Question

What is tollens test?

Answer 1

It is a test used to determine aldehyde, aromatic aldehyde and alpha hydrox ketone.

Answer 2

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. Tollens’ test uses a reagent known as Tollens’ reagent, which is a colorless, basic, aqueous solution containing silver ions coordinated to ammonia

[Ag(NH³ ) 2+]

[Ag(NH3)2+]

. It is prepared using a two-step procedure.

Step 1: Aqueous silver nitrate is mixed with aqueous sodium hydroxide

AgNO3+NaOH→AgOH+NHO32AgOH→Ag2O+H2

Step 2: Aqueous ammonia is added drop-wise until the precipitated silver oxide completely dissolves

Ag2O+4NH3+H2O→2Ag(NH3)2++2 OH−

Tollens’ reagent oxidizes an aldehyde into the corresponding carboxylic acid.





Ketones are not oxidized by Tollens’ reagent, so the treatment of a ketone with Tollens’ reagent in a glass test tube does not result in a silver mirror