The `pK_(a)` of a weak acid `(HA)` is `4.5`. The `pOH` of an aqueous buffered solution of `HA` in which `50%` of the acid is ionized is:

Options

A. `4.5`
B. `2.5`
C. `9.5`
D. `7.0`

Answer

C

Explanation

For buffer solution
`pH=pK_(a)+log.(["Salt"])/(["Acid"])=4.5+log.(["Salt"])/(["Acid"])`
as HA is `50%` ionized so [Salt]=[Acid]
`pH=4.5`
`pH+pOH=14`
`impliespOH=14-4.5=9.5`