A certain buffer solution contains equal concentartion of `X^(Theta)` and `HX`. The `K_(b)` for `X^(Theta)` 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 `