[djmm187]

Why is it that a substance such as CH3NH2 containing no OH- increases the pH when dissolved in water?

[constant thinker]

Forum Rules

Google/check wikipedia before posting in the future.

A base doesn't have to have a hydroxyl group. It only needs to be able to accept H⁺ ions.

http://en.wikipedia.org/wiki/Br%C3%B8nsted-Lowry_acid-base_theory
http://en.wikipedia.org/wiki/Lewis_base

[davidbbk]

draw the Lewis structure for that molecule. You will notice there's a Lone Pair of electrons on the Nitrogen atom. Lone Pairs form an abnormally large electron cloud that can strongly interact with many atoms especially Hydrogen atoms. Remember that if H is bonded to N O or F and N O or F has 1 lone pair it is capable of Hydrogen bonding. Essentially, the N acts as a "Lewis Base". When a water molecule comes into contact with the Lone pair on this Lewis base, Hydrogen (already having a delta + charge do to the electronegativity of it's bonding in the water molecule) is easily lost  from the water molecule forming 0H-.

CH3NH2- + H20 <-----> CH3NH3 + OH-

thus the Hydroxide ion concentration increases thus you have a higher , more basic pH to the solution