A solution is prepared by dissolving 0.23 mol of acetic acid and 0.27 mol of sodium acetate in water sufficient to yield 1.00 L of solution. What is the pH change (?pH) caused by the addition of 0.05 mol of HCl to this buffer solution? The pH does not change drastically because the HCl reacts with the ________ present in the buffer solution. The Ka of acetic acid is 1.4 × 10-4.