5.6 The Extraction Of Aluminium Flashcards
What does aluminium ore contain?
Aluminium oxide
What must be done to the aluminium before it can be electrolysed?
Purified and then melted
What does aluminium oxide melt at?
2000*C, needs lots of energy
What does aluminium oxide mixture with cryolite melt at?
850*C
What is made when aluminium oxide and cryolite are electrolysed at a lower temp?
Aluminium and oxygen
Why is aluminium oxide mixed with cryolite in the electrolysis cell?
To lower the melting temp
What is the overall reaction of aluminium in the electrolysis cell?
Aluminium oxide –> aluminium + oxygen
What happens to the cryolite in the electrolysis cell after the reaction has happened?
It remains in the cell and fresh aluminium oxide is added to repeat the process
What happens to the aluminium oxide at the negative electrode?
The aluminium ions are reduced to aluminium atoms as they gain electrons. The molten aluminium metal is collected from the bottom of the cell
What happens to the aluminium oxide at the positive electrode?
At the positive electrode oxide ions are oxidised to oxygen atoms by losing electrons and the oxygen atoms form oxygen molecules
What are the final products of the electrolysis cell?
Aluminium and carbon dioxide
What is the half equation at the negative electrode?
Al3+(l) + 3e- –> Al(l)
What is the half equation at the positive electrode?
2O(small 2+)(l) –> 2O2(g) + 4e-
What are the positive electrodes in the cell made of and why?
Carbon because at the high temp of the cell the oxygen reacts with the carbon to produce carbon dioxide
Why to the positive electrodes have to replaced regularly?
The carbon electrodes burn away gradually as it is made into carbon dioxide
