International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

In electrolysis, which process is primarily used for extracting aluminium?

1. Reduction

2. Oxidation

3. Evaporation

4. Filtration

The correct answer is: Reduction

In the extraction of aluminium through electrolysis, the primary process involved is reduction. During this process, aluminium ions in the molten aluminium oxide (often mixed with cryolite to lower the melting point and improve conductivity) gain electrons to form aluminium metal. In the electrolytic cell, aluminium oxide is broken down into its constituent ions, Al³⁺ and O²⁻. The Al³⁺ ions migrate to the cathode, where they are reduced by gaining electrons (the reduction process), resulting in the formation of aluminium metal. This reaction at the cathode is critical as it is responsible for producing the pure aluminium that is collected during electrolysis. At the anode, oxidation occurs as oxide ions release electrons to form oxygen gas. However, the question specifically asks about the main process used for extraction, which is reduction, as this is where the actual aluminium metal is generated. Other processes mentioned, such as evaporation and filtration, are not relevant to the electrolysis process, as they do not directly contribute to the extraction of aluminium from its oxide.