Answer to Question #14722 in Chemistry for John

Question

It is your first day of work in your new laboratory job. You are asked to prepare 700 mL of PBS (phosphate buffered saline). The PBS needs to be pH 7.40, with 25 mM phosphate and 140 mM NaCl. You are given a bottle of NaCl (FW = 58.45), a 1.00 M Na2HPO4 stock solution, and a 1.00 M NaH2PO4 stock solution. Describe how to prepare this buffer. (For H3PO4: pK1 = 2.12, pK2 = 7.21, pK3 = 12.66)