Definition: What is Tollens’ Test?
Tollens’ test, also known as a silver-mirror test, is a qualitative laboratory test that is used to differentiate between an aldehyde and a ketone. It uses the fact that aldehydes can be more easily oxidized than ketones. This test cannot distinguish between an aldehyde and an α-hydroxy ketone (e.g., hydroxy acetone) [1-4].
The history of this reaction goes back to 1882 when a work done by German chemist Bernard Tollens was published in a German journal.
Examples of Tollens’ Test
Tollens reagent is a mild oxidizing chemical reagent that is used in the Tollens’ test. It is a colorless, basic, and aqueous solution containing silver ions coordinated to ammonia, forming a diaminesilver(I) complex [Ag(NH3)2]+. Tollens’ reagent is prepared using a two-step procedure. During the process, two events occur. First, the aldehyde gets converted into carbon dioxide. Second, the Ag+ ions are reduced to Ag metal, which leaves a shiny appearance inside the test tube, indicating a positive result [1-3].
Mechanism of Tollens Test 
Q.1. Why does fructose reduce Tollens’ reagent?
Ans. In an aqueous solution, fructose is enolized and converted into aldehyde in a basic medium. As aldehydes generally reduce Tollen’s reagent, thus fructose also reduces Tollen’s reagent.
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