Question

The chlor-alkali process ⁵⁴in which seawater is electrolyzed to make CI₂ andNaOH, is the second most important commercial electrolysis, behindAIproduction.

Anode: ${\mathbf{CI}}^{\mathbf{-}}\mathbf{}\mathbf{\to }\frac{\mathbf{1}}{\mathbf{2}}{\mathbf{CI}}_{\mathbf{2}}\mathbf{+}{\mathbf{e}}^{\mathbf{-}}$

HgCathode:${\mathbf{Na}}^{\mathbf{+}}\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{+}{\mathbf{e}}^{\mathbf{-}}\mathbf{}\mathbf{\to }\mathbf{NaOH}\mathbf{+}\frac{\mathbf{1}}{\mathbf{2}}{\mathbf{H}}_{\mathbf{2}}$

The Nafion membrane (page 421) used to separate the anode and cathode compartments resists chemical attack. Its anionic side chains permit conduction ofNa⁺ , but not anions. The cathode compartment contains pure water, and the anode compartment contains seawater from which Ca²⁺ and Mg²⁺ have been removed. Explain how the membrane allows NaOH to be formed free ofNaCI.

Short answer

The Nafion membrane allowsNaOH to be formed free of NaCI because ${\mathrm{OH}}^{-}$ionsproduced by the cathode and ${\mathrm{CI}}^{-}$ions produced by anode cannot cross the membrane, while the Na⁺ ions can. Na⁺ crosses from anode to cathode to keep charge balance.

Step-by-step solution

Fundamentals of electrolysis

• Electrolysis is a fundamental process in chemistry that involves the breakdown of an electrolyte (a solution) and the creation of positive and negative ions.
• This is the underlying concept of electrolytic cells.
• The procedure may appear hard, yet it is as simple as a walk in the park.

Explanation

• The Nafion membrane allows NaOH to be formed free of NaCl because ${\mathrm{OH}}^{-}$ions produced by the cathode and ${\mathrm{CI}}^{-}$ions produced by anode cannot cross the membrane, while the Na⁺ ions can.
• Na⁺ crosses from anode to cathode to keep charge balance.