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

Explanation

`to` Preparation of Borax :
Boric acid on heating first forms tetraboric acid. This on reaction with sodium hydroxide to form borax.
`4H_3 BO_3 overset(435 K)to H_2 B_4 O_7 underset(-H_2 O)overset(2NaOH)to Na_2 B_4 O_7`
`to` Preparation of Boric acid : Borax is treated with conc.`H_2 SO_4` boric acid is formed.
`Na_2 B_4 O_7 + H_2 SO_4 + 5H_2 O to 4H_3 BO_3 + Na_2 SO_4`
Heating of Borax :
Borax on heating first loses the water molecules and forms sodium tetraborate. This on further heating forms a mixture of sodium meta borate and boric anhydride.
`Na_2 B_4 O_7 . 10 H_2 O overset(Delta)to Na_2 B_4 O_7 overset(Delta)to 2NaBO_2 + B_2 O_3`
Heating of Boric acid :
Boric.acid on heating forms boric anhydride. The reaction depends on the temperature used.
`2H_3 BO_3 overset("high temperature")to B_2 O_3 + 3H_2 O`
`2H_3 BO_3 overset(375 K)to HBO_2 overset("red hot")to B_2 O_3`
`4H_3 BO_3 overset(435 K)to H_2 B_4 O_7 overset("red hot")to B_2 O_3`