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`
`:. pOH=14-4.5=9.5`