Propan-1-ol and 1-chloropropane are two organic compounds. Explain how a chemist could distinguish between propan-1-ol and 1-chloropropane using chemical tests, and describe the observations that would confirm the identity of each compound.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A chemist has two unlabelled bottles. One contains propan-1-ol and the other contains 1-chloropropane. Both liquids are colourless and have similar appearances.
Model answer (5 marks)
1. Add a few drops of aqueous silver nitrate, acidified with dilute nitric acid, to each bottle.
2. In the sample containing 1‑chloropropane a white (cream) precipitate of AgCl forms, showing the presence of chloride ions.
3. In the sample containing propan‑1‑ol no precipitate appears, indicating no halide ions.
4. To confirm the alcohol, add a small amount of the sample to a test tube of sodium metal; effervescence of hydrogen gas is observed.
5. The alcohol can also be identified by burning a small piece of the liquid; a clean blue flame is produced.
These observations distinguish propan‑1‑ol (no AgCl, H₂ evolution, blue flame) from 1‑chloropropane (AgCl precipitate).
2. In the sample containing 1‑chloropropane a white (cream) precipitate of AgCl forms, showing the presence of chloride ions.
3. In the sample containing propan‑1‑ol no precipitate appears, indicating no halide ions.
4. To confirm the alcohol, add a small amount of the sample to a test tube of sodium metal; effervescence of hydrogen gas is observed.
5. The alcohol can also be identified by burning a small piece of the liquid; a clean blue flame is produced.
These observations distinguish propan‑1‑ol (no AgCl, H₂ evolution, blue flame) from 1‑chloropropane (AgCl precipitate).
Examiner tips
- Use the silver nitrate test first – a precipitate = halide. Check for hydrogen evolution or blue flame to confirm the alcohol. Mention the halide ion and hydroxyl group to show understanding of series.
Common mistakes
- Failing to acidify the silver nitrate solution. Assuming the blue flame test alone is sufficient without mentioning the halide test. Confusing the colour of the precipitate (white vs cream).
Mark scheme (5 marks)
- Add aqueous silver nitrate (acidified with dilute nitric acid) to each sample / carry out the silver nitrate test for halide ions
- 1-chloropropane produces a white precipitate / cream precipitate with silver nitrate, indicating the presence of chloride ions (halide ions)
- Propan-1-ol produces no precipitate with silver nitrate (no halide ions present)
- Propan-1-ol can be identified by the presence of the hydroxyl (–OH) group / burns with a clean blue flame OR reacts with sodium to produce hydrogen gas / effervescence
- The two compounds belong to different homologous series — propan-1-ol is an alcohol (contains –OH group) and 1-chloropropane is a haloalkane (contains a halogen atom bonded to the carbon chain), which explains the difference in reactivity with silver nitrate
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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