After black and white photographic film has been developed, unreacted silver bromide is removed by reaction with sodium thiosulfate.
$$AgBr+2Na_2S_2O_3\rightarrow 4Na^++Br^-+[Ag(S_2O_3)_2]^{3-}$$
What is the function of the thiosulfate ion?
A
To make the silver ions soluble
B
To oxidise the silver ions
D
To reduce the silver ions
Correct option is A. To make the silver ions soluble
$$AgBr + 2 {Na}_{2}{S}_{2}{O}_{3} \longrightarrow 4 {Na}^{+} + {Br}^{-} + {\left[ Ag {\left( {S}_{2}{O}_{3} \right)}_{2} \right]}^{3-}$$
In the above reaction, thiosulfate ion $$\left( {{S}_{2}{O}_{3}}^{2-} \right)$$ is use to make the silver ion $$\left( {Ag}^{+} \right)$$ soluble.