Ethanoic acid is a carboxylic acid that reacts with ethanol in the presence of an acid catalyst to form a sweet-smelling ester. Describe what happens when ethanoic acid reacts with ethanol to form an ester, and explain why esters are useful.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethanoic acid has the functional group –COOH. When mixed with ethanol and a few drops of concentrated sulfuric acid, a new compound with a pleasant smell is formed.
Model answer (5 marks)
Esterification is the reaction between a carboxylic acid and an alcohol.
1. The –COOH group of ethanoic acid reacts with the –OH of ethanol.
2. A water molecule is eliminated, giving the ester and H₂O.
3. Concentrated sulphuric acid acts as an acid catalyst, protonating the carbonyl and speeding the reaction.
4. Esters have pleasant, sweet aromas, so they are used as flavourings, perfumes and cosmetics.
5. Esters are also good solvents – they are found in paints, varnishes and nail‑polish removers.
1. The –COOH group of ethanoic acid reacts with the –OH of ethanol.
2. A water molecule is eliminated, giving the ester and H₂O.
3. Concentrated sulphuric acid acts as an acid catalyst, protonating the carbonyl and speeding the reaction.
4. Esters have pleasant, sweet aromas, so they are used as flavourings, perfumes and cosmetics.
5. Esters are also good solvents – they are found in paints, varnishes and nail‑polish removers.
Examiner tips
- Use the term "esterification" early. Mention water elimination and the role of the acid catalyst. Give at least one example of a useful application (flavouring or solvent).
Common mistakes
- Forgetting to state that water is produced. Calling the reaction a "synthesis" instead of "esterification". Omitting the acid catalyst or its purpose.
Mark scheme (5 marks)
- The reaction between a carboxylic acid and an alcohol is called esterification
- Water is also produced / eliminated in the reaction (alongside the ester)
- An acid catalyst (concentrated sulfuric acid) is needed / used to speed up the reaction
- Esters are used as flavourings or in perfumes / cosmetics because they have pleasant / sweet smells
- Esters are used as solvents (e.g. in paints, varnishes, or nail polish remover)
Key terms in this question
ester · carboxylic acid · catalyst
Related
- All Eduqas A-Level Chemistry revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Carboxylic acids and their derivatives questions
- Butanoic acid is a carboxylic acid responsible for the unpleasant smell of ranci…
- Ethyl ethanoate is an ester used as a solvent in nail varnish remover. Describe …
- Methanoic acid is a carboxylic acid found naturally in ant venom. Explain why me…
- Propanoic acid reacts with sodium carbonate solution. Describe what you would ob…