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

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.

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

The equations for the reaction: Positive aluminium ions are attracted to the negative cathode, where they gain electrons and form aluminium metal. Al3+ +3e Al 2O2- -4e O2 Negative oxide ions are attracted to the positive anode, where they lose electrons and form oxygen gas.

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

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

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).