Propan-1-ol can be converted into 1-chloropropane, a haloalkane, in a substitution reaction. Explain how the functional groups in propan-1-ol and 1-chloropropane differ, and describe how a chemist could use a chemical test to confirm that the product formed is a haloalkane and not an alcohol.

OCR A-Level Chemistry A (H432) — 4.2 Alcohols, haloalkanes and analysis · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Propan-1-ol (CH₃CH₂CH₂OH) reacts with phosphorus pentachloride to produce 1-chloropropane (CH₃CH₂CH₂Cl), hydrogen chloride gas and phosphorus oxychloride. The chemist needs to confirm that the reaction has produced a haloalkane.

Model answer (5 marks)

1. Propan‑1‑ol contains a hydroxyl –OH functional group.
2. 1‑Chloropropane contains a chlorine atom bonded to carbon (C–Cl) as its functional group.
3. The –OH group is polar and can donate hydrogen bonds, whereas C–Cl is a polar covalent bond but not a hydrogen‑bond donor.
4. To test the product, dissolve a small sample in ethanol or water and add a few drops of acidified silver nitrate solution.
5. 1‑Chloropropane gives a white/cream precipitate of AgCl, whereas propan‑1‑ol shows no precipitate, confirming the product is a haloalkane.

Examiner tips

  • Use the command word ‘explain’ – give clear, concise points. Show the functional‑group difference before describing the test. Mention the solvent (ethanol or water) and acidified AgNO₃. State the expected result for each compound.
  • common_mistakes
  • :
  • Confusing the precipitate with a colour change of the solution. Forgetting to specify the solvent or that the AgNO₃ is acidified. Describing the test but not linking the result to the functional group difference.

Mark scheme (5 marks)

  1. Propan-1-ol contains an –OH (hydroxyl) functional group
  2. 1-Chloropropane contains a halogen atom (chlorine / C–Cl) as its functional group instead of –OH
  3. Add acidified silver nitrate solution to both compounds (after dissolving in ethanol / water)
  4. The haloalkane (1-chloropropane) produces a white / cream precipitate of silver chloride
  5. The alcohol (propan-1-ol) gives no precipitate / no change with silver nitrate solution, confirming it is not the haloalkane

Key terms in this question

haloalkane · alcohol · functional group

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