Question: how to get pkb from pka?
Answer: After you have determined the equivalence point (endpoint) of the titration, go to half that value. The pH at the half-titration point is equal to the pKa of the weak acid, BH+. To get the pKb of the base (B) you MUST subtract the pKa from 14. The reason for this is that the pOH is actually what equals the pKb.