An aqueous solution of a metal bromide `MBr_(2)(0.05M)` is saturated with `H_(2)S`. What is the minimum pH at which MS will precipitate ? `K_(SP)` for `M S= 6.0xx10^(-21)` . Concentration of saturqated `H_(2)S=0.1M, K_(1)=10^(-7)and K_(2)=1.3xx10^(-13)` for `H_(2)S` .

Options

A. `pH=1.6`
B. `pH=0.67`
C. `pH=0.98`
D. `pH=0.771`

Answer

C

Explanation

`K=K_(1)K_(2)=([H^(+)]^(2)[S^(2-)])/([H_(2)S])=10^(-7)x1.3x10^(-13)`
`([H^(+)]^(2)[S^(2-)])/([H_(2)S])=([H^(+)]^(2)x1.2x10^(-19))/(0.1)=1.3x10^(-30)`
`[H^(+)]= sqrt(1.083x10^(-2))=0.104M= pH=0.98`