Question

Why only $As ^{3+}$ gets precipitated as $As _{2} S _{3}$ and not $Zn ^{2+}$ as $ZnS$ when $H _{2} S$ is passed through an acidic solution containing $A s^{3+}$ and $Zn ^{2+} ?$

• A. Solubility product of $As _{2} S _{3}$ is less than that of $ZnS$
• B. Enough $As ^{3+}$ are present in acidic medium
• C. Zinc salt does not ionise in acidic medium
• D. Solubility product changes in presence of an acid

Answer 1

Answer: (A)

$K _{ sp }$ of $As _{2} S _{3}$ is less than $ZnS$. In acid medium ionisation of $H _{2} S$ is suppresed (common ion effect) and $K _{ sp }$ of $ZnS$ does not exceed.