Demonstration of Tollens' Reagent

In this demonstration, an aldehyde is tested using Tollen's reagent. In this test, the presence of an aldehyde is confirmed by the appearance of a 'silver mirror'.

This test is commonly used to differentiate between the two types of carbonyl compound: aldehydes and ketones. Unlike ketones, aldehydes can be oxidised to carboxylic acids. This enables aldehydes to behave as reducing agents. In this demonstration, the aldehyde reduces the silver(I) ions in ammoniacal silver nitrate solution to form solid silver. This reaction results in the appearance of a silver mirror.

This is quite a difficult test to perform: the mixing of the chemicals needs to be quite accurate, as does the degree of heating. Brand new test tubes are recommended.