How are complex compounds applicable in (a) electroplating of silver, gold or other noble metals (b) in photography

Dear Student,

(a) Electroplating is the application of a metal coating to a metallic or other conducting surface by an electrochemical process. ​Cyanide complexes are used here. There are two main purpose of forming complex ions of certain cations:

1. To stabilise the ​cation. Some metal cations are not stable in the simple aquated form, e.g. gold. They are much more stable when complexed to some ligand. The presence of the ligand lowers the concentration of the free (aquated) ion.
2. To hold the aquated form at suitably low concentration allowing control of the evenness of plating.

(b) A complex of silver and thiosulphate ion [Ag(S₂O₃)₂]^3- forms the basis of fixing process in photography.