Boric oxide dissolves in water to form boric acid. In the process, it makes four strong covalent bonds to oxygen atoms to produce borate ions, as described previously:



Because hydrogen ions are produced, is an acidic oxide. Boric acid might better be written , to emphasize the proton that dissociates in water (center left).



Unfortunately, the usual practice is to leave out one water molecule and write boric acid as , creating the erroneous impression that it is a hydroxide compound and a base.

Boric acid is a very weak acid (see right). In aqueous solution, most of the substance is found as undissociated boric acid molecules and very little as borate ions, so the hydrogen ion contribution by boric acid is small. Dilute boric acid solution is mild enough to be used in eyewashes. (Don't try making your own. The results could be dangerous.)