Electrolysis and Metal Extraction

Key Concepts

• Electrolysis: A technique used to extract metals more reactive than carbon.
• Reactivity Series: Metals less reactive than carbon can be extracted by reduction with carbon. More reactive metals require electrolysis.

Example: Extraction of Aluminium

• Aluminium: Low density metal used in various products like drink cans and aircraft.
• Source: Extracted from aluminium oxide (Al₂O₃) through electrolysis.

Process Steps

1. Mix with Cryolite:

   • Aluminium oxide is mixed with cryolite to lower its melting point from ~2000°C, reducing energy costs.

2. Electrolysis Setup:

   • Electrodes: Made of graphite, a good conductor with a high melting point.
   • Electric Current: Applied to molten aluminium oxide.

3. Ions Movement:

   • Aluminium ions (Al³⁺): Move to the negative electrode (cathode), gain 3 electrons to become aluminium atoms.
   • Oxide ions (O²⁻): Move to the positive electrode (anode), lose 2 electrons to become oxygen atoms.

Higher Tier: Half Equations

• Cathode (Reduction Reaction):
  • Al³⁺ + 3e⁻ → Al
  • Aluminium ions gain electrons (reduction).
• Anode (Oxidation Reaction):
  • 2O²⁻ - 4e⁻ → O₂
  • Oxide ions lose electrons (oxidation).
  • Oxygen atoms pair up to form O₂ molecules.

Anode Considerations

• Replacement: The graphite anode must be replaced regularly.
  • Reason: Oxygen reacts with carbon to form CO₂, wearing down the electrode.

Cost of Electrolysis

• Energy Intensive:
  1. Melting Compound: Requires significant energy.
  2. Electric Current: High energy required to maintain the current.

Additional Resources

• Revision Workbook: For further practice on metal extraction using electrolysis.