With the aid of a labelled diagram,explain how molten Aluminium Oxide (bauxite) is electrolysed.
Bauxite is the ore. Aluminum oxide (alumina) is the intermediate.
Here is a good diagram with labels. Better than I can draw.
http://www.elmhurst.edu/~chm/onlcourse/chm110/outlines/aluminum.html
To explain how molten aluminum oxide (bauxite) is electrolyzed, let's first understand the process of electrolysis:
Electrolysis is a process that involves the decomposition of a compound using an electric current. It occurs when an electric current is passed through an electrolyte (a substance that conducts electricity when dissolved or melted). In this case, molten aluminum oxide acts as the electrolyte.
Now, let's break down the process of electrolyzing molten aluminum oxide with the help of a labeled diagram:
1. Setup:
- A container, known as the electrolysis cell, is made of a refractory material, as it must withstand high temperatures. This container is labeled "Electrolysis Cell."
- The cell is divided into two compartments by a ceramic or graphite barrier called the "diaphragm." The diaphragm allows the passage of ions but prevents mixing of the products.
- Two graphite electrodes, labeled "Cathode" and "Anode," are placed into each compartment of the cell. These electrodes are connected to the positive and negative terminals of a direct current (DC) power supply.
| Cathode | Diaphragm | Anode |
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| | | |
| Electrolysis Cell |
| | | |
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2. Electrolysis process:
- The anode (positive electrode) is usually made of carbon and is labeled "Anode" in the diagram.
- The cathode (negative electrode) is also made of carbon and is labeled "Cathode" in the diagram.
- Molten aluminum oxide (bauxite) is filled into the cell and is labeled "Molten Aluminum Oxide."
- The aluminum oxide dissociates into aluminum ions and oxide ions:
2Al₂O₃(l) → 4Al³⁺(l) + 3O²⁻(l)
Anode Diaphragm Cathode
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| |
| Molten Aluminum Oxide |
| |
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3. Electrochemical reactions:
- At the cathode:
- Aluminum ions (Al³⁺) migrate towards the cathode (negative electrode).
- At the cathode, the aluminum ions gain electrons and get reduced to form aluminum metal.
- This reduction reaction can be represented as:
Al³⁺(l) + 3e⁻ → Al(l)
- At the anode:
- Oxide ions (O²⁻) migrate towards the anode (positive electrode).
- At the anode, the oxide ions release electrons and get oxidized to form oxygen gas.
- This oxidation reaction can be represented as:
2O²⁻(l) - 4e⁻ → O₂(g)
4. Overall reaction:
- The overall reaction of the electrolysis of molten aluminum oxide can be represented as:
2Al₂O₃(l) → 4Al(l) + 3O₂(g)
By following these steps, molten aluminum oxide (bauxite) can be electrolyzed, with aluminum metal being formed at the cathode and oxygen gas being formed at the anode.