Borax (Na2B4O7.10H2O)

Borax is the sodium salt of boric acid. B orax occurs naturally as tincal (suhaga) in certain dried up lakes of india, Tibet, Srilanka and USA. It contains about 55% borax.

PREPERATION:-

From tincal:Tincal is boiled with water and the so;ution is then filtered to remove impurities of sand, clay etc. The filterate is concentrated till crystallization begins and then cooled. The crystals of borax are separated by filteration.

From colemanite (Ca2B6O11):

Ca2B6O11 + 2Na2CO3 -----Heat-----» Na2B4O7 + 2NaBO2 + 2CaCO3↓

4NaBO2 + CO2 -----------» Na2B4O7 + Na2CO3

The insoluble calcium carbonate is filtered off .The remaing solution containg of borax and sod.metaborate is then treated with CO2 to convert sod.metaborate to borax.The solution is now concentrated and cooled to crystallize borax

Boric acid is prepared by treatingborax withnitric acid.Nitric acidispreferred to hydrochloric acid because sodium nitrate is morereadily soluble than sodium chloride.Sulfuric acidis notemployed because it is not so readily washed out.