Question

1.00 g of a hydrated salt contains 0.2014 g of iron, 0.1153 g of sulfur, 0.2301 g of oxygen and 0.4532 g of water of crystallisation. Find the empirical formula. 

(At. wt. : Fe = 56; S = 32; O = 16)

Answer 1

Given :

Atomic mass of Fe = 56, 

S = 32, and 

O = 16

Mass of iron, sulphur, oxygen and water = 0.2014 g, 0.1153 g, 0.2301 g and 0.4532 respectively.

To find : 

The empirical formula of the compound

Calculation :

Since the mass of crystal is 1 g, the % iron, sulphur, oxygen and water = 20.14%, 11.53%, 23.01% and 4.32 % respectively.

Hence,

The ratio of number of moles of Fe:S:O water is \(\frac{0.360}{0.360}\) = 1, \(\frac{0.360}{0.360}\) = 1, \(\frac{1.438}{0.360}\) = 4, \(\frac{2.518}{0.360}\) = 7

Hence, 

Empirical formula is FeSO₄.7H₂O.

∴ Empirical formula of the compound = FeSO₄.7H₂O.