Question

$13.4\, g$ of a sample of unstable hydrated salt: $Na_2SO_4 \cdot nH_2O$ was found to contain $6.3\, g$ of water. Determine the number of water of crystallisation.

• A. $6$
• B. $5$
• C. $7$
• D. $8$

Answer 1

Answer: (C)

$\frac{\text{wt. of water}}{\text{wt. of sample}} = \frac{\text{wt. of water in the compound}}{\text{mol. wt. of the compound}}$
$\frac{6.3}{13.4} = \frac{x \times 18}{142 + 18\,x} x = 7$