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

Which equation represents the formation of chlorine gas during electrolysis?

1. Cl⁻ + e⁻ -> Cl₂

2. 2Cl⁻ -> Cl₂ + 2e⁻

3. Cl + 2e⁻ -> Cl₂

4. Cl₂ + 2e⁻ -> 2Cl⁻

The correct answer is: 2Cl⁻ -> Cl₂ + 2e⁻

In the process of electrolysis where chlorine gas is formed, the creation of chlorine gas (Cl₂) from chloride ions (Cl⁻) occurs through a specific half-reaction. The correct representation is that two chloride ions lose their electrons and combine to form one molecule of chlorine gas, resulting in the release of two electrons in the process. When chloride ions undergo electrolysis at the anode, they are oxidized. This reaction involves two chloride ions combining, which can be expressed as \(2Cl^− \rightarrow Cl_2 + 2e^−\). This indicates that two moles of chloride ions lose two moles of electrons to form one mole of chlorine gas. The other formations proposed in the other options do not accurately depict the process of chlorine gas being generated from chloride ions, which is why they are not valid representations of the formation of chlorine gas through electrolysis. Understanding the redox processes involved helps clarify why this particular equation is the correct choice and highlights the stoichiometry of the reaction as well.