What is electrolysis?

Electrolysis is the process by which ionic substances are decomposed into simpler substances when an electric current is passed through them.

For electrolysis to work, the ions must be free to move. Ions are free to move when an ionic substance is dissolved in water or when melted. For example, if electricity is passed through molten lead bromide, the lead bromide is broken down to form lead and bromine.

Here is what happens during electrolysis:

• Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced.
  
• Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised.
  

The substance that is broken down is called the electrolyte.

Electroplating

Electrolysis is used to electroplate objects. This is useful for coating a cheaper metal with a more expensive one, such as copper or silver.

• The negative electrode should be the object that is to be electroplated
• The positive electrode should be the metal that you want to coat the object with
• The electrolyte should be a solution of the coating metal, such as its metal nitrate or sulfate

Electroplating with silver

The object to be plated, such as a metal spoon, is connected to the negative terminal of the power supply. A piece of silver is connected to the positive terminal. The electrolyte is silver nitrate solution.

Electroplating with copper

The object to be plated, such as a metal pan, is connected to the negative terminal of the power supply. A piece of copper is connected to the positive terminal. The electrolyte is coppersulfate solution.

This arrangement can also be used to purify copper during copper manufacture. In this case, both electrodes are made from copper. The negative electrode gradually gets coated with pure copper as the positive electrode gradually disappears.

Aluminium extraction

Aluminium is the most abundant metal on Earth. But it is expensive, largely because of the amount of electricity used up in the extraction process.

Aluminium ore is called bauxite. The bauxite is purified to yield a white powder -aluminium oxide - from which aluminium can be extracted.

The extraction is done by electrolysis. But first the aluminium…