Question

What mass (g) of Na2HPO4.2H,0 must be added to 570 mL of 0.140 M H,PO, to give a buffer of pH 7.257 (This problem requires values in your textbook's specific appendices, which you can access through the OWLv2 Mi not use the OWLv2 References Tables to answer this question as the values will not match.) Mass =

Answer 1

I Ans:- Given that pH = 7.25 ca) Concentration of = 0.140M - ₂PO4 - volume of solution = 570mL i Molar mass of Ng Apo 240=171.999 The stepwise dissociation constants for phosphoric and Ka, = 7.5x10²; Kq = 6.2x108; kom= 4.8x1013 pH = 7.25 = -log Ch? 0+] = 7.25 5. CH40+) - antilog (-1.25) => CM, 0+) = 5.62x158 M. Home Home Ho*: Kq = 6.28108 [Hot] CH ?). 6.2x108 CAPO] CHPO-2 } Chro] H2O + H2O 2 H pot Number of mmol Hp = 570 mL X 0.140 mmol/ml = 19.8 mmol. Number of mmol Klon in the buffes = 2x19.8 mmol = 159.6 mmol. 6.2x 108 1.1 5.62 5.62 *178 Number of mmol eeded for the butter = 1.1 X 159.6 rumol = 175.6 monol. .: 79.8 mmol of Na Hoog is needed to totally convest typog to H109 and an additional 115.6 mmol to provide the needed concentration of HPO 2 1.e. the concentration of Hooge = 79.8 mmol + 175. 6 mmol = 255.4 mmol, Mass of Natro 2 H2O = 255.4 monol x 0.17199 g/mol = 45.46 g.