4.4.3.3 using electrolysis to extract metals

What is alumnium used for

Low density

make drink cans, aircraft

Aluminium ion

Al³⁺

Oxide ion

O²⁻

Why is aluminium oxide mixed with cryolite first

Aluminium has a very high mo

This lowers it’s mp

Reduces the amount of money needed for electrolysis

This reduces the amount of energy needed and saves money

Why is the electrodes graphite

Have high mp

Good conductor of electricity

Why are ions free to move

It’s molten aluminium oxide

What happened at the cathode

Al³⁺ ions are attracted to the cathode

Each ion gains 3 electrons and forms an aluminium atom

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Half equation of alumnium

Al³⁺ + 3e⁻ —> Al (reduction)

What happens at the anode

O²⁻ Ions are attracted to the positive terminal

Each oxide loses 2 electrons to form an oxygen atom

Half equation for oxygen

2O²⁻ —> O + 4e⁻

2O²⁻ - 4e⁻ —> O

Why must the anode be replaced regularly

The oxygen molecules produced at the anode react with graphite (carbon) form carbon dioxide gas

C + O₂ - > CO₂

Why is producing metals by electrolysis expensive

Melting the compounds requires a lot of energy

A lot of energy is required to produce the electric current

Overall electrolysis equation of alumnium oxide

2Al₂O₃ (l)—> 4Al(l) + 3O₂ (g)