Electrolysis — Chemistry, 11–13 years
Electrolysis uses electricity to split a compound into simpler substances, showing that electrical energy can drive a chemical change.
Electricity pulls a compound apart
In electrolysis, an electric current passes through a suitable liquid or melted substance. The current makes particles move towards different electrodes, where new substances can form. It is not simply filtering or melting: the original compound is chemically changed into other substances.
Why use electricity?
Some compounds are held together so strongly that heating or filtering cannot separate them. Chemists needed a way to make useful elements from compounds such as molten salts or water. Electrolysis solves this by supplying energy and directing charged particles, although it requires electricity and suitable equipment.
Splitting water
In a safe apparatus, water is connected to a battery and two electrodes. Bubbles appear at both electrodes: hydrogen forms at one and oxygen at the other. Collecting the gases gives about 2 volumes of hydrogen for every 1 volume of oxygen. This matches the formula H₂O and the equation 2H₂O → 2H₂ + O₂.
The liquid disappears
It is tempting to say that the water has simply vanished when bubbles leave the apparatus. That makes sense if you see the liquid level fall and cannot see gases. In fact, water particles have been rearranged into hydrogen and oxygen, which occupy space and have different properties; they have not become nothing.
Making metals and hydrogen
Electrolysis is used to extract aluminium from its ore and to coat objects with a thin metal layer. It can also make hydrogen from water for research and some energy systems. These uses are real, but they need considerable electrical energy, so the source of that electricity affects how helpful the process is.
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