Castner-Kellner’s Process

Introduction

Chlorine plays an important role in industries. Therefore to fulfill the demands, chlorine is manufactured on large scale. It is prepared by the electrolysis of aqueous solution of sodium chloride, this process is knows as Castner-Kellner’s Process and it is carried out in Castner-Kellner’s Cell.

Construction Of Castner-Kellner’s Cell

The Castner-Kellner’s cell consist of a steel tank which contain Hg flows from right to left in the cell and is connected with the negative terminal of the battery therefore it acts as cathode. The cell is filled with saturated aqueous solution of NaCl, which also flows in the same direction as Hg. Some graphite rods are dipped into the solution of NaCl. These rods connected with positive terminal of the battery therefore act as anode as shown in figure.

Figure

Working Of Castner-Kellner’s Cell

When the electric current is passed through the cell. The sodium ion and chloride ion migrates towards their respective electrodes. Chlorine ion moves towards anode, loses its electron and converts into chlorine gas. The free chlorine gas comes out of the tube at the top of the cell. The sodium ion migrates towards cathode gains electrons and converts into sodium metal. The sodium is dissolved in Hg to form sodium amalgum which comes out with the flow of Hg from the cell.

NaCl « Na⁺ + Cl^-

Na⁺ + e^- ® Na⁰  (At cathode)

2Cl ® Cl₂­ + 2e (At anode)