Q.Explain what happens when boric acid is heated.

Borax, $Na_2[B_4O_5(OH)_4] \cdot 8H_2O$ (commonly written $Na_2B_4O_7 \cdot 10H_2O$), is boron's most important compound: it dissolves in water to give an alkaline solution and liberates orthoboric acid on hydrolysis ($Na_2B_4O_7 + 7H_2O \rightarrow 2NaOH + 4H_3BO_3$). On strong heating it loses water, swells, then melts to a glassy borax bead ($Na_2B_4O_7 \xrightarrow{\Delta} 2NaBO_2 + B_2O_3$), and this bead forms distinctively coloured metaborates with transition-metal oxides — the basis of the qualitative borax-bead test (e.g. cobalt oxide gives a blue bead). Orthoboric acid, $H_3BO_3$, is a white, soapy-feeling solid, prepared by acidifying borax with HCl. It has a layered, hydrogen-bonded structure of planar $BO_3$ triangles (Fig. 11.1) and is a weak, monobasic acid — crucially, it is NOT a …