Question

For testing thiosulphate solution if we use Mercuric nitrate as reagent then :

• A. We get brown precipitate of mercuric thiosulphate.
• B. The compound formed is thermally unstable.
• C. The precipitate formed is soluble in excess of thiosulphate.
• D. On heating the precipitate formed we see the colour transition from white to black precipitate.

Answer 1

Answer: (B), (C), (D)

The correct options are
B The compound formed is thermally unstable.
C The precipitate formed is soluble in excess of thiosulphate.
D On heating the precipitate formed we see the colour transition from white to black precipitate.

When silver nitrate is added in sodium thiosulphate, a white ppt of silver thiosulphate is formed. This silver thiosulphate disproportionates to give silver sulphide and sulphuric acid, silver sulphide is black. That is, on adding mercuric nitrate a black precipitate is obtained which changes to brown and finally to black.Furthermore, in the presence of excess of thiosulphate ions the ppt of Silver thiosulphate dissolves giving a colorless complex.