A buffer solution is made by adding 5.05 g of KOH (56.1 g/mol) to 500.0 mL of 0.400 M benzoic acid, HC7H5O2 (Ka = 6.6×10^-5)
Calculate the pH of the solution that results when 100.0 mL of 0.150 M HCl is added to the above buffer (total volume is 600.00 mL).