Extracting Aluminium C6.3

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Why must aluminium be extracted via electrolysis?
Aluminium is quite high in the reactivity series so it is difficult to extract pure aluminium from its compounds.
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Why is aluminium oxide dissolved in molten cryolite?
Dissolving aluminium oxide in molten cryolite lowers the melting point of aluminium oxide which saves a lot of energy and money.
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What forms at the negative electrode?
Aluminium forms at the negative electrode.
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What forms at the positive electrode?
Oxygen forms at the positive electode.
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What is the positive carbon electrode called?
The positive carbon electrode is called the anode.
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What is the negative carbon electrode called?
The negative carbon electrode is called the cathode.
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What is the cathode made of?
The cathode is made of carbon.
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Explain why the extraction of aluminium in this way is reduction.
As we are removing the oxygen, it is a reduction reaction.
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Aluminium is extracted by the electrolysis of aluminium oxide. It is not possible to extract aluminium by heating aluminium oxide with carbon. Explain why.
The carbon wouldn't displace the aluminium as it is underneath aluminium in the reactivity series so it wouldn’t separate the aluminium and the oxygen. It is more reactive than carbon and it is too strongly bonded with the oxygen.
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Why must the positive electrode be continually replaced?
The oxygen reacts with the carbon of positive electrodes to produce carbon dioxide, so they gradually burn away and need to be replaced frequently.
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What advantages are there of recycling aluminium rather than extracting it from its ore?
It's easier to access as you don't have to re-extract it and it may be more sustainable. It would save money for electricity separating it and it would protect wildlife habitats.
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Why does the layer of aluminium oxide at aluminium's surface make it a very useful metal?
The layer of aluminium oxide slows down corrosion and makes it safer.
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Give two reasons why producing aluminium from this process can contribute towards global warming.
- The electrodes break down to produce CO₂
- They use fossil fuels to get the electricity.
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Why is aluminium such an expensive metal?
Aluminium is an expensive metal because it requires high amounts of energy to extract it.
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What happens with the ions during electrolysis?
During electrolysis, positive ions move towards the negative electrode and the aluminium ions are attracted to the cathode.
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Why is aluminium a useful metal?
It has a low density and a resistance to corrosion.
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Half equation at negative electrode
Al³⁺ (l) + 3e⁻ → Al (s) (reduction)
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Half equation at positive electrode
2O²⁻ (l) → O₂ (g)+ 4e⁻ (oxidation)
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Other cards in this set

Card 2

Front

Why is aluminium oxide dissolved in molten cryolite?

Back

Dissolving aluminium oxide in molten cryolite lowers the melting point of aluminium oxide which saves a lot of energy and money.

Card 3

Front

What forms at the negative electrode?

Back

Preview of the front of card 3

Card 4

Front

What forms at the positive electrode?

Back

Preview of the front of card 4

Card 5

Front

What is the positive carbon electrode called?

Back

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