Borax

Borax

Borax is the most important compound of boron. It is a white crystalline solid of formula Na₂B₄O₇.10H₂O. in fact it contains the tetranuclear units [B₄O₅(OH)₄]^2-  and correct formula; therefore, is Na₂[B₄O₅(OH)₄]. 8H₂O. borax dissolves in water to give an alkaline solution.

Na₂B₄O₇  +  7H₂O    →    2NaOH   +   4H₃BO₃

                                                           Orthoboric acid

On heating, borax first loses water molecules and swells up. On further heating it turns into a transparent liquid, which solidifies into glass like material known as borax bead.

Na₂B4O₇.10H₂O(Heat)    →    Na₂B₄O₇ (Heat)   →   2NaBO₂    +    B₂O₃

                                                               Sodium  metaborate    Boric Anhydride

                                                                                                      

The metaborates of many transition metals have characteristic colors and, therefore, borax bead test can be used to identify them in the laboratory. For example, when borax is heated in a Bunsen burner flame with CoO on a loop of platinum wire, a blue colored Co(BO₂)₂ bead is formed.