In black-and-white photography, unexposed silver bromide () is dissolved by washing the film with a sodium thiosulphate (hypo) solution, forming a highly water-soluble complex. Exactly how many thiosu

Question

In black-and-white photography, unexposed silver bromide ($AgBr$) is dissolved by washing the film with a sodium thiosulphate (hypo) solution, forming a highly water-soluble complex. Exactly how many thiosulphate ($S_2O_3^{2-}$) ligands are directly coordinated to the central Silver ($Ag^+$) cation in this stable transition metal complex?

Prashant Kotian · Accepted Answer

Correct answer: 2. The fixing process relies on the formation of a highly stable, water-soluble coordination complex between the transition metal silver and the thiosulphate ligands. The balanced reaction is: . In the resulting complex, Sodium dithiosulphatoargentate(I), the central cation is coordinated directly to exactly thiosulphate ligands.

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