Q. Show the Reactions of Boric Oxide?

Boric oxide, B₂0₃, is the principal oxide of boron. It is also known as boron trioxide, boron sesquioxide and boric anhydride. It is prepared by burning boron in oxygen or by heating boric acid to red heat:

2B + 30₂-------------------------> p B₂0₃

2H₃BO₃---------------------------> B₂0₃ + 3H₂0

Boric oxide is a white hygroscopic solid. It is acidic in nature and dissolves in water  to form boric acid:

B₂O₃ + 3H₂O---------------------------------> 2H₃BO3

When fused with metal salts, it forms, Meta borates known as borate glasses.  Meta borates of coloured cations have characteristic colours. This forms the basis of the borax-bead test in qualitative inorganic analysis, e.g.:

COO + B₂O₃------------------------------------->CO (BO₂)₂, deep blue

CuS0₄ + B₂0₃ ---------------------------------->CU (BO₂)_2, blue

Cr₂ (S0₄)₃ + B₂0₃-------------------------------> 2Cr (BO₂)₃, green

The bond energy of the B-0 single bond is very high (523 kJ mol^-1). Therefore, unlike carbon and nitrogen, boron does not form stable BO double bonds to oxygen.  Instead of forming small volatile covalent molecule, B₂0₃ (g) and small anion, B0³-₃3 it forms polymers having -B-0-B-0-B-0- chains. Thus, boric oxide is a polymeric solid.