A 0.75M solution of a weak base B, has a pH of 10.50

Question

a) write the Kb equation for B

b) calculate Kb-

Answer 1

B + H₂O ==> BH⁺ + OH^-

Kb = [BH⁺][OH^-]/[B]

pH = 10.50

pOH = 14 - 10.50 = 3.5

[OH^-] = 1x10^-3.5 = 3.16x10^-4 M

Kb = [(3.16x10^-4)(3.16x10^-4)/0.75

Kb = 1.33x10^-7