Question

A certain weak base has a Kb of 7.60 × 10-7 M. What concentration of this base will produce a pH of 10.14?

Answer 1

Kb = 7.60 × 10-7

pH = 10.14

[H+] = 10^-10.14 = 7.24 x 10^-11 M

[OH-] = 1.38 x 10^-4 M = x

B + H2O   -----------------> HB + OH-

C                                          0         0

C-x                                       x          x

Kb = x^2 / C - x

7.60 × 10^-7 = (1.38 x 10^-4)^2 / C - 1.38 x 10^-4

C = 0.0252 M

concentration of base = 0.0252 M