CH3NH3Br <====>
CH3NH3+ + Br-
CH3NH3+ + H2O
<===> CH3NH2 +
H3O+
ICE table:
                      Â
CH3NH3+Â Â Â Â Â Â Â Â Â Â Â Â Â
CH3NH2Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
H3O+
initial                Â
0.12Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0
change   -x +x   +x
equilibrium (0.12 - x) x
                         Â
x
pKb = -logkb = 3.35
pKa = 14 - 3.35 = 10.65
Ka = antilog(-pKa) = 2.23 x
10-11
Ka = x2/0.12Â Â Â Â (0.12
>> x)
2.23 x 10-11 x 0.12 = x2
x = 1.63 x 10-6 = [H+]
pH = -log[H+]
pH = 5.78
