AgNO3+NaOH→AgOH+NaNO3
2AgOH→Ag2O+H2O
Ag2O+4NH3+H2O→2Ag(NH3)2++2O⊝H

Tollens' reagent is an alkaline solution of ammoniacal silver nitrate and is used to test for aldehydes. Tollens' test, also known as silver-mirror test, is a qualitative laboratory test used to distinguish between an aldehyde and a ketone. It exploits the fact that aldehydes are readily oxidized (see oxidation), whereas ketones are not.