Q.How will you convert boric acid to boron nitride?

Boric acid, H₃BO₃ or B(OH)₃, is extracted from either borax or colemanite (e.g. Na₂B₄O₇ + H₂SO₄ + 5H₂O → 4H₃BO₃ + Na₂SO₄). It forms colourless, transparent crystals and is a very weak monobasic acid with an unusual mechanism: rather than donating a proton like an ordinary Brønsted acid, it accepts a hydroxyl ion from water, releasing a proton in the process -- B(OH)₃ + 2H₂O ⇌ H₃O⁺ + [B(OH)₄]⁻.

On progressively stronger heating it dehydrates in three stages -- to metaboric acid (373 K), then tetraboric acid (413 K), and finally to glassy boric anhydride (red heat). Fused with urea in an ammonia atmosphere it gives boron nitride. Heated with ethyl alcohol and conc. sulphuric acid it forms triethyl borate, whose vapour burns with a diagnostic green-edged flame -- the standard test used to identify a borate. It reacts with calcium fluoride (+ conc. H₂SO₄) to give boron trifluoride, and with soda ash to regenerate borax. …