The molar mass of anhydrous Na₂SO₄ = [2(23) + 32 + 4(16)]
= 142 g/mol
If the molar mass of hydrated Na₂SO₄ = 322 g/mol
Since hydrated salt = Anhydrous Salt + Water
Then the mass of hydration (Water)= 322 g/mol - 142 g/mol
= 180 g/mol
Since the molar mass of water itself is 18 g/mol
⇒ Moles of water = 180 g/mol ÷ 18g/mol
= 10
Thus n = 10; the formula of the hydrated salt is Na₂SO₄ · 10H₂O (Sodium Sulphate Decahydrate)
