Ortho boric acid & Borax

Ortho boric acid & Borax

source : web elements.com

Ortho boric acid ( H₃BO₃)

Method of preparation:

1) From Boron nitride:

When Boron nitride ( BN ) is hydrolysed by stream then ortho boric acid is obtained:

BN + 3H₂O ———>H₃BO₃ + NH₃

2) From borax:

Na₂B₄O₇ + H₂SO₄ ——–> H₂B₄O₇ + Na₂SO₄

H₂B₄O₇ + 5H₂O ———> 4H₃BO₃

 

Properties:

i) It is a weak mono-basic acid.

ii) It is sparingly soluble in water at room temperature.

iii)Effect of heat:

On heating it decomposes to give boric anhydride.

4)Reaction with ethyl alcohol:

When boric acid  reacts with ethyl alcohol, ethyl borate is formed which burns with green flame.

3C₂H₅OH +H₃BO₃ ———-> (C₂H₅)₃BO₃ + 3H₂O

5) sp² hybridization is present in BORON of H₃BO₃.

Uses of Ortho boric acid:

i) As antiseptic in face cream, powder and other cosmetic items.

ii) In making medicine for eyes.

 

Borax (Sodium tetra borate) Na₂B₄O₇ . 10H₂O

Common name : Suhaga

Method of preparation:

By the reaction of colemanite and Na₂CO₃ solution:

Ca₂B₆O₁₁ + Na₂CO₃ ———> Na₂B₄O₇ + CaCO₃ + NaBO₂

Properties:

i) It is colorless, crystalline solid, soluble in water.

ii) Hydrolysis:   Its  Aqueous solution is alkaline due to hydrolysis. On hydrolysis strong base  NaOH is obtained.

Na₂B₄O₇ +7 H₂0 ———>4 H₃BO₃ +2 NaOH

iii) Effect of heat:

Na₂B₄O₇ . 10H₂O ——–> Na₂B₄O₇ + 10H₂O

Na₂B₄O₇ ———-> 2NaBO₂              +        B₂O₃

(sodium meta borate)  (boric anhydride)

A transparent bead of  sodium meta borate & boric anhydride  is formed.

Uses:

1 ) It is used in making glass, soaps and candles.

2 ) In Borax bead test

Borax is heated on the loop of platinum wire  then a transparent bead of B₂O₃  and NaBO₂  is formed. This bead is called borax bead . This test is used to identify colored basic radicals present in the mixture like  Cu⁺⁺, Fe⁺⁺, Fe³⁺

Na₂B₄O₇ . 10 H₂O ———-> Na₂B₄O₇ + 10H₂O

Na₂B₄O₇ ———> 2NaBO₂ + B₂O₃

CuSO₄ + B₂O₃ ———> Cu(BO₂)₂ + SO₃

---