A 50.0-mL sample of a 0.100 M solution of NaCN is titrated by 0.200 M HCl. Kb

Question:

A 50.0-mL sample of a 0.100 M solution of NaCN is titrated by 0.200 M HCl. Kb for CN is 2.0 × 10-5. Calculate the pH of the solution:
a. Prior to the start of the titration;
b. After the addition of 15.0 mL of 0.100 M HCl;
c. At the equivalence point;
d. After the addition of 30.0 mL of 0.200 M HCl.