As a technician in a large pharmaceutical research firm, you need to produce 400 mL of 1.00 M potassium phosphate buffer solution of pH = 7.29. The pKa of H_2PO_4^- is 7.21.
You have the following supplies: 2.00 L of 1.00 M KH_2PO_4 stock solution, 1.50 L of 1.00 M K_2HPO_4 stock solution, and a carboy of pure distilled H_2O.
How much 1.00 M KH_2PO_4 will you need to make this solution?