Aims of this Episode:

  • Describe the process of Electrolysis;
  • Identify the charge on the two different electrodes;
  • Explain the reactions that occur on each electrode;
  • Identify simple examples of Electrolysis.

What is needed for Electrolysis?

In order for Electrolysis to happen you need an ionic substance and two electrodes.

The ionic substance is known as the electrolyte. This is either molten (melted soil) or something dissolved as a solution. The electrolyte contains charged particles called ions – these can be positively charged (an atom with too few electrons) or negatively charged (an atom with too many electrons).

The electrodes are two pieces of metal connected to an electrical circuit. One will be positive (called the Anode) and one will be negative (called the Cathode). An easy way to remember this is PANIC: Positive Anode, Negative Is Cathode.

What happens during the reaction?

Once the electrical circuit is switched on the positive ions are attracted to the negative cathode and the negative ions are attracted to the positive anode.

When the positive ions arrive at the cathode, they gain some electrons – this is called Reduction.

When the negative ions arrive at the anode, they lose some electrons – the is called Oxidation.

A way to remember this is OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).

Reactivity Series

In the cases that the electrolyte is a solution (not molten), the reactivity series is an important consideration. If the metal in the solution is above Hydrogen in the reactivity series then instead of this metal being deposited at the cathode, Hydrogen gas is produced. If the metal is below Hydrogen then the metal is deposited as expected.

In addition to these basic principles of electrolysis, you need to be aware of the electrolysis of Aluminium and Brine.

Click here for the BBC Bitesize pages. Here is a video for Aluminium and here is one for Brine.

S@S 015: Electrolysis
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