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Question

Chemistry Question on d -and f -Block Elements

Hypo is used in photography to

A

reduce AgBr grains to metallic silver

B

convert metallic silver to silver salt

C

remove undecomposed silver bromide as a soluble complex

D

remove reduced silver

Answer

remove undecomposed silver bromide as a soluble complex

Explanation

Solution

After the developing, the sensitive emulsion of
silver bromide is still present on the plate in the
parts unaffected by light. Therefore, it is necessary
to remove it in order to get the permanent image.
This process is called fixing of image. The negative
plate after washing is dipped in a fixing solution of
sodium thiosulphate (hypo). It dissolves unaffected
silver bromide but leaves metallic silver unaffected.
2Na2S2O3+AgBrNa3[Ag(S2O3)2]+NaBr2Na_2S_2O_3 + AgBr\longrightarrow Na_3[Ag(S_2O_3)_2] + NaBr