Overview
This lecture explains how aluminium is extracted from its ore using the electrolysis of aluminium oxide, including why this method is necessary and key steps in the process.
Extraction of Aluminium: Why Electrolysis?
- Aluminium is found in the ore bauxite, which contains aluminium oxide.
- An ore is a rock containing enough of a metal compound to be worth extracting.
- Aluminium is more reactive than carbon, so carbon cannot be used to extract it from its oxide.
- Electrolysis is needed to split aluminium oxide into aluminium and oxygen.
Electrolysis Process & Equipment
- Industrial electrolysis uses a large steel case called an electrolysis cell.
- The electrolyte is aluminium oxide, which must be molten or dissolved so ions can move.
- Aluminium oxide has a high melting point, so it is dissolved in molten cryolite to lower the melting point, saving energy and cost.
- DC power supply is used for electrolysis.
Structure and Roles of Electrodes
- The cathode (negative electrode) is made of graphite and lines the steel case.
- The anodes (positive electrodes) are also made from graphite and are immersed in the electrolyte.
Reactions at Electrodes
- Aluminium ions (Al³⁺) are attracted to the cathode, gain electrons, and become molten aluminium, collected at the cell's bottom.
- Oxide ions (O²⁻) move to the anode, lose electrons, and become oxygen gas (O₂).
- Oxygen produced at the anode reacts with the carbon anode to form carbon dioxide, causing the anode to wear away and require replacement.
Equations and Products
- Word equation: aluminium oxide → aluminium + oxygen
- Symbol equation must be balanced (not explicitly provided in transcript).
- Products of electrolysis: aluminium (at cathode) and oxygen gas (at anode).
Key Terms & Definitions
- Bauxite — the ore containing aluminium oxide.
- Electrolysis — the process of splitting a compound using electricity.
- Ore — a rock with enough metal compound to extract profitably.
- Cryolite — compound used to lower the melting point of aluminium oxide.
- Cathode — negative electrode where reduction occurs.
- Anode — positive electrode where oxidation occurs.
- Graphite — a form of carbon used for electrodes.
Action Items / Next Steps
- Practice answering questions about the extraction process.
- Balance the symbol equation for the electrolysis of aluminium oxide.
- Review why carbon cannot be used to extract aluminium.
- Study the reasons electrodes need regular replacement.