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