H3BO3 -> H+ + H2BO3-

Question

Why doesn't H3BO3 break down to something with H3O+ because it is a weak acid? I know many weak acids break down to something with H3O+ like HCN, C6H5COOH, HNO2, and HF.

Answer 1

It does. It is a Lewis acid but not a Bronsted-Lowry acid.
H3BO3 or B(OH)3.
B(OH)3 + HOH ==> H^+ + B(OH)4^
You can read more about it here.

http://en.wikipedia.org/wiki/Boric_acid-