`13.4 g` of a sample of unstable hydrated salt `Na_(2)SO_(4).XH_(2)O` was found to contains `6.3 g` of `H_(2) O`. The number of molecular of water of crystalistion is

Options

A. 5
B. 7
C. 2
D. 10

Answer

B

Explanation

Weight of salt `= 13.4 g`
weight of `H_(2) O = 6.3 g`
Weight of anhydrous salt `= 13.4 - 6.3 = 7.1 g`
Moles of anhydrous salt `= (7.1)/(842) = 0.05`
Moles of `H_(2) O = (6.3)/(18) = 0.35 "mol"`
`0.05 "mol"` of anhydrous salt `implies 0.35 "mol of" H_(2)O`
1 mole of anhydrous salt `implies (0.35)/(0.05) = 7 "mol"`