During the titration of a weak diprotic acid `(H_(2)A)` against a strong base `(NaOH)`, the pH of the solution half-way to the first equivalent point and that at the first equivalent point are given respectively by:

Options

A. `pK_(a_(1))` and `pK_(a_(1)) + pK_(a_(2))`
B. `sqrt(K_(a_(1))c)` and `(pK_(a_(1)) + pK_(a_(2)))/(2)`
C. `pK_(a_(1))` and `(pK_(a_(1)) + pK_(a_(2)))/(2)`
D. `pK_(a_(1))` and `pK_(a_(2))`

Answer

C

Explanation

Half of `1st ` equivalence point `rArr` Buffer exists
`pH = pKa_(1) + "log" ([S])/([A])`
`[S] = [A] rArr pH = pKa_(1)`
At `1st` equivalence point
`rArr (pKa_(1) + pKa_(2))/(2)`