Answer to Question #307045 in Physical Chemistry for Sugandhini

Question

n a Laboratory, you have the following chemicals available:

1.0 M NaOH, 1.00 M HCl, 1.00 M H3PO4, NaH2PO4 (s), Na2HPO4 (s), and Na3PO4 (s).

Describe TWO ways of making 1000 mL of a buffer of pH = 12 (Use only the above

chemicals, plus distilled water.)

[Given: H3PO4 - Ka1 = 6.9 x 10-3

; NaH2PO4 - Ka2 = 6.2 x 10-8

; Na2HPO4 - Ka3 = 4.8 x 10-13

]

Answer 1

Standard ratio for buffer preparation with pH = 12:

100 ml 0.1 M KH2PO4 + 53.8 mls of 0.1 M NaOH.

Recalculation gives:

3.549 g Na2HPO4

26.9 mls of 1.0 M NaOH

All adjusted to 1000 mL by distilled water