Question

Sol. Boric acid exists in polymeric form due to inter-molecular hydrogen bonding as shown in figure. The primary industrial use of boric acid is in the manufacture of monofilament fiberglass usually referred to as textile fiberglass. Boric acid is used in the production of the glass in LCD flat panel displays. It is a weak monobasic acid soluble in water and in aqueous solution the boron atom completes its octet by accepting OH− from water molecules.

B(OH)₃​ + 2H₂​O ⇌ [B(OH)₄​]⁻ + H₃​O⁺ Borax is also used as a buffer since its aqueous solution contain equal amounts of weak acid i.e boric acid and its salt.

[B₄​O₅​(OH)₄​] + 5H₂​O ⇌ 2[B(OH)₄​]⁻(salt) +2B(OH)₃​(weak acid)

Heating of boric acid :

H₃BO₃ $\overset{\quad 100ºC\quad}{\rightarrow}$ HBO₂ $\overset{\quad 140ºC\quad}{\rightarrow}$ H₂B₄O₇ $\overset{\quad\Delta red\text{ hot}\quad}{\rightarrow}$ B₂O₃

Metaboric acid tetraboric acid Glassy mass

H₃BO₃ + H₂O₂ → (H₂O) + (HO)₂ B–O–O–H $\overset{\quad NaOH\quad}{\rightarrow}$

Sodium peroxy borate used in washing powder as brightner