Question

A certain weak base has a Kb of 7.60 × 10-7. What concentration of this base will produce a pH of 10.27?

Answer 1

pH = 10.27

pOH = 14 - 10.27 = 3.73

[OH-] = 10^-3.73 = 1.86 x 10^-4 M = x

B + H2O --------------------> BH+ + OH-

C                                          0          0 -------------> initial

C-x                                      x            x ------------ equilibrium

Kb = [BH+][OH-] / [C-x]

7.60 × 10^-7 = x^2 / C-x

7.60 × 10^-7 = (1.86 x 10^-4)^2/ C- 1.86 x 10^-4

C = 0.046 M

concentration of base = 0.046 M