A certain salt (X) gives the following tests: (i) Its aqueous solution is alkaline to litmus. (ii) On strong heating it swells to give a glassy material. (iii) When concentrated sulphuric acid is added to a hot concentrated solution of (X) white crystals of a weak acid separate out. Identify (X) and write down the chemical equations for reactions at steps (i). (ii) and (iii).

A certain salt (X) gives the following tests: (i) Its aqueous solution

1.	A certain salt (X) gives the following tests: (i) Its aqueous solution is alkaline to litmus. (ii) On strong heating it swells to give a glassy material. (iii) When concentrated sulphuric acid is added to a hot concentrated solution of (X) white crystals of a weak acid separate out. Identify (X) and write down the chemical equations for reactions at steps (i). (ii) and (iii).
Answer» Solution :The salt (X) swells on heating to give a glassy material, it seems to be borax `Na_(2)B_(4)O_(7)`, a well-known compound showing this property. This is also in accordance with the fact that ite-aqueous solution is alkaline to litmus and its reaction with conc. `H_(2)SO_(4)` to give crystals of a weak acid, `H_(3)BO_(3)` (boric acid). Thus, (X) is `Na_(2)B_(4)O_(7).10H_(2)O`. Chemical reactions: (i) `UNDERSET("Borax")(Na_(2)B_(4)O_(7))+7H_(2)Otounderset(ubrace"Strong base Weak acid"_("Alkaline"))(2NaOH+4H_(2)BO_(2))` (ii) `Na_(2)B_(4)O_(7)overset(heat)tounderset("Glassy BEAD")(2NaBO_(2)+B_(2)O_(2))` (iii) `Na_(2)B_(4)O_(7)+H_(2)SO_(4)+5H_(2)OtoNa_(2)SO_(4)+underset("Boric acid")(4H_(3)BO_(3))`