Chemical Changes: Electrolysis

• Electrolysis is the breaking down of a substance using electricity. The substance must be an ionic compound in a molten or dissolved state so that its ions are free to move.

• An electric current is passed through the substance using a battery or power supply wired to two electrodes.

• The negatively charged electrode, or cathode, attracts positive ions, and the positively charged electrode, or anode, attracts negative ions.

• This process separates the ionic compound into its elements.

• Reduction occurs at the cathode during electrolysis. Reduction is the gain of electrons by a species in a chemical reaction.

• Oxidation occurs at the anode during electrolysis. Oxidation is the loss of electrons by a species in a chemical reaction.

• An example of electrolysis is the decomposition of sodium chloride into sodium and chlorine. This happens by melting the sodium chloride, then applying electricity to it.

• When electrolysis is used to extract a metal from a metal ore, it is called electroplating. For example, copper can be extracted from copper sulphate solution through electrolysis.

• Electrolysis has many practical applications, including electroplating, purifying metals, and manufacturing chemicals.

• When carrying out electrolysis of aqueous solutions, water often competes with the solute for the electrons at the electrodes. The rules of electrolysis (“hydrogen is discharged if the metal is more reactive than hydrogen”; “the halogen is discharged if it is present”) will help predict the products.

• One practical you should be comfortable with is the electrolysis of copper sulphate solution with inert electrodes, observing the copper ions being reduced to copper atoms at the cathode.

• Always take precautions when electrolysis is performed in a laboratory setting, due to the production of potentially dangerous gases and the risk of electric shock.