You are asked to prepare a pH of 4.00 buffer starting from1.50 L of 0.0200 M solution of benzoic acid and an excess of sodium benzoate. A. what is the pH of the benzoic acid solution prior to adding sodium benzoate? B. how many grams of sodium benzoate should be added to prepare the buffer? neglect the small volume change that occurs when the sodium benzoate is added.