Question

When $H_{2}S$ gas is passed through a hot acidic aqueous solution containing $A{l}^{3+},C{u}^{2+},P{b}^{2+}andN{i}^{2+}$, a precipitate is formed which consists of

• A.
• B.
• C.
• D.

Answer 1

The correct option is D

$A{g}^{+},P{b}^{2+}andH{g}^{2+}$ cations produce insoluble chlorides so they can be precipitated with dilute HCl, while all other cations remain in solution.
$C{u}^{2+},B{i}^{3+},C{d}^{2+},H{g}^{2+},A{s}^{3+},S{b}^{3+}andS{n}^{4+}$ cations produce very insoluble sulfides (Ksp values less than 10-30) so they can be precipitated by low amounts of sulfide ion; this can be achieved by adding an acidic solution of $H_{2}S$.
$A{l}^{3+},C{r}^{3+},F{e}^{3+},Z{n}^{2+},N{i}^{2+},C{o}^{2+}andM{n}^{2+}$ cations produce slightly soluble sulfides (Ksp values more than 10-20) so they can be precipitated by relatively high amounts of sulfide ion; this can be achieved by adding a basic solution of $H_{2}S$.
So, the precipitate formed is of $PbSandCuS$