An 80.0-mL sample of 0.200 M ammonia is titrated with 0.100 M hydrochloric acid. Kb for ammonia is 1.8 × 10-5. Calculate the pH of the solution at each of the following points of the titration:
a. Before the addition of any HCl;
b. Halfway to the equivalence point;
c. At the equivalence point;
d. After the addition of 175 mL of 0.100 M HCl.