How many mL of 0.10 M HCl should be added to 100 mL of 0.10 M Tris base to make a buffer of pH 8.2? What is the molarity of Tris in this buffer? (pK of Tris (acid form) = 8.08)** Calculate the pH of a mixture containing 50 mL of 0.10 M NaH_2 PO_4 and 150 mL of 0.10 M Na_2 HPO_4. How many mL of 0.10 M H_3 PO_4 should be added to the above buffer to lower the pH by one unit? (pK of H_2 PO_4 = 6.82)