Borax

Preparation

It is prepared from naturally occuring calcium Borate. The mineral is boiled with concentrated solution of Na₂CO₃. The solution obtained in filteration is concentrated when crystals of Borax are deposited.

Ca₂B₆O₁₁ + 2Na₂CO₃ 3CaCO₃↓ + Na₂B₄O₇ + 2NaBO₂

CaCO₃ is filtered off. White needles of Borax separate out when hot solution is cooled.

Na₂B₄O₇ + NaBO₂ Na2B₄O₇↓ + NaBO2

Hotseparates

as white needle

On passing CO₂ gas to mother liquor containing NaBO₂ more Borax gets deposited.

4NaBO₂ + CO₂ Na₂B4O₇↓ + Na₂CO₃

Borax

Properties

(i) White needle having greater solubility in water. (Particularly in hot water)

(ii) Its aqueous solution is alkaline because of formation of strong base NaOH and weak acid H₃BO₄. Therefore it can be titrated against strong mineral acid useing methyl orange as indicator.

Na₂B4O₇ + 7H₂O 2NaOH + 4H₃BO₃

strong Boric acid (weak acid)

base

BORAX BEAD TEST (only given by coloured salts)

Na₂B4O₇.10H₂O Na₂B₄O₇ + 10H₂O

Na₂B₄O₇ NaBO₂ + B₂O₃

sodium Boron trioxide

meta Borate Borax Bead

(colourless, glassy)

This glassy bead reacts with a number of oxides giving characteristic coloured bead so this test is called Borax Bead test.

Cr₂O₃ + B₂O₃ Cr(BO₂)₃

 Chromium meta borate

(green bead)

NiO + B₂O₃ Ni(BO₂)₂

 (yellowish brown bead)

Nickel meta Borate

CuO + B₂O₃ Cu(BO₂)₂

 (Blue bead)

(Cu−Meta Borate)

If this blue bead is heated in a reduction flame it turns red due to formation of metallic copper.

CoO + B₂O₃ Co(BO₂)₂

(Blue)

Mn(BO₂)₄ is pink and Mn(BO₂)₂ is colourless in reduction flame.

INORGANIC GRAPHITE

Boron nitride, BN has a graphite−like layer structure of alternate B and N and hence it is known as inorganic graphite. It is prepared by the following reaction

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

INORGANIC BENZENE

Borazole, B₃N₃H₆ is an inorganic compound which possesses a cyclic ring structure similar to benzene with alternate single and double bonds. That is why it is called inorganic benzene.

3BCl₃ + 3NH₄Cl B3N3H₃Cl₃ B₃N₃H₆

Borazole