Add one drop or a few crystals of unknown to the freshly prepared Tollens reagent. Gentle heating can be employed if no reaction is immediately observed.
Tollens reagent: Into a test tube which has been cleaned with 10% sodium hydroxide, place 2 mL of a 5% silver nitrate solution, and add a drop of 10% sodium hydroxide. Add 2% ammonia solution, drop by drop, with constant shaking, until the precipitate of silver oxide just dissolves.
Formation of silver mirror or black precipitate is a positive test.
The test tube must be clean and free of oil if a silver mirror is to be observed.
Easily oxidized compounds give a positive test. For example: aromatic amine, some phenols, a-alkoxy and a-dialkylaminoketones.
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