NH3 is a weak base (Kb = 1.8 × 10–5) and so the salt NH4Cl acts as a weak acid. What is the pH of a solution that is 0.049 M in NH4Cl at 25 °C?

Answer 1

.........NH4^+ + H2O ==> H3O^+ + NH3
I......0.049..............0.......0
C........-x...............x.......x
E.....0.049-x.............x.......x

Ka for NH4^+ = (Kw/Kb for NH3) = (x)(x)/(0.049-x)
Solve for x = (H3O^+) and convert to pH.