What is the difference (in pH units) between the initial pH of a 0.20 M NH3 / 0.20 M NH4Cl buffer to the pH of the buffer after the addition of 10.0 mL of 0.10 M HCl to 65.0 mL of the buffer? (Ka of NH4+ at 25°C = 5.6 x 10?10) A. final pH is 0.07 pH units lower than original pH B. final pH is 0.16 pH units higher than original pH C. final pH is 0.07 pH units higher than original pH D. there is no measurable difference between final and initial pH - that is why it is called a buffer E. final pH is 0.16 pH units lower than original pH