Explain the physical and chemical properties of borax.

(N/A) Borax is the most important compound of boron.
Formula: The actual structure contains the tetranuclear units $[B_{4}O_{5}(OH)_{4}]^{2-}$,so the correct formula is $Na_{2}[B_{4}O_{5}(OH)_{4}] \cdot 8 H_{2}O$.
Physical Properties: It is a white crystalline solid. It dissolves in water to give an alkaline solution due to hydrolysis:
$Na_{2}B_{4}O_{7} + 7 H_{2}O \rightarrow 2 NaOH + 4 H_{3}BO_{3}$ (Orthoboric acid).
Chemical Properties (Borax Bead Test): On heating,borax loses water molecules and swells. On further heating,it turns into a transparent liquid that solidifies into a glass-like material called a borax bead:
$Na_{2}B_{4}O_{7} \cdot 10 H_{2}O$ $\xrightarrow{\Delta} Na_{2}B_{4}O_{7}$ $\xrightarrow{\Delta} 2 NaBO_{2} + B_{2}O_{3}$ (Sodium metaborate and Boric anhydride).
The metaborates of transition metals have characteristic colors,allowing for identification in the laboratory. For example,heating borax with $CoO$ on a platinum wire loop forms a blue $Co(BO_{2})_{2}$ bead.