Borax

Author: Hans Lohninger

Ref.: Wikimedia Commons, user Aramgutang

The name borax (disodium tetraborate) generally describes a number of closely related compounds with different amounts of crystal water:

• borax decahydrate, Na₂B₄O₇10H₂O
• borax pentahydrate, Na₂B₄O₇5H₂O
• anhydrous borax, Na₂B₄O₇

When heated to temperatures beyond 350°C borax decahydrate loses its crystal water and forms anhydrous borax. Molten borax (m.p. 743°C) forms a glass-like bead which can readily dissolve metal oxides, developing a characteristic color which can be used in analytical chemistry for the detection of certain metals ("borax bead").

Borax is easily converted to boric acid by reaction with hydrochloric acid:

Na₂B₄O₇10H₂O + 2 HCl 4 H₃BO₃ + 2 NaCl + 5 H₂O

Borax occurs naturally in evaporite deposits of seasonal lakes (California, Turkey, Chile, Tibet, Romania). The biggest borax producer is California. Most of the borax world production is used in the glass and ceramics industry (for ceramic glazes, optical glasses, and laboratory glassware).