The Castner-Kellner cell process is an electrolytic method for the industrial production of sodium hydroxide, chlorine, and hydrogen from brine. Let's evaluate each statement:
Option A: sodium hydroxide is prepared.
In the Castner-Kellner cell, sodium ions are reduced at the mercury cathode to form sodium amalgam. This amalgam is then reacted with water in a separate decomposer unit to produce sodium hydroxide
(NaOH) and hydrogen gas. So, this statement is correct.
Option B: brine solution is the electrolyte.
The cell uses an aqueous solution of sodium chloride
(NaCl), which is commonly known as brine, as the electrolyte. So, this statement is correct.
Option C: mercury acts as anode and carbon rod acts as cathode.
In the Castner-Kellner cell:
Anode: Graphite (carbon) rods are used as the anode, where chloride ions are oxidized to chlorine gas (
2Cl−(aq)⟶Cl2​(g)+2e−).
Cathode: A flowing layer of mercury acts as the cathode, where sodium ions are reduced to form sodium amalgam
(Na+(aq)+e−⟶Na(. in Hg
)).
Therefore, the statement that mercury acts as the anode and carbon rod acts as the cathode is incorrect. The roles are reversed.
Option D: chlorine gas liberates at anode.
As mentioned above, at the graphite anode, chloride ions are oxidized to produce chlorine gas. So, this statement is correct.
The incorrect statement is C .
The final answer is
C