Question

Write a note on Tollen’s test.

Hint:

Aldehydes are easily distinguished from ketones using Tollen’s test, which forms a silver mirror with aldehydes due to reduction.

Answer 1

Tollen’s test is used to detect the presence of **aldehydes** in a given sample. The reagent used is **Tollen’s reagent**, which is a solution of silver nitrate (AgNO\(_3\)) in aqueous ammonia (NH\(_3\)). Step 1: Reaction with aldehydes.
When an aldehyde is present, it reduces the Tollen’s reagent, resulting in the deposition of **silver mirror** on the inner surface of the test tube. The aldehyde is oxidized to a carboxylic acid in the process: \[ \text{RCHO} + 2[Ag(NH_3)_2]^+ + 3OH^- \rightarrow \text{RCOOH} + 2Ag + 2NH_3 + H_2O \] Here, **RCHO** is the aldehyde group, and **RCOOH** is the corresponding carboxylic acid. The silver ions (Ag\(^+\)) are reduced to metallic silver, which deposits as a mirror.
Step 2: Application.
This test is widely used for the qualitative detection of aldehydes, as ketones do not react with Tollen's reagent. Final Answer: \[ \boxed{\text{Tollen's test detects aldehydes, resulting in the formation of a silver mirror due to reduction of silver ions.}} \]