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



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


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.


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