Chapter 5th:- Oxyacids of Boron, Phosphorus, and Sulphur

B.sc 1st year Book
(Page 1)

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.

1. Orthoboric acid, H₃BO₃ or B(OH)₃ :

Preparation:

1. 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.

(more…)