Kb of the base?

Question

A weak base B forms the salt BHCl, composed of the ions BH+ and Cl-. A 0.164 M solution of the salt has a pH of 4.43. What is the value of Kb for the base B? Enter your answer in the form xE-y. Do not use units.

Answer 1

The equation is
B+H2O<==>BH+ +OH-
Kb=[BH+]*[OH-]/[B] (becasue [H2O]=1)
there is always
-Lg([H+]*[OH-])=14
PH=4.43
so [OH-]=1E-9.57
and here [BH+]=[OH-]
so Kb=[OH-]*[OH-]/(0.164-[OH-])=4.42E-19
x=4.42, y=19