A chemist wants to make a pure, dry sample of the organic compound propan-1-ol starting from propene. Outline the steps the chemist should carry out, including any reagents and conditions needed, to obtain a pure, dry sample of propan-1-ol.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Propene is an alkene that can be converted into propan-1-ol by reacting it with steam in the presence of an acid catalyst. The product mixture may contain unreacted propene gas, water, and traces of acid.
Model answer (5 marks)
1. React propene with steam in the presence of an acid catalyst (e.g. H₃PO₄) to give propan‑1‑ol.
2. Condense the gaseous product to obtain a liquid mixture of propan‑1‑ol, water and unreacted propene.
3. Add a suitable base such as sodium carbonate or sodium hydroxide solution to neutralise the acid catalyst and remove it from the mixture.
4. Add a drying agent (e.g. anhydrous calcium chloride or anhydrous magnesium sulfate) to remove water from the liquid.
5. Distil the dried liquid and collect the fraction boiling at 97 °C to give pure, dry propan‑1‑ol.
2. Condense the gaseous product to obtain a liquid mixture of propan‑1‑ol, water and unreacted propene.
3. Add a suitable base such as sodium carbonate or sodium hydroxide solution to neutralise the acid catalyst and remove it from the mixture.
4. Add a drying agent (e.g. anhydrous calcium chloride or anhydrous magnesium sulfate) to remove water from the liquid.
5. Distil the dried liquid and collect the fraction boiling at 97 °C to give pure, dry propan‑1‑ol.
Examiner tips
- Use the exact wording ‘react propene with steam in the presence of an acid catalyst’ to gain the first point. Show the neutralisation step with a base and the drying agent before distillation. Mention the boiling point of propan‑1‑ol (97 °C) when describing the distillation step.
- Include the catalyst name (H₃PO₄) and the drying agent in the answer – examiners look for specific reagents.
Mark scheme (5 marks)
- React propene with steam (water) in the presence of an acid catalyst / phosphoric acid catalyst / H₃PO₄
- Collect / condense the gaseous product to obtain the liquid propan-1-ol mixture
- Add a suitable base / sodium carbonate / sodium hydroxide solution to neutralise / remove the acid catalyst from the product
- Add a drying agent (e.g. anhydrous calcium chloride / anhydrous magnesium sulfate) to remove water
- Distil the dried liquid and collect the fraction at the boiling point of propan-1-ol (97 °C) to obtain the pure product
Related
- All WJEC A-Level Chemistry (Wales) revision notes →
- How to answer a "Outline" question →
- Decode the mark scheme abbreviations →
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