what is the pH half-way to the stoichiometric point ?

Question

107.0 mL of a solution of quinine contains 214.0 x 10-3 mol of quinine.
If this is titrated with 0.200 M HCl, what is the pH half-way to the stoichiometric point ?

Quinine is monobasic with Kb = 7.90 x 10-6

I know the steps to take but my answer is not coming out right

Answer 1

The pH half way is 14-pKb

pKb

= log 1/7.910^-6 =-5.1

so 14-5.1 =8.9 =pH

Remember for an acid at half-neutralization pH = Pka

fro a base , same calculus , you find pKb and see the formula


here there was 0.107* 0.214 =0.0229 moles of Quinine

as the solution contained 0.200 mole/l you need =0.114l o0.2m HCl