A volume of 25.0 mL of .100 M HCl is titrated against a .100 M NH3 solution added to it from a buret. Calculate the pH value of solution (a) after 10.0 mL of NH3 solution have been added and (b) after 25.0 mL solution have been added (Ka for NH4+ = 5.6 x 10^(-10).)