Tollens' reagent
Tollens' reagent is usually ammoniacal silver nitrate, but can also be other things, as long as there is an aqueous diammide silver complex.
Uses
The diammide silver complex is an oxidising agent, which is itself reduced to silver metal, which in a clean glass reaction vessel forms a 'silver mirror'. This feature is used as a test for aldehydes, which are oxidised to carboxylic acids.
Once it has been identified that there is a carbonyl group on the organic molecule using 2,4-dinitrophenylhydrazine (also known as Brady's reagent), Tollens' reagent can be used to ascertain whether the compound is a ketone or an aldehyde.
Laboratory Preparation
- To aqueous silver nitrate, add either dilute sodium hydroxide or ammonia until the precipitate that forms just dissolves.
- This is ammoniacal silver nitrate, [Ag(NH3)2]NO3 (aq).