Calculate the pH at the equivalence point for the titration of 0.180 M methylamine (CH3NH2) with 0.180 M HCl. The Kb of methylamine is 5.0× 10^–4.

Answer 1

At the equivalence point we have the salt, CH3NH3Cl and it will hydrolyze to give you an acidic solution. (salt) at the equivalence point is 0.09M.
.........CH3NH3^+ + H2O == H3O^+ + CH3NH2
I.........0.09..............0........0
C...........-x..............x........x
E.......0.09-x..............x........x

Kb = (CH3NH2)(H3O^+)/((CH3NH3^+)
Substitute and solve for x = (H3O^+) and convert to pH.