AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Metals can be extracted from molten compounds using electrolysis.
Full specification wording
Using electrolysis to extract metals: Metals can be extracted from molten compounds using electrolysis.
Electrolysis of a molten metal compound uses electrical energy to break the compound into its elements.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Electrolysis of a molten metal compound uses electrical energy to break the compound into its elements. 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.
What earns the marks
- 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.
Common mistakes and how to put them right
Thinking that the metal forms at the anode.
Put it right by stating that metal ions are positive and are attracted to the cathode.
Believing that solid compounds can be electrolysed.
Put it right by explaining that ions must be free to move, which requires the molten or aqueous state.
Confusing electrolysis with reduction by carbon.
Put it right by noting that electrolysis uses electricity, not carbon, to extract the metal.
Writing the metal ion as a neutral atom before electrolysis.
Put it right by showing the ion with its charge, such as Al³⁺.
Exam 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.
Try the lesson
The start of the Using electrolysis to extract metals: Metals can be extracted from molten compounds using electrolysis. lesson, made from checked teaching notes for this specification point.
Have a go first
Which process can be used to extract a metal from its molten compound?
Listen
Electrolysis of a molten metal compound uses electrical energy to break the compound into its elements. 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. A strong answer earns marks for these 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. A common slip: Thinking that the metal forms at the anode. Instead, stating that metal ions are positive and are attracted to the cathode. Exam tip: Always state that the compound is molten and explain why this is necessary.
See it
Put it in order
Put these steps in the order they happen.
- 1. Metal collected as a liquid or solid
- 2. Metal forms as a pure element at the cathode
- 3. Direct current passed through molten compound using electrodes
- 4. Metal ions gain electrons at the cathode
- 5. Metal compound is molten
- 6. Ions are free to move
- 7. Metal ions move to the negative electrode (cathode)
Key words
Say what each word means before you turn the card.
Electrolysis
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Molten compounds
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Redox at electrodes
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See every definition
- Electrolysis
- A process in which electrical energy is used to break a molten metal compound into its elements.
- Molten compounds
- Compounds that are molten so that their ions are free to move and conduct electricity.
- Redox at electrodes
- At the cathode, metal ions gain electrons to form the metal, making electrolysis a reduction process at the cathode.
Label the diagram
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1Box 1
2Box 2
3Box 3
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