1.615 g of anhydrous `ZnSO_(4)` was left in moist air. After a few days its weight was found to be 2.875 g. What is the molecular formula of hydrated salt ? (At. Mass: Zn=65.5, S=32, O=16, H=1)

Explanation

Molecular mass of anhydrous `ZnSO_(4)=65.5+32+64=161.5`
1.615 g of anhydrous `ZnSO_(4)` combine with `H_(2)O=2.875-1.615g=1.260g`
`therefore" 1.615 g of anhydrous "ZnSO_(4)" will combine with "H_(2)O=(1.260)/(1.615)xx161.5g`
`=126g=(126)/(18)"moles = 7 moles"`
Hence, formula of the hydrated salt = `ZnSO_(4).7H_(2)O.`