Calculate the pH for each of the cases in the titration of 25.0 mL of 0.200 M pyridine, C5HN(aq) with 0.200 M HBr(aq). The b of pyridine is 1.7×10−9.

(a). Before addition of any HBr:

(b). after addition of 12.5 mL of HBr:

(c). after addition of 18.0 mL of HBr:
after addition of 25.0 mL of HBr HBr, after addition of 30.0 mL of HBr HBr
with explanation of all steps.