Is the boric acid a tribasic acid?

Answer 1

No, boric acid is NOT tribasic, although its formula suggests so with formula H3BO3.

It is a mono-basic, weak acid:

H3BO3 + H2O <<--> H3O+ + H2BO3-

with pKa = 9.24

and there is no second or third protolysis, noteven partially with strong base like OH-.

Boric acid is sometimes written as HBO2.(H2O) or more commonly as B(OH)3 [both equivalent to H3BO3].

This rewrites the above equation to this one:

B(OH)3 + 2H2O <<--> B(OH)4- + H3O+

with Ka = 5.8x10−10 ; pKa = 9.24