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A 250 mL solution of copper sulphate was electrolysed with a platinum anode and copper cathode. A steady current of 2 mA flowed for 16 minutes, after which the copper(II) concentration had dropped to half of its starting value. What was the original molar concentration of CuSO4?

1. 8.0 x 10⁻⁵ M
2. 2.0 x 10⁻⁵ M
3. 4.0 x 10⁻⁵ M
4. 1.0 x 10⁻⁴ M

Correct answer: 8.0 x 10⁻⁵ M

Solution

The charge deposits Cu metal, removing Cu2+ from solution. The amount removed equals 50% of the initial Cu2+. Work out moles of Cu deposited, set equal to half the initial moles, then divide by volume.

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