AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Using electrolysis to extract metals: Metals can be extracted from molten compounds using electrolysis. Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon. Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.
Electrolysis extracts a metal from its molten compound by passing direct current through the melt.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Electrolysis extracts a metal from its molten compound by passing direct current through the melt. The positive metal ions move to the cathode and form the metal, while negative non-metal ions move to the anode. (HT only: Metal ions gain electrons at the cathode, while non-metal ions release electrons at the anode). This route is chosen when carbon reduction is unsuitable: either the metal is more reactive than carbon, so carbon cannot displace it, or the metal reacts with carbon. For example, aluminium is extracted from molten aluminium oxide because aluminium is above carbon in the reactivity series. The process is energy-intensive: melting the compound requires heating to a high temperature, and maintaining the current requires a large electrical supply. Both demands make electrolysis expensive compared with reduction by carbon.
What earns the marks
- Electrolysis uses a direct electrical current passed through a molten compound, causing positive metal ions to move to the cathode to form the metal.
- Negative non-metal ions move to the anode, producing the non-metal element.
- Electrolysis is selected when the metal is too reactive to be extracted by reduction with carbon, because carbon cannot displace a more reactive metal from its compound.
- Electrolysis is also selected when the metal reacts with carbon, so carbon reduction would not yield the pure metal.
- Melting the compound requires a large energy input to overcome the lattice and produce mobile ions.
- Producing and maintaining the electrical current requires a large energy input, making electrolysis an expensive extraction method.
- (HT only) Explain that reduction occurs at the cathode (electron gain) and oxidation at the anode (electron loss).
Common mistakes and how to put them right
Thinking electrolysis can use a solid ionic compound.
Put it right by stating that the compound is melted to allow ions to move.
Assuming carbon reduction works for any metal.
Put it right by checking the reactivity series.
(HT only) Confusing oxidation and reduction.
Put it right by linking cathode to electron gain (reduction) and anode to electron loss (oxidation).
Exam tips
- When explaining why electrolysis is used, name the metal and compare its reactivity with carbon rather than giving a general statement.
- Link each energy cost to a specific stage: melting the compound and generating the current, so both parts of the statement are addressed.
- Avoid saying electricity 'breaks down' the compound without describing ion movement to the electrodes.
Try the lesson
The start of the Using electrolysis to extract metals: Metals can be extracted from molten compounds using electrolysis. Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon. Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current. lesson, made from checked teaching notes for this specification point.
Have a go first
Which process is used to extract a metal from its molten compound when the metal is too reactive to be extracted by reduction with carbon?
Listen
Electrolysis extracts a metal from its molten compound by passing direct current through the melt. The positive metal ions move to the cathode and form the metal, while negative non-metal ions move to the anode. HT only: Metal ions gain electrons at the cathode, while non-metal ions release electrons at the anode). This route is chosen when carbon reduction is unsuitable: either the metal is more reactive than carbon, so carbon cannot displace it, or the metal reacts with carbon. For example, aluminium is extracted from molten aluminium oxide because aluminium is above carbon in the reactivity series. The process is energy-intensive: melting the compound requires heating to a high temperature, and maintaining the current requires a large electrical supply. Both demands make electrolysis expensive compared with reduction by carbon. A strong answer earns marks for these points. Electrolysis uses a direct electrical current passed through a molten compound, causing positive metal ions to move to the cathode to form the metal. Negative non-metal ions move to the anode, producing the non-metal element. Electrolysis is selected when the metal is too reactive to be extracted by reduction with carbon, because carbon cannot displace a more reactive metal from its compound. Electrolysis is also selected when the metal reacts with carbon, so carbon reduction would not yield the pure metal. A common slip: Thinking electrolysis can use a solid ionic compound: the ions are fixed in the lattice and cannot move, so the compound must be molten or dissolved. Instead, stating that the compound is melted to allow ions to move. Exam tip: When explaining why electrolysis is used, name the metal and compare its reactivity with carbon rather than giving a general statement.
See it
Key words
Say what each word means before you turn the card.
Extraction of metals
Try answering aloud or in your head before turning the card.
Electrolysis of molten compounds
Try answering aloud or in your head before turning the card.
Reactivity series and carbon reduction
Try answering aloud or in your head before turning the card.
Energy costs in industrial processes
Try answering aloud or in your head before turning the card.
See every definition
- Extraction of metals
- Metals can be extracted from molten compounds using electrolysis, which is used if the metal is too reactive for reduction with carbon or reacts with carbon.
- Electrolysis of molten compounds
- A direct electrical current is passed through a molten compound, causing positive metal ions to move to the cathode and negative non-metal ions to the anode.
- Reactivity series and carbon reduction
- Electrolysis is used when the metal is too reactive to be extracted by reduction with carbon, because carbon cannot displace a more reactive metal from its compound.
- Energy costs in industrial processes
- Large amounts of energy are used to melt the compounds and to produce the electrical current, making electrolysis an expensive extraction method.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Using electrolysis to extract metals: Metals can be extracted from molten compounds using electrolysis. Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon. Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge