Using electrolysis to extract metals — AQA GCSE Chemistry
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Using electrolysis to extract metals explained
Electrolysis of a molten metal compound uses electrical energy to break the compound into its elements.
Read the full explanation
The molten compound contains metal ions and non-metal ions that are free to move. When a direct current is passed through the molten compound, metal ions move to the negative electrode (cathode) and gain electrons to form the metal. For example, molten aluminium oxide yields aluminium at the cathode. The extracted metal can be collected as a liquid or solid. This method is used when the metal cannot be extracted by reduction with carbon. The process requires the compound to be molten so that ions can move and conduct electricity. Assessment may ask you to describe the method, name the product at the cathode, or explain why the compound must be molten.
Your focus
- Describe how electrolysis extracts a metal from its molten compound.
- Identify the cathode as the site of metal formation.
- Explain why the compound must be molten for electrolysis to occur.
Using electrolysis to extract metals exam tips
Marking Points
- State that the metal compound must be molten so that its ions are free to move.
- Describe the passage of direct current through the molten compound using electrodes.
- Identify the cathode as the negative electrode where metal ions gain electrons.
- Write the half-equation for the metal ion gaining electrons, for example Al³⁺ + 3e⁻ → Al.
- Explain that the metal is extracted as a pure element at the cathode.
- Recognise that electrolysis is a reduction process at the cathode because electrons are gained.
Examiner Tips
- 💡Always state that the compound is molten and explain why this is necessary.
- 💡Link the electrode to the type of ion attracted to it.
- 💡Use the term 'reduction' correctly for the cathode process.
Common Mistakes
- Thinking that the metal forms at the anode: correct this by stating that metal ions are positive and are attracted to the cathode.
- Believing that solid compounds can be electrolysed: correct this by explaining that ions must be free to move, which requires the molten or aqueous state.
- Confusing electrolysis with reduction by carbon: correct this by noting that electrolysis uses electricity, not carbon, to extract the metal.
- Writing the metal ion as a neutral atom before electrolysis: correct this by showing the ion with its charge, such as Al³⁺.