Compute the pH at the halfway point and at the equivalence point for each of the following titrations.
a. 100.0 ml of 0.10 M HC7H5O2 (Ka = 6-4x10^-5) titrated by 0.10 M NaOH
b. 100.0 ml of 0.10 M C2H5NH2 (Kb= 5.6x10^-4) titrated by 0.20 M HNO3
c. 100.0 ml of 0.50 M HCL titrated by 0.25 M NaOH