Purifying copper by electrolysis

Copper is purified by electrolysis. Electricity is passed through solutions containing copper compounds, such as copper(II) sulfate. The anode (positive electrode) is made from impure copper and the cathode (negative electrode) is made from pure copper.

Pure copper forms on the cathode. The slideshow shows how this works:

Beaker with pure and impure copper rods dipping into copper(II) sulfate solution.

Purifying copper by electrolysis

1. A beaker with pure and impure copper rods dipped into copper(II) sulfate solution

During electrolysis, the anode loses mass as copper dissolves, and the cathode gains mass as copper is deposited.

The slideshow shows what happens during the purification of copper by electrolysis:

Two vertical copper rods. Four Cu ions are attached to the rod on the right, and four Cu2+ ions are floating in the space between the rods.

The purification of copper by electrolysis

1. Four Cu ions are attached to the rod on the right, and four Cu²+ ions are floating in the space between the rods

A half-equation shows what happens at one of the electrodes during electrolysis. Electrons are shown as e-.

These are the half-equations:

anode: Cu → Cu2+ + 2e- (oxidation)

cathode: Cu2+ + 2e- → Cu (reduction)

Oxidation happens at the anode because electrons are lost. Reduction happens at the cathode because electrons are gained.

One way to remember this is by using the mnemonic OIL RIG:

Oxidation Is Loss of electrons, Reduction Is Gain of electrons.