Impure copper can be purified using electrolysis. In this electrolysis • the anode is made of impure copper • the cathode is made from pure copper • the electrolyte is copper sulphate solution. The apparatus at the start of the experiment is shown in Figure 10. – 9021

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1. During electrolysis of copper(II) sulfate using copper electrodes, copper atoms at the anode lose electrons and become copper ions (Cu²⁺). This is called oxidation because electrons are lost. The equation is:
   Cu → Cu²⁺ + 2e⁻

   The copper ions go into the solution and move towards the cathode, which is negative. At the cathode, the copper ions gain electrons (reduction) and become copper atoms again:
   Cu²⁺ + 2e⁻ → Cu

   These copper atoms are deposited on the cathode, forming a pink or brown layer. This causes the cathode to get bigger or gain mass.

   Meanwhile, the anode gets smaller, because copper is leaving it and turning into ions. The blue colour of copper sulfate solution stays the same, because for every copper ion added from the anode, one is taken out at the cathode.

   Insoluble impurities from the anode fall to the bottom as a solid. This is how pure copper is collected during electrolysis.

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