Chemical Changes - Electrolysis - Revision Cards in GCSE Chemistry

Electrolysis

Electrolysis - The use of an electrical current to break down compounds containing ions into their constituent elements.
Electrolyte - The substance being broken down.
Electrodes - Solids that conduct electricity.
During electrolysis:
negatively charged ions move to the anode.
positively charged ions move to the cathode.
Electrolysis can be used to separate ionic compunds into elements.
Ionic substances can only conduct electricity when they are molten or dissolved in water.

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Reduction occurs when positively charged ions gain electrons at the negative electrode.
Oxidation occurs when negatively charged ions lose electrons at the positive electrode.
In a redox reaction both reduction and oxidation occur.
Reactions that take place at the electrodes can be represented by half-equations.

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Metals that are more reactive than carbon can be extracted from their ores using electrolysis.
Electrolysis requires lots of heat and electrical energy, making it an expensive process.

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When ionic compunds are dissolved in water to form aqueous solutions, it is slightly harder to predict the products of electrolysis.
The water molecules break down to form hydroxide ions, OH-, and hydrogen ions, H+.
At the negative electrode:
Hydrogen is produced if the metal is more reactive than hydrogen.
The metal is produced if the metal is less reactive than hydrogen.
At the positive electrode:
Oxygen is produced unless the solution contains halide ions.
If halide ions are present, then the halogen is produced.

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