A student wants to produce ethyl ethanoate, an ester, starting from ethanol and ethanoic acid. Describe how the student would carry out this reaction in the laboratory, and explain how the ester could be separated from the reaction mixture.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Esters can be made by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst. The reaction is reversible and the yield of ester is relatively low.
Model answer (5 marks)
1. Mix ethanol and ethanoic acid in a round‑bottom flask.
2. Add a few drops of concentrated sulphuric acid as catalyst.
3. Heat the mixture gently under reflux (or in a water bath) to drive the esterification.
4. After cooling, add a sodium carbonate solution to neutralise the acid catalyst and remove any excess ethanoic acid.
5. Transfer the mixture to a separating funnel; the ethyl ethanoate forms a separate, immiscible layer which is then collected.
2. Add a few drops of concentrated sulphuric acid as catalyst.
3. Heat the mixture gently under reflux (or in a water bath) to drive the esterification.
4. After cooling, add a sodium carbonate solution to neutralise the acid catalyst and remove any excess ethanoic acid.
5. Transfer the mixture to a separating funnel; the ethyl ethanoate forms a separate, immiscible layer which is then collected.
Examiner tips
- Use the exact terms: sulphuric acid, reflux, sodium carbonate, separating funnel. Show the step of neutralising the acid before separation. Mention the immiscibility of the ester with water.
- common_mistakes
- :
- Omitting the neutralisation step with sodium carbonate. Using a non‑specific heating method (e.g., just “heat” without specifying reflux or water bath). Failing to state that the ester layer is immiscible with water.
Mark scheme (5 marks)
- Concentrated sulfuric acid is used as the acid catalyst
- The mixture is heated (gently / under reflux / in a water bath)
- Sodium carbonate (solution) is added to the mixture to neutralise / remove the acid catalyst and unreacted ethanoic acid
- The ester separates as a distinct layer (because it is immiscible with / insoluble in water)
- The ester layer is separated using a separating funnel
Key terms in this question
Related
- All WJEC A-Level Chemistry (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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