The Extraction of Aluminium Flashcards
The three stage process of extraction of metals by electrolysis:
- Mining the ore
- Purification of the ore
- Electrolysis of the ore
The extraction of metal by electrolysis is _______.
Expensive
What is the major ore of aluminium?
Bauxite
What is the temperature to melt bauxite?
+2030 °C
What is the catalyst of this process?
Cryolite, lower melting point to 900 - 1000 °C
Only the ____ of aluminium gets rust.
Top
Aluminium is a _____, _____ and _____ so it is used for cables but it’s ______ so only used for big important things.
- Good conductor
- Light
- Strong
- Expensive
Why is aluminium expensive?
- Large amounts of energy are used in the extraction process
- Costly to replace anodes
What is bauxite purified to produce?
Aluminium oxide (Al₂O₃)
What can aluminium be extracted from?
Aluminium oxide (Al₂O₃)
What method of extraction is used?
Electrolysis
What is the name of the process?
Halt-Héroult Process
What state must the aluminium oxide be in for electrolysis to work?
Molten
Why must electrolysis be molten?
So that there are free electrons allowing an electrical current to pass through
Why is it expensive to melt aluminium oxide?
It has a very high melting point, (+2030 °C).
What do we do instead of melting aluminium oxide?
Dissolve it in molten cryolite
Why do we use molten cryolite instead of aluminium oxide?
It reduces some of the energy costs involved in extraction, lower melting point
What are both the anode and cathode made from in aluminium extraction electrolysis?
Graphite
Where does aluminium metal form?
At the cathode and sinks to the bottom of the tank, where it is tapped off
What forms at the anode?
Oxygen
What else happens at the anode?
The oxygen reacts with the carbon of the anode and forms carbon dioxide
Why do the anodes have to be frequently replaced?
The formation of carbon dioxide means that they gradually burn away
Oxidation occurs at the _____.
Anode
Reduction occurs at the _____.
Cathode
What does the Halt-Héroult Process involve?
- Dissolving aluminium oxide (alumina) in molten cryolite
* Electrolysing the molten salt bath
Half equation at anode.
2O⁻² → O₂ + 4e⁻
Half equation at cathode.
Al³⁺ + 3e- → Al
It is much _____ to _____ the metal.
- Cheaper
* Recycle
