Question

The crystalline salt $N{a}_{2}S{O}_4.x{H}_{2}O$ on heating loses 55.9% of its weight. The formula of the crystalline salt is

• A. $N{a}_{2}S{O}_4.5H_{2}O$
• B. $N{a}_{2}S{O}_4.7H_{2}O$
• C. $N{a}_{2}S{O}_4.2H_{2}O$
• D. $N{a}_{2}S{O}_4.6H_{2}O$
• E. $N{a}_{2}S{O}_4.10H_{2}O$

Answer 1

Answer: (E)

As $N{a}_{2}S{O}_4.x{H}_{2}O$ on heating loses water, i.e., 55.9% = 56% of its weight. $\therefore$ % of weight of $N{a}_{2}S{O}_4$ = 44% Molecular weight of $N{a}_{2}S{O}_4$ = 142 g $\therefore$ $\frac{w_{H_{2}O}}{w_{N{a}_{2}S{O}_4}}=\frac{56}{44}$ or $w_{H_{2}O}=\frac{56}{44}\times 142=180g$ Thus, the formula of crystalline salt is $N{a}_{2}S{O}_4.10H_{2}O$.