Question

Hypo is used in photography to

• A. reduce $\text{AgBr}$ grains to metallic silver
• B. convert the metallic silver to silver salt
• C. remove undecomposed silver bromide as a soluble complex
• D. remove reduced silver

Answer 1

Answer: (C)

Hypo or sodium thiosulphate $(N{a}_2{S}_2{O}_3.5H_{2}O)$ is used in photography to remove undecomposed silver bromide, which is soluble in hypo and forms a complex salt. $\underset{\begin{array}{c}silver\\ bromide\end{array}}{\mathrm{AgBr}}+\underset{hypo}{2N{a}_2{S}_2{O}_3}\to \underset{\begin{array}{c}\text{sodium}\text{argento}\\ \text{thiosulphate}\end{array}}{N{a}_3[Ag{(S_2{O}_3)}_2]}$ $+NaBr$