A buffer contains 0.015 mol of lactic acid (pKa = 3.86) and 0.090 mol of sodium lactate per liter. .. .. OH O Nat OH OH Lactic acid Sodium lactate Calculate the pH of the buffer. buffer pH: Calculate the change in pH after adding 4.5 mL of 0.50 M HCl to 1.0 L of the buffer. buffer pH change: units Calculate the change in pH after adding 4.5 mL of 0.50 M HCl to 1.0 L of pure water. water pH change: units