1. Tardigrade
  2. Question
  3. Chemistry
  4. An acidified solution of 0.05 M Zn 2+ is saturated with 0.1 M H 2 S. What is the minimum molar concentration (M) of H +required to prevent the precipitation of ZnS ? Use Ks p( ZnS )=1.25 × 10-22 and overall dissociation constant of H 2 S . K NET =K1 K2=1 × 10-21

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Q. An acidified solution of $0.05 \,M\, Zn ^{2+}$ is saturated with $0.1 \,M \,H _{2} S$. What is the minimum molar concentration $(M)$ of $H ^{+}$required to prevent the precipitation of $ZnS$ ?
Use $K_{s p}( ZnS )=1.25 \times 10^{-22}$ and overall dissociation constant of $H _{2} S . K _{ NET }=K_{1} K_{2}=1 \times 10^{-21}$

JEE AdvancedJEE Advanced 2020

Solution:

$Zn S ( s ) \rightleftharpoons Zn ^{2+}( aq )+ S ^{2}( aq )$
$\left[ S ^{2-}\right]=\frac{ K _{ sp }}{\left[ Zn ^{2+}\right]}=\frac{1.25 \times 10^{-22}}{0.05}=25 \times 10^{-22}$
$ H _{2} S \rightleftharpoons 2 H ^{+}+ S ^{2-} $
$10^{-21}=\frac{\left[ H ^{+}\right]^{2} \times 25 \times 10^{-22}}{0.1} $
${\left[ H ^{+}\right]^{2}=\frac{10^{-22} \times 10^{22}}{25}=\frac{1}{25}} $
${\left[ H ^{+}\right]=\frac{1}{5}=0.20\, M }$