How does pKa relate to the final pH of a NH3/NH4Cl buffer system?

Question

How is this related to all buffers in general?

Answer 1

To calculate pH of a buffer solution you need to use Henderson Hassebalch equation:

pH = pKa + [A-}/[HA]

which in this case will be

pH = pKa + [NH3]/[NH4+]. The final pH will defend on pKa of this protonation and ratio of the two concentrations.