A sample of hydrated copper sulphate is heated to drive off the water

1.	A sample of hydrated copper sulphate is heated to drive off the water of crystallization, cooled and reweighed 0.869 g of CuSO4 aH2O gave a residue of 0.556 g. Find the molecular formula of hydrated copper sulphate.
Answer» 0.869 g of CuSO₄ .aH₂O gave a residue of 0.556 g of Anhydrous CuSO₄ . ∴ Weight of a H₂O molecule = 0.869 – 0.556 = 0.313 g Molecular weight of H₂O = (1 x 2) + 16 = 2 + 16 = 18 No. of moles of water = Mass / (Molecular mass) CuSO₄.5H₂O – Molecular mass = 63.5 + 32 + 64 + 90 = 249.5 g 249.5 g of CuSO₄.5H₂O on heating gives 159.5 g of CuSO₄ . 0.869 g of CuSO₄.aH₂O on heating gives = 159.5/249.5 x 0.869 = 0.556 g of anhydrous CuSO₄. ∴ a = 5 The molecular formula of hydrated copper sulphate = CuSO₄.5H₂O

A sample of hydrated copper sulphate is heated to drive off the water of crystallization, cooled and reweighed 0.869 g of CuSO4 aH2O gave a residue of 0.556 g. Find the molecular formula of hydrated copper sulphate.

Answer»

0.869 g of CuSO₄ .aH₂O gave a residue of 0.556 g of Anhydrous CuSO₄ .

∴ Weight of a H₂O molecule = 0.869 – 0.556

= 0.313 g

Molecular weight of H₂O = (1 x 2) + 16

= 2 + 16

= 18

No. of moles of water = Mass / (Molecular mass)

CuSO₄.5H₂O – Molecular mass = 63.5 + 32 + 64 + 90 = 249.5 g

249.5 g of CuSO₄.5H₂O on heating gives 159.5 g of CuSO₄ .

0.869 g of CuSO₄.aH₂O on heating gives = 159.5/249.5 x 0.869 = 0.556 g of anhydrous CuSO₄. ∴ a = 5

The molecular formula of hydrated copper sulphate = CuSO₄.5H₂O