A mineral ore contains a mixture of compounds of lead and calcium, in approximately equal proportions - VCE - SSCE Chemistry - Question 7 - 2005 - Paper 1

At the positive electrode (anode), oxidation occurs. The half-reaction is:

$\text{Pb}^{2+} + 2e^- \rightarrow \text{Pb (s)}$

At the negative electrode (cathode), reduction occurs. The half-reaction is:

$\text{Ca}^{2+} + 2e^- \rightarrow \text{Ca (s)}$

If the concentration of Pb²⁺ decreases, the half-reaction at the anode may also involve oxidizing some of the Pb (s) back into Pb²⁺. The equation is:

$\text{Pb (s)} \rightarrow \text{Pb}^{2+} + 2e^-$

Using copper electrodes may lead to the oxidation of the copper instead of the expected oxidation of lead. The half-reaction at the anode would likely become:

$\text{Cu (s)} \rightarrow \text{Cu}^{2+} + 2e^-$