What volume of 0.170 M K3PO4(aq) must be added to 50.3 mL of 0.103 M K2HPO4(aq) to prepare a buffer solution with a pH of 12.09?

Answer 1

Use the HH equation.
pH = pK3 + log (50.3*0.103)/(0.170*mL)
Solve for mL.