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

Which gas is produced at the cathode during the electrolysis of sodium chloride solution?

1. Chlorine

2. Hydrogen

3. Oxygen

4. Carbon dioxide

The correct answer is: Hydrogen

During the electrolysis of sodium chloride solution, the process involves the breakdown of sodium chloride (NaCl) into its constituent ions—sodium ions (Na⁺) and chloride ions (Cl⁻)—in an aqueous environment. At the cathode, reduction occurs, which is the gain of electrons. In the presence of water, the hydrogen ions (from the water) will gain electrons at the cathode, leading to the formation of hydrogen gas. Thus, hydrogen gas is produced at the cathode during the electrolysis of sodium chloride solution. This overall reaction can be represented as: \[ 2H_2O + 2e^- \rightarrow H_2 + 2OH^- \] This reaction highlights the reduction of water to produce hydrogen gas. The other options like chlorine, oxygen, and carbon dioxide do not pertain to the cathodic reaction in this specific electrolysis scenario. Chlorine gas is actually produced at the anode, oxygen gas is produced at higher voltages or with other setups, and carbon dioxide does not typically form in this process.