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

What is produced at the positive electrode during the electrolysis of sodium chloride solution?

1. Hydrogen gas

2. Chlorine gas

3. Sodium hydroxide

4. Chlorine ion

The correct answer is: Chlorine gas

During the electrolysis of sodium chloride solution, the process involves the breakdown of sodium chloride (NaCl) into its constituent ions in water: sodium ions (Na⁺) and chloride ions (Cl⁻). At the positive electrode, known as the anode, oxidation reactions take place. Chloride ions are oxidized to form chlorine gas. This is a key aspect of the electrolysis process, as it illustrates how halide ions contribute to the production of elemental gases when subjected to electrolysis. The production of chlorine gas at the anode is further supported by the observation that chlorine has a higher tendency to be oxidized when compared to water, which can also produce oxygen gas. The specific conditions of the electrolysis of sodium chloride solution favor the formation of chlorine gas, leading to its dominance as the product at the positive electrode. In summary, the correct answer reflects the chemical behavior of chloride ions during electrolysis, resulting in chloride ions being oxidized to chlorine gas at the positive electrode. This understanding is vital to grasping the fundamentals of electrolysis and the behavior of ionic solutions in electric fields.