An aqueous solution contains 0.10 M H_2 S and 0.20 M HCl. If the equilibrium constants for the formation of HS^- from H_2 S is 1.0 × 10^-7 and that…

An aqueous solution contains $\displaystyle 0.10 \mathrm{M} \mathrm{H}_2 \mathrm{~S}$ and $\displaystyle 0.20$ M HCl. If the equilibrium constants for the formation of $\displaystyle \mathrm{HS}^{-}$from $\displaystyle \mathrm{H}_2 \mathrm{~S}$ is $\displaystyle 1.0 \times 10^{-7}$ and that of $\displaystyle \mathrm{S}^{2-}$ from $\displaystyle \mathrm{HS}^{-}$ions is $\displaystyle 1.2 \times 10^{-13}$ then the concentration of $\displaystyle \mathrm{S}^{2-}$ ions in aqueous solution is :