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
`rArr pOH = 14 - 4.5 = 9.5`.