A certain buffer solution contains equal concentration of `X^-` and HX. The `K_b` for `X^-` is `10^-10`. The pH of the buffer is:

Options

A. 4
B. 7
C. 10
D. 14

Answer

A

Explanation

`X^(-) + H_(2)O hArr OH^(-) + HX`
`K_(b) = ([OH^(-)][HX])/([X^(-)])`
`HX hArr H^(+) + X^(-)`
`K_(a) = ([H^(+)][X^(-)])/([HX]), :. K_(a) xx K_(b) = [H^(+)][OH^(-)] = K_(w) = 10^(-14)`
Hence `K_(a) = 10^(-4)`
Now as `[X^(-)] = [HX], pH = pK_(a) = 4`.