Chapter 5th:- Oxyacids of Boron, Phosphorus, and Sulphur
B.sc 1st year Book
Oxyacids of Boron
In oxyacids of boron, Borons several oxyacids which are commonly known as boric acids. Though all the acids may be regarded as aquated boric oxides. It involves a different number of water molecules e.g.
Orthoboric acid: H3BO3 or B2O3.3H2O
Metaboric acid: HBO2 or B2O3.H2O
Pyroboric acid: H6B4O9 or 2B2O3.3H2O
Tetraboric acid: H2B4O7 or 2B2O3.H2O
Phase studies of the system B2O3H2O. It shows that orthoboric acid and metaboric acid are stable oxyacids.
Orthoboric acid, H3BO3 or B(OH)3 :
- From borax or by treatment of borax with mineral acid (commercial method): Borax can be converted into boric acid by treatment with hydrochloric acid or sulphuric acid.
(i) By hydrolysis of boron compounds; BX3 where X = H, halogen, OR, NR2:
By the action of super-heated water on BN and B2S3: H3BO3 can be prepared by the action of super-heated water on boron nitride and boron sulfide as:
From colemanite: Most of the world’s supply of boric acid comes from the source. Crystals of boric acid are obtained when SO2 gas is passed into a suspension of the finely powdered mineral in hot water.