Question

Three separate samples of a solution of a single salt gave these results. One formed a white precipitate with excess ammonia solution, one formed a white precipitate with dil. $HCl$ solution and one formed a black precipitate with $H_{2} S$. The salt could be

• A. $AgNO_3$
• B. $Pb(NO_3)_2$
• C. $Hg(NO_3)_2$
• D. $MnSO_4$

Answer 1

Answer: (B)

$Pb(NO_3)_2$

Answer 2

The salt could be $Pb \left( NO _{3}\right)_{2}$
It formed a white precipitate with excess ammonia solution:
$Pb \left( NO _{3}\right)_{2}+2 NH _{4} OH \rightarrow Pb ( OH )_{2} \downarrow$ (white ppt) $+2 NH _{4} NO _{3}$
It formed a white precipitate with dil. $NaCl$ solution:
$Pb \left( NO _{3}\right)_{2}+2 NaCl \rightarrow PbCl _{2} \downarrow$ (white ppt) $+2 NaNO _{3}$
It formed a black precipitate with $H _{2} S$ :
$Pb \left( NO _{3}\right)_{2}+ H 2 S \rightarrow PbS \downarrow$ (black ppt) $+2 HNO _{3}$