ELECTROLYSIS -- 5.4.3.3 Using electrolysis to extract metals Flashcards
(19 cards)
What is electrolysis used for?
Electrolysis is used to extract metals from molten compounds.
When is electrolysis needed for extraction?
When a metal is too reactive to be extracted with carbon.
Which metals are commonly extracted using electrolysis?
- Aluminium
- Sodium
- Magnesium
Why is electrolysis used instead of carbon reduction?
- Metals higher than carbon in the reactivity series cannot be extracted by carbon reduction.
- Some metals, like aluminium, react with carbon, making reduction ineffective.
- Electrolysis forces metal ions to gain electrons and turn into pure metal.
Why is electrolysis expensive?
- High energy cost – Large amounts of electricity are needed.
- Melting compounds – The metal oxide must be molten for electrolysis to work.
- Maintaining electrodes – Electrodes may react and need replacing.
What is the raw material for extracting aluminium by electrolysis?
Bauxite (contains aluminium oxide, Al₂O₃)
What is the electrolyte used in the electrolysis of aluminium oxide?
Molten aluminium oxide mixed with cryolite.
What type of electrodes are used in the electrolysis of aluminium oxide?
Carbon (graphite) electrodes.
What is the purpose of using cryolite in the electrolysis process?
- Lowers the melting point of aluminium oxide.
- Reduces energy costs and makes the process more efficient.
What occurs at the cathode during the electrolysis of aluminium oxide?
Al³⁺ ions gain electrons (reduction) → Aluminium metal forms.
What is the equation for the reaction at the cathode?
Al³⁺ + 3e⁻ → Al (Molten aluminium collects at the bottom)
What occurs at the anode during the electrolysis of aluminium oxide?
O²⁻ ions lose electrons (oxidation) → Oxygen gas forms.
What is the equation for the reaction at the anode?
2O²⁻ → O₂ + 4e⁻ (Oxygen bubbles off)
Why must the positive electrode (anode) be replaced regularly?
Oxygen reacts with carbon, forming carbon dioxide (CO₂), which wears away the electrode.
What is the reaction at the anode?
C + O₂ → CO₂ (Carbon burns away)
What happens to the carbon electrodes during electrolysis?
They may react with oxygen, forming CO₂ and need to be replaced.
Fill in the blank: Electrolysis is used to extract metals from _______.
[molten compounds]
True or False: Aluminium can be extracted using carbon reduction.
False
What are the key exam pointers related to electrolysis?
- When is electrolysis needed for extraction?
- Why is cryolite used?
- What happens at the cathode?
- What happens at the anode?
- Why must the anode be replaced?
