Question #144431
describe how you would prepare a buffer solution from NaH2PO4 and Na2HPO4 to have a pH of 7.5.
Expert's answer
Sodium phosphate buffer (0.2 M)
MATERIALS
Reagents
Na2HPO4•2H2O
NaH2PO4•H2O
METHOD
1. Dissolve 35.61 g of Na2HPO4•2H2O and 27.6 g of NaH2PO4•H2O separately in H2O.
2. Adjust the volume of each solution to 1000 mL.
Store the stock solutions for up to 6 mo at 4°C.
3. To prepare the buffer, mix the stock solutions as follows:
《A》 . For 50 mL: 38.5 mL of Na2HPO4•2H2O and 11.5 mL of NaH2PO4•H2O.
《B》.For 100 mL: 77 mL of Na2HPO4•2H2O and 23 mL of NaH2PO4•H2O.
《C》.For 500 mL: 385 mL of Na2HPO4•2H2O and 115 mL of NaH2PO4•H2O.
《D》.For 1000 mL: 770 mL of Na2HPO4•2H2O and 230 mL of NaH2PO4•H2O.
4. Check the pH of the solution at room temperature. If necessary, adjust the pH to 7.5
