Tollens' reagent

This reagent is not commercially available due to its short shelf life, so it must be freshly prepared in the laboratory.

First a few drops of dilute sodium hydroxide are added to some aqueous 0.1 M silver nitrate.

The resulting solution contains the [Ag(NH3)2]+ complexes in the mixture, which is the main component of Tollens' reagent.

Sodium hydroxide is reformed: Alternatively, aqueous ammonia can be added directly to silver nitrate solution.

[2] At first, ammonia will induce formation of solid silver oxide, but with additional ammonia, this solid precipitate dissolves to give a clear solution of diamminesilver(I) coordination complex,

The diamine silver(I) complex in the mixture is an oxidizing agent and is the essential reactant in Tollens' reagent.

Another test relies on reaction of the furfural with phloroglucinol to produce a colored compound with high molar absorptivity.

[4] It also gives a positive test with hydrazines, hydrazones, α-hydroxy ketones and 1,2-dicarbonyls.

[citation needed] In anatomic pathology, ammonical silver nitrate is used in the Fontana–Masson Stain, which is a silver stain technique used to detect melanin, argentaffin and lipofuscin in tissue sections.

[2] Tollens' reagent is also used to apply a silver mirror to glassware; for example the inside of an insulated vacuum flask.

To increase the speed of deposition, the glass surface may be pre-treated with tin(II) chloride stabilised in hydrochloric acid solution.

[5] For applications requiring the highest optical quality, such as in telescope mirrors, the use of tin(II) chloride is problematic, since it creates nanoscale roughness and reduces the reflectivity.

[6][7] Methods to produce telescope mirrors include additional additives to increase adhesion and film resilience, such as in Martin's method, which includes tartaric acid and ethanol.

[7] Aged reagent can be destroyed with dilute acid to prevent the formation of the highly explosive silver nitride.