Choose the correct answer

Question

What is the PH of 0.15 M solution of the week acid ammonium bromide?

kb= 1.8*10^-5 for ammonia

a)11.22

b)8.96

c)2.78

d)5.04

Answer 1

Ammonium bromide = NH4Br

NH4⁺ + H2O ==> NH3 + H3O⁺

Ka = [NH3][H3O⁺]/[NH4⁺] and Ka = 1x10^-14/Kb = 1x10^-14/1.8x10^-5 = 5.6x10^-10

5.6x10-10 = (x)(x)/0.15

x2 = 8.4x10^-11

x = 9.2x10^-6 M = [H3O+]

pH = -log 9.2x10^-6

pH = 5.04 (answer d)