Extracting aluminium with cryolite and carbon anodes, half equations at each electrode, masses of products, and the required practical on electrolysing solutions.
What you will learn
- Explain how aluminium is extracted and why it costs so much
- Choose the half equation at each electrode
- Calculate the mass of a product from electrolysis data
- Plan the electrolysis practical and test the products
Extracting aluminium
Aluminium is above carbon in the reactivity series, so its oxide cannot be reduced with carbon.
It is extracted by electrolysis of aluminium oxide.
- Aluminium oxide melts above 2000 °C, so it is dissolved in molten cryolite. This lowers the melting point and saves energy.
- At the cathode, Al³⁺ ions gain electrons and molten aluminium collects at the bottom.
- At the anode, O²⁻ ions lose electrons and oxygen forms. The anodes are carbon: the oxygen reacts with them to make carbon dioxide, so they burn away and are replaced regularly.
- The huge current and the heating make the process expensive.
- Al₂O₃ is 2 × 27 + 3 × 16 = 102
- fraction that is aluminium = 54 ÷ 102 = 52.9%
The rest of this lesson and its 14 practice questions are locked.
In this lesson
- Extracting aluminium
- Half equations (Higher)
- Required practical: electrolysing solutions
- Try it: Check the Mr values
14 practice questions, marked as you go; about 25 minutes in all.
Key terms
Cryolite, Copper electrodes
In this unit: Chemical changes: reactivity, acids and electrolysis
The reactivity series and metal extraction, oxidation and reduction, acids, salts and pH, titrations, and electrolysis of melts and solutions.