


Use electrolysis to find out what substances is water made of

Suitable For

Grade 8



Time Required

 <2 Days



What’s it about?

All chemical substances or elements can be described in a shorthand method, for example H₂O for water, or CO₂ for carbon dioxide. Chemists often use this method of describing all the chemical substances, better known as a substance’s ‘chemical formula’.

A chart known as the ‘periodic table’ contains all the chemical elements according to their atomic number, weight, density and more. For instance Hydrogen’s formula is ‘H’ and oxygen’s formula is ‘O’ and water’s chemical formula is known as H₂O. This shows us that water is made up of 1 part oxygen and two parts hydrogen. Prove this is true in the following exciting science experiment – the electrolysis of water:

Topics covered

Chemical element, Periodic table, Oxygen, Electrolysis

What will I need?


Procedure (Method)


How does it work?


In electrolysis, the anode is the positive electrode and is where oxidation takes place. Oxidation involves the loss of electrons. The cathode is the negative electrode and is where reduction takes place. Reduction involves gain of electrons.

Think of water as hydrogen oxide (H2O). We can consider each hydrogen portion of water as H+. These would have to gain electrons (-) to become neutral hydrogen, therefore, this must happen at the negative electrode (the cathode). We can consider the oxygen part of water as O2- which has a negative charge hence would have to lose electrons to become neutral. Thus, oxygen gas should form at the positive electrode (the anode).

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