What is electrolysing brine (concentrated NaCl solution) and what products are formed at the electrodes?

What is electrolysing brine (concentrated NaCl solution) and what products are formed at the electrodes?

• A. Cathode: hydrogen gas; Anode: chlorine gas; NaOH remains in solution.
• B. Cathode: chlorine gas; Anode: hydrogen gas; NaOH forms solid.
• C. Cathode: sodium metal; Anode: oxygen gas; water remains.
• D. Cathode: oxygen gas; Anode: chlorine gas; NaCl is deposited.

Answer: (A)

Electrolysing brine uses electricity to drive reactions in a concentrated NaCl solution. At the cathode, water is reduced to hydrogen gas and hydroxide ions: 2H2O + 2e− → H2 + 2OH−. The OH− ions stay in solution with Na+ to form NaOH, so the base remains dissolved. At the anode, chloride ions are oxidized to chlorine gas: 2Cl− → Cl2 + 2e−. So the expected products are hydrogen gas at the cathode, chlorine gas at the anode, and NaOH remaining in solution. The overall reaction is 2NaCl + 2H2O → Cl2 + H2 + 2NaOH.

Electrolysing brine uses electricity to drive reactions in a concentrated NaCl solution. At the cathode, water is reduced to hydrogen gas and hydroxide ions: 2H2O + 2e− → H2 + 2OH−. The OH− ions stay in solution with Na+ to form NaOH, so the base remains dissolved. At the anode, chloride ions are oxidized to chlorine gas: 2Cl− → Cl2 + 2e−. So the expected products are hydrogen gas at the cathode, chlorine gas at the anode, and NaOH remaining in solution. The overall reaction is 2NaCl + 2H2O → Cl2 + H2 + 2NaOH.