Organic chem question regarding acid-base reaction?

Question

Okay, I have to write reactant of acid-base reaction.
I understand that I need to remove a proton from acid.
But how do i know which one is acid? I know acid is the
one donate proton , but how do i look at something like
NH2 + H20, and tell which one is acid

Answer 1

The H has to be ionized to be an acid. In the above example, only H2O can do that.

The full reaction is NH3 + H2O == NH4+ + OH-

NH3 receives the proton and is the B-L base. Water donates the proton and is the B-L acid