Suppose you perform a titration of a diprotic acid and you determine the following information: pH at first equivalence point: 4.36 pH at second equivalence point: 8.72 pH at first half-equivalence point: 2.61 pH at second half-equivalence point: 6.09 What is pKa2 for this unknown acid?

Explanation:

It is known that in titration of diprotic acid, pH of the half equivalence points represents of acid.

Therefore, = pH of the second half equivalence point = 6.09

Hence, during the titration of a diiprotic acid () with strong base, the following dissociation take place.

      ( first equivalence point)

    (second equivalence point)

The of diprotic acid will be calculated as follows.

           pH =

Now, at half equivalence point,

Therefore,

        pH =

           pH =

Thus, we can conclude that for this unknown acid is equal to its pH.