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 `1.0xx10^(–7)` and that of `S^(2-)` from `HS^(–)` ions is `1.2xx10^(–13)` then the concentration of `S^(2-)` ions in aqueous solution is

Options

A. `3xx10^(-20)`
B. `6xx10^(-21)`
C. `5xx10^(-19)`
D. `5xx10^(-8)`

Answer

A

Explanation

`{:(HCl to, H^(+),+, CI^(-)),(,(0.2+x+y),,0.2):}`
`{:(H_(2)ShArrH^(+),+, HS^(-):Ka_(1)=10^(-7)),(0.1-x(0.2+x+y),,(x-y)),(HS^(-)hArrH^(+),+,S^(2-):K_(a_(2))=1.2xx10^(-13)):}`