Borax

Borax [Na₂B₄O₇.10H₂O]:

Preparation:

Borax is a sodium salt of tetraboric acid. It is obtained from colemanite ore by boiling its solution with sodium carbonate.

Borax is normally formulated as Na₂B₄O₇.10H₂O. But it contains, tetranuclear units [B₄O₅. (OH)₄]2-. This form is known as prismatic form. Borax also exists two other forms namely, jeweller or octahderal borax (Na₂B₄O₇.5H₂O) and borax glass (Na₂B₄O₇).

Properties

Borax is basic in nature and its solution in hot-water is alkaline as it dissociates into boric acid and sodium hydroxide.

Na₂B₄O₇ + 7H₂O → 4H₃BO₃ + 2NaOH

On heating it forms a transparent borax beads.

Borax reacts with acids to form sparingly soluble boric acid.

Na₂B₄O₇ + 2HCl + 7H₂O → 4H₃BO₃ + 2NaCl

Na₂B₄O₇ + H₂SO₄ + 5H₂O  → 4H₃BO₃ + 2Na₂SO₄

When treated with ammonium chloride it forms boron nitride.

Na₂B₄O₇ + 2NH₄Cl  → 2NaCl + 2BN + B₂O₃ + 4H₂O

Uses of Borax:

·           Borax is used for the identification of coloured metal ions

·           In the manufacture optical and borosilicate glass, enamels and glazes for pottery

·           It is also used as a flux in metallurgy and also acts as a preservative