The dissociation constant of `H_(2)S` and `HS^(-)` are respectively `10^(-7)` and `10^(-13)` . The pH of 0.1 M aqueous solution of `H_(2)S` will be

Options

A. 4
B. 3
C. 5
D. 2.5

Answer

A

Explanation

Since `K_(a2) lt lt lt K_(a1)` Thus, `H^(+)` ions are mainly obtained from the first step i.e.,
`H_(2)S hArr HS^(-) +H^(+)`
`:. [H^(+)] =sqrt(KC)=sqrt(10^(-7) xx10^(-1))=10^(-4)`
`:. pH =-log (10^(-4))=4`