The heating of 7.820 g of hydrated magnesium sulfate (MgSO4 • xH2O) crystals results in a mass of 3.547 g of anhydrous magnesium sulfate. Determine the formula of this hydrate. Name this formula.

MgSO₄•8H₂O

Magnesium sulfate octahydrate

Given

7.820 g of Magnesium sulfate (MgSO₄ • xH₂O)

3.547 g of anhydrous magnesium sulfate

Required

The formula

Solution

Mass of H₂O :

= 7.820 g - 3.547 g

= 4.273 g

MW MgSO₄=120 g/mol

MW H₂O = 18 g/mol

Mol ratio MgSO₄ : H₂O

= 3.547/120 g/mol : 4.273/18

= 0.0295 : 0.2374

= 1 : 8

The formula :

MgSO₄•8H₂O

Magnesium sulfate octahydrate