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80 g of copper sulphate pentahydrate, CuSO4.5H2O, is dissolved in deionised water to make 5 L of solution. The molar concentration of copper sulphate is x * 10⁻³ mol/L. Find x. (Atomic masses: Cu = 63.54, S = 32, O = 16, H = 1)

1. 64
2. 32
3. 100
4. 16

Correct answer: 64

Solution

Molar mass of CuSO4.5H2O is about 249.5 g/mol; 80 g gives 0.3206 mol in 5 L = 0.0641 M = 64 * 10⁻³ M.

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