Magnesium is extracted from magnesium oxide (MgO) by electrolysis of molten MgO. The chemical equation for this process is:

A reducing agent is needed because magnesium oxide is an oxide, meaning it has already combined with oxygen. To extract magnesium, we need to reverse this process and remove the oxygen. Electrolysis provides the energy to break the ionic bonds in the molten MgO, allowing the magnesium ions (Mg²⁺) to be reduced to molten magnesium (Mg) at the cathode and oxygen ions (O²⁻) to be oxidized to oxygen gas (O₂) at the anode.

The conditions required for this extraction to occur are:

• Molten State: MgO must be in a molten state. This is because ionic compounds only exist in the molten state when they are heated to a high temperature.
• Electrolysis: The process must be carried out using electrolysis, which involves passing an electric current through the molten MgO.
• Suitable Electrolyte: A suitable electrolyte is required to conduct the electric current. Molten MgO itself acts as the electrolyte.
• Controlled Temperature: The temperature must be carefully controlled to maintain the molten state of MgO and ensure efficient electrolysis.

The extraction of aluminium from purified bauxite involves a process called the Hall-Héroult process. Bauxite is first treated to produce alumina (Al₂O₃). This alumina is then dissolved in molten cryolite (Na₃AlF₆) at a high temperature (around 950-980 °C). Cryolite acts as a solvent, lowering the melting point of alumina significantly, which reduces the energy required for the electrolysis process. Without cryolite, the temperature needed would be prohibitively high.

The electrolytic cell consists of a steel case containing the molten alumina and cryolite mixture. Carbon anodes are suspended in the electrolyte, and the cathode is a steel mesh. When a direct electric current is passed through the mixture, the following reactions occur:

• At the Cathode (Reduction): Al³⁺(l) + 3e^- → Al(l) Aluminium ions are reduced to molten aluminium, which collects at the bottom of the cell.
• At the Anode (Oxidation): 2O^2-(l) → O₂(g) + 4e^- Oxide ions are oxidized to oxygen gas. The carbon anodes are consumed in this reaction.

The carbon anodes need to be regularly replaced because they are oxidized during the electrolysis process. The oxide ions (O^2-) from the electrolyte are oxidized to oxygen gas (O₂) on the anode surface. This continuous oxidation causes the anodes to gradually erode and be consumed. Therefore, they must be replaced periodically to maintain the efficiency of the process.

The reduction of iron(III) oxide (Fe₂O₃) by carbon monoxide (CO) is a key step in the extraction of iron. The reaction can be represented by the following equation:

Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)

This reaction occurs at high temperatures, typically around 2000°C, within the blast furnace. The high temperature is necessary to provide the activation energy required for the reaction to proceed. The presence of carbon monoxide is crucial as it acts as the reducing agent, donating electrons to the iron(III) oxide and causing it to be reduced to iron. The carbon monoxide is produced from the partial combustion of coke within the furnace. The reaction is exothermic, meaning it releases heat, which further contributes to maintaining the high temperature within the blast furnace and driving the reaction forward.