Calculate the percentage of pure aluminium in 10 kg. of aluminium oxide [Al₂O₃] of 90% purity. [Al = 27, O = 16]

90% of 10 kg = 9000 g

Molecular weight of aluminium oxide [Al₂O₃] = 2(27) + 3(16) = 54 + 48 = 102 g

102 g of aluminium oxide contains 54 g of aluminium

∴ 9000 g of aluminium oxide contains $\dfrac{54}{102}$ x 9000 = 4764 g = 4.764 kg of aluminium

∴ Percentage of pure Al in 10 kg. of aluminium oxide [Al₂O₃] = $\dfrac{4.764}{10}$ x 100 = 47.64%

Hence, percentage of pure aluminium in 10 kg. of aluminium oxide [Al₂O₃] of 90% purity is 47.64%