Use the values of pKa1:2.12, pKa2:7.21 and pKa3:12.68 for H3PO4 to solve the following questions.

a) A 2 mL of 85% H3PO4 (density is 1.881 g/cm3) is diluted to 750 mL, calculate pH of this solution?

b) To prepare a buffer solution with pH 7.8, how many mL of Ba(OH)2 (strong dibase) containing 4110 ppm Ba2+ should be added to 250 mL of the diluted H3PO4 solution prepared in question (a)? (If you cannot find the concentration of the above diluted H3PO4 solution (a), take the concentration of the diluted H3PO4 solution as 0.048 M. In this case, the score of the question will be 80% of the actual score).

c) What will be the change in pH after 120 mL 0.025 M Ba(OH)2 and 200 mL 0.02 M Na2HPO4 have added to 100 mL of the diluted H3PO4 solution prepared in question (a)?