Answer to Question #144431 in General Chemistry for martha

Question

describe how you would prepare a buffer solution from NaH2PO4 and Na2HPO4 to have a pH of 7.5.

Answer 1

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