Buffer Solution Chemistry Math Question 2

Question

Benzoic acid is used to titrate an unknown base, and the pH of solution is recorded during the titration. Halfway to the ultimate endpoint of the titration, the pH of solution was recorded at 9.26. What is the value of K_b for the unknown base?

Answer 1

The question doesn't state whether the unknown base is strong or weak, but since it is asking for the Kb, we can assume it to be a weak base. There are other problems with this question as well.

a) The ultimate "endpoint" is not the same as the equivalence point, and without knowing the indicator and accuracy of the "endpoint", one cannot predict much about the titration.

b) Neither the Ka nor pKa for benzoic acid is provided and this will be needed in any calculation that may ensue.

c) Titration of a weak base with a weak acid is fraught with difficulties and is hardly ever performed in practice.

So, without further information, or at least some clarification, I'm reluctant to post an answer to such a query.