Which of the following compounds gives white precipitate turning to brown and ultimately black when treated…

Which of the following compounds gives white precipitate turning to brown and ultimately black when treated with silver nitrate solution?
  1. $\mathrm{KNO}_{3}$
  2. $\mathrm{K}_{2} \mathrm{SO}_{4}$
  3. $\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$
  4. $\mathrm{Na}_{2} \mathrm{SO}_{3}$

Solution

On reaction of a hyposolution i.e. sodium thiosulphate with silver nitrate, silver thiosulphate is formed that goes through a colour change i.e. from white ppt to black ppt
$\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}+2 \mathrm{AgNO}_{3} ightarrow \mathrm{Ag}_{2} \mathrm{S}_{2} \mathrm{O}_{3}+2 \mathrm{NaNO}_{3}$
$\mathrm{Ag}_{2} \mathrm{NO}_{3}+\mathrm{H}_{2} \mathrm{O} ightarrow \mathrm{Ag}_{2} \mathrm{S}+\mathrm{H}_{2} \mathrm{SO}_{4}$ .

Asked in: JEE-TOPICTESTS-CHEMISTRY

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