Question

$N{a}_2{S}_2{O}_3.5H_{2}O$ is used in photography to

• A. reduce AgBr to metallic Ag
• B. remove reduced Ag
• C. remove undecomposed AgBr as a soluble complex
• D. convert metallic Ag to silver salt

Answer 1

Answer: (C)

$N{a}_2{S}_2{O}_3.5H_{2}O$ is used in photography to remove undecomposed AgBr as a soluble complex as:
$\text{AgBr}+2{\left(\text{Na}\right)}_2{\left(\text{S}\right)}_2{\left(\text{O}\right)}_3\to \underset{\text{Soluble complex}}{{\left(\text{Na}\right)}_3[\text{Ag}{\left(\text{S}\right)}_2{\left(\text{O}\right)}_3\left({)}_2\right]}+\text{NaBr}$
Sodium thiosulfate is used by photographers to fix developed negatives and prints; it acts by dissolving the part of the silver salts coated onto film which remain unchanged by exposure to light.