Find the percentage of water of crystallisation in CuSO₄.5H₂O. (At. Mass Cu = 64, H = 1, O = 16, S = 32)

Relative molecular mass of CuSO₄.5H₂O

= 64 + 32 + (4×16) + [5(2+16)]

= 96 + 64 + 90 = 250

250 g of CuSO₄.5H₂O contains 90 g of water of crystallisation

∴ 100 g of CuSO₄.5H₂O contains

= $\dfrac{90}{250}$ x 100 = 36%