Borax is prepared from

Options

A. boric acid
B. colemanite
C. tincal
D. all of these

Answer

D

Explanation

By neutralizing boric acid with sodium carbonate:
`4H_(3)BO_(3) + Na_(2)CO_(3) rarr Na_(2)B_(4)O_(7) + 6H_(2)O + CO_(2)`
The crystals of borax `(Na_(2)B_(4)O_(7) . 10H_(2)O)` separate out when the solution is cooled.
Finely divided mineral colemanite `(Ca_(2)B_(6)O_(11))` is boiled with sodium carbonate solution:
`Ca_(2)B_(6)O_(11) + 2Na_(2)CO_(3) overset(Delta)rarr Na_(2)B_(4)O_(7) + 2NaBO_(2) + CaCO_(3)`
Sodium metaborate `(NaBO_(2))` can also be converted into borax by treatment with carbon dioxide:
`4NaBO_(2) + CO_(2) rarr Na_(2)B_(4)O_(7) + Na_(2)CO_(3)`
Naturally occuring borax is called tincal. It is obtained from dried-up lakes in locatons that once had intense volcanic activity and contains about `50%` borax. It is boiled with water and filtered to remove insoluble impurities. The crystals of borax separate out when the filtrate is concentrated.