[Nescafe]

Hi,

I have been reading about this topic and generally seems like organic chemists tend to think of things in terms of their pKa instead of pKb. For intsance NH3 and NH4+, pKa for NH4+ is 9.3 (the pKb for its conjugate base, NH3, is 4.7).  The pKa for NH3 on the other hand is 33, what I want to know is the pKb for the conjugate base of NH3, so ^-NH2? Or is this not possible to determine? Why is it that when it comes to pKa and pKb discussions it seems that the following equation holds true only when you are looking at the conjugates.

pKa + pkb = 14 for only conjugates (NH4+ and its conjugate base, NH3)

Any help would be appreciated,

Nescafe.