Calculate the pH of the solute in an aqueous solution of 0.0047 M codeine, if the pKa of itsconjugate acid is

Calculate the pH of the solute in an aqueous solution of 0.0047 M codeine, if the pKa of itsconjugate acid is 8.21.
What is the percentage protonation of the solute?

if pKa of itsconjugate acid is 8.21.
since pKa + pKb = 14
then its pKb = 5.79
& its Kb = 1.62 e-6


Base in wahter --> BH+ & OH-
Kb = [BH+] [OH-] / [B]

1.62 e-6 = [X] [X] / [0.0047]

X2 = 7.62 e-9

X = [OH-] = 8.73 e-5
pOH = 4.06

since pH + pOH = 14
when the pOH = 4.06,
the pH = 9.94