Strong base is dissolved in 655 mL of 0.200 M weak acid (Ka = 3.12 × 10-5) to make a buffer with a pH of 3.90. Assume that the volume remains constant when the base is added. a) Calculate the pKa value of the acid and determine the number of moles of acid initially present. b) When the reaction is complete, what is the concentration ratio of conjugate base to acid? c) How many moles of strong base were initially added?