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

What indicates that the reaction Al³⁺ + 3e⁻ -> Al is a reduction reaction?

1. Al³⁺ loses electrons

2. Al gains electrons

3. Both species are neutral

4. There is a heat release

The correct answer is: Al gains electrons

The indication that the reaction Al³⁺ + 3e⁻ -> Al is a reduction reaction primarily lies in the gain of electrons by the aluminum ion. In a reduction reaction, a species undergoes a decrease in oxidation state, which is achieved through the acquisition of electrons. In this case, the aluminum ion (Al³⁺) gains three electrons (3e⁻), transforming into neutral aluminum (Al). This process exemplifies reduction because it reduces the positive charge of Al³⁺ to a neutral state. The increase in electron count signifies that the aluminum ion has been reduced in terms of its oxidation number, moving from +3 to 0. This fundamental principle is crucial to understanding redox (reduction-oxidation) reactions in chemistry, where one species is reduced by gaining electrons while another is oxidized by losing electrons.