Tollens' reagent, also known as Tollen's reagent or Tildon reagent, is a chemical reagent that is commonly used to distinguish between aldehydes and ketones. It is named after the German chemist Bernhard Tollens, who developed the reagent in the late 19th century.

Composition of Tollen's reagent:
Tollens' reagent is composed of two main components: silver nitrate (AgNO3) and ammonia (NH3). Silver nitrate is the oxidizing agent, while ammonia acts as a complexing agent.

Preparation of Tollen's reagent:
Tollen's reagent is prepared by mixing a solution of silver nitrate with an equal volume of ammonia. The resulting mixture is alkaline in nature and contains silver(I) ions (Ag+).

Reaction with aldehydes:
When Tollens' reagent is added to an aldehyde, such as formaldehyde or acetaldehyde, a redox reaction occurs. The aldehyde is oxidized to a carboxylic acid, while the silver(I) ions are reduced to metallic silver. This reaction forms a silver mirror on the inner surface of the reaction vessel.

Reaction with ketones:
Ketones do not react with Tollens' reagent under normal conditions. Unlike aldehydes, ketones do not have an active hydrogen atom that can be oxidized. Therefore, the absence of a silver mirror indicates the presence of a ketone.

Limitations of Tollen's reagent:
While Tollens' reagent is a useful test for distinguishing aldehydes from ketones, it has some limitations:

1. It cannot differentiate between different aldehydes or ketones.
2. It requires the presence of an alpha-hydrogen in the aldehyde for the oxidation to occur.
3. Some compounds, such as alcohols and acids, can also react with Tollens' reagent, leading to false-positive results.

Applications of Tollen's reagent:
Tollen's reagent is commonly used in organic chemistry laboratories as a qualitative test for the presence of aldehydes. It can be used to identify aldehydes in various organic compounds, such as aldehydic sugars, aldehydes in essential oils, or aldehydes formed during the oxidation of alcohols.

In conclusion, Tollens' reagent is a chemical reagent used to distinguish between aldehydes and ketones. It is prepared by mixing silver nitrate and ammonia. Aldehydes are oxidized to carboxylic acids, producing a silver mirror, while ketones do not react with the reagent. However, it is important to note the limitations and potential false-positive results when using Tollens' reagent.