A) 7.0 ml of 85% H3PO4 (density: 1.67 g/ml) was diluted 750 ml with ultrapure water. Calculate pH of the solution.

B) To prepare 7.5 phosphate buffer solution, how much mL of 0.5 M NaOH should be added to 250 ml of diluted H3PO4 solution (a)? Ka1: 7.1x10^-2 Ka2: 6.2x10^-7 Ka3: 5.0x10^-13 for H3PO4.