pH = 9.788
pH + pOH = 14
pOH = 14 - 9.788
pOH = 4.212
[OH-] = 10^-4.212 = 6.14 x 10^-5 M = x
Kb = 2.105 × 10^-5
B + H2O ---------------------> BH+Â Â + OH-
C
-x                                      Â
x           Â
x
Kb = x^2 / C - x
2.105 × 10^-5 = (6.14 x 10^-5 )^2 / C - 6.14 x 10^-5
C - 6.14 x 10^-5 = 1.77 x 10^-4
C = 2.38 x 10^-4 M
amine protonated = ( x / C ) x 100
                           Â
  = (6.14 x 10^-5 / 2.38 x 10^-4 ) x 100
                             Â
= 25.78 %
