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%` ionised, so [Salt] = [Acid]
`pH = 4.5`
`pH+pOH=14`
`:. pOH= 14-4.5 = 9.5`