Calculate the pH for each of the cases in the titration of 25.0 mL of 0.200 M pyridine, C5H5N(aq) with 0.200 M HBr(aq). The b of pyridine is 1.7×10−9.

Before addition of any HBr


after addition of 12.5 mL of HBr


after addition of 18.0 mL of HBrHBr


after addition of 25.0 mL of HBr HBr


after addition of 30.0 mL of HBr HBr

Some explanation of the reasoning for the setup of the first two steps would be appreciated. Thank you.