Silver Ammonia
Silver ammonia, also known as Tollens' reagent or silver mirror test, is a chemical test used to identify the presence of aldehydes in a given sample. It consists of a solution of silver nitrate (AgNO3) and ammonia (NH3) in water.
When an aldehyde is added to the silver ammonia solution, it reduces the silver ions (Ag+) to metallic silver (Ag), which forms a silver mirror on the surface of the container. The reduction reaction occurs in two steps:
1. The aldehyde is oxidized to a carboxylic acid by the silver ion, which is reduced to metallic silver:
RCHO + 2Ag(NH3)2+ + 3OH- → RCOO- + Ag2O(s) + 4NH3 + 2H2O
2. The silver oxide produced in the first step reacts with excess silver ions to form metallic silver, which precipitates out of solution and forms a mirror:
Ag2O + 2Ag(NH3)2+ + H2O → 4Ag + 4NH3 + 2OH-
The silver mirror test is a qualitative test, meaning that it can only indicate the presence or absence of an aldehyde, not its concentration or identity. It is commonly used in organic chemistry as a quick and simple way to identify aldehydes, but it may also react with other reducing agents such as ketones or some sugars.