Its acidic source is not the proton itself, because boron is an electron-deficient atom, which can add hydroxyl ions of water molecules and release protons. Taking advantage of this lack of electrons, polyhydroxy compounds (such as glycerol and glycerol) are added to form a stable complex to strengthen its acidity.

Reasons why boric acid is obviously acidic:

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B(OH)3+2H2O====[HO - B - OH]- + H3O+

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Is boric acid a monobasic acid or a polybasic acid?

Boric acid is a very weak acid, but some textbooks and manuals mention that boric acid is a ternary acid with a third-order ionization constant. In the paper 1930 by F.L.Hahn et al., the pKa 1 of boric acid is 9.24, pka2 is 12.74, and pka3 is 13.4. Later, N.Ingri and others made an in-depth study on this issue in the 1960s, and studied the equilibrium of boric acid by potential method. It is not confirmed that borate ions with average charge number less than-1 exist in the aqueous solution, that is, there are no high valence anions such as HBO3 2- or BO3 3- in the solution. Chinese scholars Song, Wang and others also proved that there should be no secondary and tertiary ionization through theoretical calculation. The experimental method failed to prove that boric acid has a second-order and third-order dissociation equilibrium, so boric acid can only be considered as a monobasic acid. In some textbooks and handbooks, it is not appropriate to use Ka 1 to express the dissociation constant of boric acid, because it leads to the incorrect concept that boric acid has multistage dissociation in aqueous solution, so it is suggested to use Ka instead.

After glycerol is added to boric acid, the acidity of boric acid will be enhanced.

The formed borate ester burns to produce a green flame, which can be used to identify boron-containing compounds.