S5 - Extraction and uses of metals (aluminium)
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Name the process used to extract aluminium?
Electrolysis
Name the materials used for the electrodes
Graphite (carbon)
What are the polarity of the two electrodes?
Anode = + Cathode = -
What are the two compounds present in the liquid?
Aluminium oxide (alumina) and cryolite
What is the major cost of the attraction of aluminium?
Electricity
What is the element at the anode?
Oxygen
What is compound formed at the anode and explain how it forms.
Carbon dioxide - the oxygen produced at the anode combines with the carbon anode.
Why is molten aluminium oxide difficult to obtain?
The melting point is extremely high.
Give two reasons why cryolite is used in the electrolysis of aluminium oxide.
• to reduce the operating temperature of aluminium - its a solvent
Write the ionic half equation to show the formation of aluminium at the negative electrode (cathode)
Al3+ + 3e- —> Al
Write the ionic half equation to show the formation of oxygen at the positive electrode (anode)
2O- - 4e- —> O2
What type of process is the electrolysis of aluminium oxide?
Redox
What is being oxidised in the the ionic half-equations out of the formation of aluminium and oxygen?
The oxides have been oxidised to oxygen molecules (loss electrons)
What is being reduced in the the ionic half-equations out of the formation of aluminium and oxygen?
The aluminium ions have been reduced to aluminium atoms (gaining electrons)
Why do positive electrodes (anode) need replacing regularly?
They are warn out because they are reacting with the oxygen in the air to form carbon dioxide (C+O2 —> CO2)
Describe the structure of aluminium
A lattice of Al+++ ions hold together by delocalised electrons.
Why is aluminium a good conductor of electricity?
Delocalised electrons/ions can move freely around the structure with potential applied.
What is the main ore of aluminium that is purified to make alumina?
Bauxite Al2O3
Why doesn’t alumina powder conduct electricity?
The ions/electrons are stuck in the lattice unable to move freely.
Why aluminium cannot be extracted using coke in a blast furnace?
Aluminium is more reactive than carbon. Carbon cannot remove the oxygen from the aluminium.
What properties of aluminium are needed for the following: Aeroplane bodies Drink cans Overheated power cables Pans for cooking food
Aeroplane bodies - low density Drink cans - malleable Overheated power cables - conduct electricity Pans for cooking food - conducts heat well
What is meant by the term malleable?
Can be hammered into sheets
Explain why aluminium is malleable
Layers of aluminium atoms that can slide past each other freely.
What is meant by the term ductile?
Can be drawn out into wire