When the soda extract containing thiosulphate ion is treated with excess of `AgNO_(3)` solution followed by boiling, then:

Options

A. white precipitate is formed
B. black precipitate is formed
C. brown precipitate is formed
D. no ppt precipitate is formed

Answer

B

Explanation

`S_(2)O_(3)^(2-)+2Ag^(+) rarr underset(("White"))(Ag_(2)S_(2)O_(3))darr`.
At first, no ppt occurs because:
`2S_(2)O_(3)^(2-) +Ag^(+) rarr [Ag(S_(2)O_(3))_(2)]^(3-)`
`Ag_(2)S_(2)O_(3)` turns dark on standing:
`Ag_(2)S_(2)O_(3)darr +H_(2)O rarr Ag_(2)S darr +2H^(+)+SO_(4)^(2-)`