A certain salt $X$, gives the following results.

$(i)$ Its aqueous solution is alkaline to litmus.

$(ii)$ It swells up to a glassy material $Y$ on strong heating.

$(iii)$ When conc. $H_2SO_4$ is added to a hot solution of $X$, white crystal of an acid $Z$ separates out.

Write equations for all the above reactions and identify $X, Y$ and $ Z$.

$(i)$ The given salt is alkaline to litmus. Therefore, $X$ is a salt of a strong base and a weak acid. Also, when $\mathrm{X}$ is strongly heated, it swells to form substance $\mathrm{Y}$. Therefore, $\mathrm{X}$ must be borax.

$\mathrm{Na}_{2} \mathrm{~B}_{4} \mathrm{O}_{7} \cdot 10 \mathrm{H}_{2} \mathrm{O} \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} 2 \mathrm{NaOH}+\mathrm{H}_{2} \mathrm{~B}_{4} \mathrm{O}_{7}$

$(X)$

(Strong base) (Weak acid)

$(ii)$ When borax is heated, it loses water and swells to form sodium metaborate. When heating is continued, it solidifies to form a glassy material $Y$. Hence, $Y$ must be a mixture of sodium metaborate and boric anhydride.

$\mathrm{Na}_{2} \mathrm{~B}_{4} \mathrm{O}_{7} \cdot 10 \mathrm{H}_{2} \mathrm{O} \stackrel{\Delta}{\longrightarrow} \mathrm{Na}_{2} \mathrm{~B}_{4} \mathrm{O}_{7}+10 \mathrm{H}_{2} \mathrm{O}$

$\mathrm{Na}_{2} \mathrm{~B}_{4} \mathrm{O}_{7} \stackrel{\Delta}{\longrightarrow} \underbrace{2 \mathrm{NaBO}_{2}+\mathrm{B}_{2} \mathrm{O}_{3}}_{(\mathrm{Y})}$

$(iii)$ When concentrated acid is added to borax, white crystals of orthoboric acid $(Z)$ are formed. $\mathrm{Na}_{2} \mathrm{~B}_{4} \mathrm{O}_{7} \cdot 10 \mathrm{H}_{2} \mathrm{O}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow 4 \mathrm{H}_{3} \mathrm{BO}_{3}+5 \mathrm{H}_{2} \mathrm{O}+\mathrm{Na}_{2} \mathrm{SO}_{4}$