If the pH of a 0.46 M aqueous solution of a weak base is 9.2, estimate the Kb of the base:

Answer 1

pH + pOH = pKw = 14. Solve for pOH.
Then pOH = -log(OH^-). Solve for (OH^-).
Call the weak base BOH.

.......BOH ==> B^+ + OH^-
I......0.46....0......0
C......-x......x......x
E....0.46-x....x......x

You know x from above. Substitute x and 0.46-x into the Kb expression and solve for Kb. Piece of cake.