100.0mL of a K2HPO4 solution is titrated with 0.1187M NaOH. The endpoint is reached when 115.4mL of OH- has been added. Find out the mass of K2HPO4 dissolved in the original 100.0 mL H2O as well as the pH of the solution at the end point of the titration.
H3PO4 (aq) + H20 <-> H2PO-4 (aq) +H3O (aq) Ka1=7.11x10^-3
H2PO4- (aq) + H2O <-> HPO2-4 (aq) + H3O+ (aq) Ka2=6.34x10^-8
HPO2- 4 (aq) +H2O <-> PO3- 4 (aq) + H3O+ (aq) Ka3=4.22x10^-13