How are borax and boric acid prepared ? Explain the action of heat on them.

Explanation

(1)Borax occurs naturally as tincol, associated with impurities in sediments of lakes . Borax is highly soluble in hot water but crystallises in cold water. So the tincol is dissolved in hot water and filtered to remove insoluble impurities. Then the filtrate is cooled to get the pure borax.
Borax on heating decomposes into sodium metaborate and boron trioxide which form a transparent glassy bead.
`Na_2B_4O_7. 10H_2O to ubrace(2NaBO_2 +B_2O_4)_"Transparent glassy bead" + 10H_2O`
(2) When borax is heated with conc. `H_2SO_4` , boric acid is formed.
`Na_2B_4O_7 + H_2SO_4 + 5H_2O to Na_2SO_4 + 4H_3BO_3`