Determine the pH during the titration of 15.6 mL of 0.190 M perchloric acid by 5.90E-2 M barium hydroxide at the following points: (1) Before the addition of any barium hydroxide (2) After the addition of 12.6 mL of barium hydroxide (3) At the equivalence point (4) After adding 31.9 mL of barium hydroxide