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6-2.Equilibrium-II (Ionic Equilibrium)
easy
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 $K_{ sp }( ZnS )=1.25 \times 10^{-22}$ and
Overall dissociation constant of $H _2 S , K_{ NET }=K_1 K_2=1 \times 10^{-21}$
A
$0.10$
B
$0.15$
C
$0.20$
D
$0.25$
(IIT-2020)
Solution
For ppt , $\quad\left[ Zn ^{+2}\right]\left[ S ^{-2}\right]= K _{ sp }$
$\begin{array}{l}{\left[ S ^{-2}\right]=\frac{1.25 \times 10^{-22}}{0.05}} \\ =2.5 \times 10^{-21} M \end{array}$
$H _2 S \rightleftharpoons 2 H ^{+}+ S ^{-2}$
$K _{\text {Net }}=10^{-21}=\frac{\left[ H ^{+}\right]^2 \times 2.5 \times 10^{-21}}{0.1}$
${\left[ H ^{+}\right]^2=\frac{1}{25}}$
${\left[ H ^{+}\right]=\frac{1}{5} M =0.2 M }$
Standard 11
Chemistry
