What is pH of 0.1M solution of NH4Br, if the pKb of NH3 is 4.74?

Answer 1

.......NH4^+ + HOH ==> NH3 + H3O^+
I......0.1..............0.....0
C.......-x..............x.....x
E.....0.1-x.............x......x

Ka for NH4^+ = (Kw/Kb for NH3) = (x)(x)/(NH4^+)
Substitute and solve for x = (H3O^+) and convert to pH.

note: If pKb = 4.74 then Kb = 1.8E-5