Chapter 17: Q8P (page 427)

The chlor-alkali process ⁵⁴in which seawater is electrolyzed to make CI₂ andNaOH, is the second most important commercial electrolysis, behindAIproduction.
Anode: ${CI}^{-} \to \frac{1}{2} {CI}_{2} + e^{-}$
HgCathode: ${Na}^{+} + H_{2} O + e^{-} \to NaOH + \frac{1}{2} H_{2}$
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

Expert verified

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