flammable. For evaluation, say reversible so yield is limited, catalyst speeds attainment of equilibrium, removing water improves yield. Distillation can separate the ester on Triple extension papers. Do not claim the reaction goes to completion without removing water.
Go deeper
How is an ester different from an alcohol or a carboxylic acid?
Alcohols have –OH attached to a carbon that is not part of a carboxyl group. Acids have –COOH and are weak acids that fizz with carbonates. Esters have –COO– with no acidic H on that oxygen; they do not fizz with carbonate. All three contain oxygen, which is why students confuse them. Functional group test: carbonate fizz → acid. Sweet smell after warming with acid catalyst → likely ester. Sodium metal fizzes with alcohols and acids (H₂) but esterification is the named reaction for making esters. In multiple choice, –COOC₂H₅ is an ester; C₂H₅OH is an alcohol; CH₃COOH is an acid.
See the idea in action
Name the ester formed from propanol and ethanoic acid, and write the word equation. Alcohol part: propyl. Acid part: ethanoate. Product: propyl ethanoate + water. Word equation: ethanoic acid + propanol ⇌ propyl ethanoate + water (concentrated sulfuric acid catalyst, warm). Reverse hydrolysis: propyl ethanoate + water → ethanoic acid + propanol. The student who writes “propyl ethanoic acid” has mixed acid and ester endings.
Exam technique
Turn knowledge into marks
Learn ethyl ethanoate as the standard example. Always include water and the reversible arrow. Name both halves of the ester from the alcohol and acid reactants. Mention concentrated sulfuric acid as catalyst when conditions are asked.
Common mistakes
Do not give these marks away
- 01
Forgetting water as a product, or omitting the reversible arrow.
- 02
Naming the ester from only one reactant (e.g. “ethyl acid”).
- 03
Calling sulfuric acid a reactant rather than a catalyst, or confusing –COO– with –COOH.
What are the products when ethanol reacts with ethanoic acid in esterification?
AEthane and water
BEthyl ethanoate and water
CEthene and steam
DSodium ethanoate and hydrogen
Show the answer
Ethyl ethanoate and water. Esterification produces an ester and water. Ethyl comes from ethanol; ethanoate from ethanoic acid. Ethene and ethane are not formed in this reaction.
Quick questions
If this is the bit you searched
How do you make an ester GCSE Chemistry?
Warm a carboxylic acid with an alcohol and a concentrated sulfuric acid catalyst. The products are an ester and water. The reaction is reversible.
How do you name ethyl ethanoate?
Ethyl from the alcohol ethanol; ethanoate from the acid ethanoic acid. The ester link joins them.
Why do esters smell fruity?
Many small esters have sweet, fruit-like odours. They are used in flavourings and perfumes. The smell helps identify esterification in school practicals.
What is hydrolysis of an ester?
Reaction with water that breaks the ester back into a carboxylic acid (or salt) and an alcohol — the reverse of esterification.