Aluminium is extracted from its ore by electrolysis - OCR Gateway - GCSE Chemistry: Combined Science - Question 17 - 2018 - Paper 1
Question 17
Aluminium is extracted from its ore by electrolysis.
This is an electrolysis cell.
Carbon anodes
Carbon lining of cell (cathode)
Aluminium oxide mixed with cryoli... show full transcript
Worked Solution & Example Answer:Aluminium is extracted from its ore by electrolysis - OCR Gateway - GCSE Chemistry: Combined Science - Question 17 - 2018 - Paper 1
Step 1
Explain why aluminium cannot be extracted by heating aluminium oxide with carbon.
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Answer
Aluminium cannot be extracted by heating aluminium oxide with carbon because aluminium is more reactive than carbon. In the reactivity series, aluminium's position is higher, meaning it cannot be displaced by carbon in a reaction to reduce aluminium oxide.
Step 2
Explain why cryolite is used.
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Answer
Cryolite is used in the electrolysis cell to lower the melting point of aluminium oxide. This increases the efficiency of the process by reducing energy consumption during electrolysis.
Step 3
Write a half equation for this reaction.
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Answer
The half equation for the reduction of aluminium ions at the cathode can be written as:
ightarrow Al$$
Step 4
Suggest why the anodes in the cell have to be replaced every few weeks.
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Answer
The anodes in the cell need to be replaced every few weeks because they react with oxygen to form carbon dioxide. This reaction gradually consumes the carbon anodes, leading to their degradation and the need for replacement.
Step 5
Write the overall balanced symbol equation for the electrolytic breakdown of aluminium oxide.
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Answer
The overall balanced symbol equation for the electrolytic breakdown of aluminium oxide, Al₂O₃, can be written as:
ightarrow 4Al + 3O_2$$
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