Question

Calculate $\left[S^{-2}\right]$ in a solution originally having 0.1 M $HCl$ and $0.2M{H}_{2}S$. For $H_{2}S$ $K{a}_1=1.4\times {10}^{-7}$ and $K{a}_2=1.0\times {10}^{-14}$.

• A. $2.8\times {10}^{-22}M$
• B. $3\times {10}^{-15}M$
• C. $2.8\times {10}^{-21}M$
• D. $4\times {10}^{-10}M$

Answer 1

The correct option is A $2.8\times {10}^{-22}M$

Given - $C_1=0.1M{K}_{a1}=1.4\times {10}^{-7}{\alpha }_1=\sqrt{\frac{K_{a1}}{C_1}}=\sqrt{1.4\times {10}^{-6}}$

$C_2=0.2M{K}_{a2}=10\times {10}^{-14}{\alpha }_2=\sqrt{\frac{K_{a2}}{C_2}}=\sqrt{10\times {10}^{-14}}$

$K_1=1.8\times {10}^{-3}$ $K_2=3.1\times {10}^{-7}$

$C=\sqrt{C_1{\alpha }_1+C_2{\alpha }_2}$

$C^2=2.8\times {10}^{-22}$