# A forensic scientist is analysing an unknown organic liquid recovered from a crime scene. The liquid is suspected to be either methanol or chloromethane. Describe a chemical test the scientist could carry out to identify which compound is present, including the reagents used, the observations expected for each compound, and what those observations indicate.

> OCR A-Level Chemistry B: Salters (H433) — 4.2 Alcohols, haloalkanes and analysis · Describe · 5 marks

> Methanol is an alcohol. Chloromethane is a haloalkane. Both are colourless liquids at room temperature.

## Mark scheme (5 marks)

1. Add (acidified) silver nitrate solution to the unknown liquid (having first added warm dilute nitric acid / after warming with sodium hydroxide solution for the haloalkane)
2. Chloromethane (haloalkane) produces a white precipitate with silver nitrate solution, indicating the presence of a halide / chloride ion
3. Methanol (alcohol) produces no precipitate / no change with silver nitrate solution
4. Burn / combust a sample and test the combustion products — methanol burns to produce water and carbon dioxide, confirmed by turning cobalt chloride paper pink (water) and turning limewater cloudy (carbon dioxide)
5. Methanol is an alcohol so contains an –OH group, whereas chloromethane is a haloalkane containing a C–Cl bond / halogen atom, which is why the silver nitrate test distinguishes them

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