Tollens' reagent is an alkaline solution of ammoniacal silver nitrate and is used to test for aldehydes. Silver ions in the presence of hydroxide ions come out of the solution as a brown precipitate of silver(I) oxide, . This precipitate dissolves in aqueous ammonia, forming the diamminesilver(I) ion, .
The sodium bisulphite test is used to detect aldehydes and methyl ketones.
Aldehydes and methyl ketones react with sodium bisulphite ( ) to form bisulphite addition compounds, which are crystalline solids.
These crystalline derivatives are useful for characterization and purification of aldehydes and some ketones.
Other alcohols or non-methyl ketones generally do not give this test.

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