A buffer consists of 3.0 M NH₃ (K_b = 1.8 X 10^-5) and 2.0 M NH₄Cl. What is the pH of this buffer after the addition of 1.5 moles of HNO₃ to 1.0 L of this buffer? (Assume the volume does not change on the addition of the HNO₃).