A solution is prepared by dissolving 0.23 mol of lactic acid and 0.27 mol of sodium lactate in water sufficient to yield 1.00 L of solution. The addition of 0.05 mol of HCl to this buffer solution causes the pH to drop slightly. The pH does not decrease drastically because the HCl reacts with the present in the buffer solution. The Ka of lactic acid is 1.36 × 10-3.

A lactate ion
B H2O
C lactic acid
D H3O+
E This is a buffer solution: the pH does not change upon addition of acid or base.