1. Electrolysis – background
Electrodes
Conducting liquid – electrolyte
Electrolysis is a chemical reaction. Current enters the electrolyte via two solid conductors called electrodes.

2. Electrolysis – background
Positive
electrode
Negative Electrode
ion+
ion-
ion-
ion+
ion+
ion-
Electrolyte
ion-
ion+
The anode is the positive electrode, and the cathode is the negative electrode.
The positive ions (cations) move towards the negative electrode, and the negative ions (anions) move towards the positive electrodes.

3. Electrolysis – extraction of reactive metals
Remove impurities by chemical method
Bauxite – a rock containing aluminium
Aluminium oxide powder (alumina), with a very high melting point
Electrolysis of aluminium oxide (alumina)
crust of solidified electrolyte
1. Aluminium oxide is dissolved in molten cryolite (about 950°C).
carbon anodes
aluminium oxide in molten cryolite
2. Oxygen gas is formed at the carbon anodes, and at that high temperature the anodes react with oxygen, burning away and having to be replaced from time to time.
Molten aluminium
tap hole
3. Aluminium in the form of a molten metal forms at the cathode.
4. The tap hole is used to collect the aluminium, the crust needs to be broken to add more aluminium oxide.
insulated cell casing
carbon lining to cell acting as the cathode

4. The equations for the reaction:
Positive aluminium ions are attracted to the negative cathode, where they gain electrons and form aluminium metal.
Al e Al
2O e O2
Negative oxide ions are attracted to the positive anode, where they lose electrons and form oxygen gas.

5. Locating aluminium works
A lot of electricity is required
for producing the metal via
electrolysis
The raw materials and the product
need to be transported easily
A good transport
network
in and out
Build aluminium works
near cheap sources
of electricity
Port
Railway links
Roads
Hydroelectric
Power Source
Nuclear Power Station

6. Properties of aluminium
light
strong
density of 2.7g/cm3
resistant to corrosion
layer of aluminium oxide (this prevents corrosion even though the metal is very reactive)
Using aluminium
Use
Reason
1. High voltage power cables for the
National Grid
Light, resistant to corrosion
2. Saucepans and kitchen foil
Good conductor of heat, non toxic
3. Window frames and greenhouses
Strong and light
4. Drinks cans
Strong and non toxic
5. Aeroplane and car bodies
Strong and resistant to corrosion

7. The consequences of metal extraction
Disadvantages
Advantages
When the ore runs out, the mine workings may be abandoned causing a deterioration of the landscape.
Extraction and processing of minerals creates employment.
Importing metals is very expensive for the country.
Sometimes less useful and toxic metals are found with the ones that are needed.
Important for the economy (Economic boom in the UK during Industrial Revolution).
Fluctuations in the cost of metals can affect the economy.
Processing minerals have a detrimental effect on the environment.
A lot of electricity is needed to produce aluminium.
Many minerals are sulphides – produce sulphur dioxide (the gas that causes acid rain).