A 0.250 M solution of a weak base has a pH of 9.45 . What is the base hydrolysis constant, 𝐾b , for the weak base? 𝐾b=

Answer 1

Let B represent the weak base.

B + H₂O ==> BH⁺ OH^-

Kb = [BH⁺][OH^-] / [B]

From the pH, we can find the pOH and then the [OH^- and BH⁺]:

pH + pOH = 14

pOH = 14 - pH = 14 - 9.45

pOH = 4.55

[OH-] = 2.82x10^-5 M = [BH⁺]

Kb = (2.82x10^-5)(2.82x10^-5) / 0.250

Kb = 3.18x10^-9