chemistry
posted by Nancy .
A 4.50e2 M solution of unknown monoprotic weak base has a pH of 10.200 what is the value of kb for the base

BOH ==> B^+ + OH^
Kb = (B^+)(OH^)/(BOH)
pH = 10.2; therefore, pOH = 3.8
pOH = log(OH^). Solve for OH^ and substitute into Kb expression. For (BOH) substitute 0.045(OH^).
Post your work if you get stuck. 
For pOH=log(OH) I solved to get OH=1.58e4
then I did kb=(4.50e2)(1.58e4)/.0451.58e4 to get 1.59e4 but that's not the right answer