Ionic substances contain charged particles called ions. For example, lead bromide contains positively charged lead ions and negatively charged bromide ions.

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

Electricity is the flow of electrons or ions. For electrolysis to work, the compound must contain ions. Covalent compounds cannot act as electrolytes because they contain neutral atoms.

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

Two electrodes connected to a cell. The negative electrode attracts positive ions and the positive electrode attracts negative ions.

This is what happens during electrolysis:

  1. Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced.
  2. 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.


To be an electrolyte, a substance must be able to conduct electricity. To test for conductivity, include a sample of the substance in a circuit that contains a source of direct current (eg a cell or power pack) and a bulb or an ammeter. If a current flows through the substance when it is molten or dissolved, it is an electrolyte.