JAMB - Chemistry (2025 - No. 102)
What is the product obtained at the anode in the electrolysis of concentrated sodium chloride using graphite electrode?
Chlorine gas
oxygen gas
water vapour
hydrogen gas
คำอธิบาย
In the electrolysis of a concentrated sodium chloride solution (brine) using inert graphite electrodes, both chloride ions (Cl\(^-\)) and hydroxide ions (OH\(^−\)) (from the water) are attracted to the positive anode. Although, based on standard electrode potentials, the oxidation of hydroxide ions to oxygen gas should be preferred, the high concentration of chloride ions and the overpotential for oxygen evolution means that chloride ions are preferentially discharged to produce chlorine gas (Cl\(_2\)) at the anode.
The reaction is : 2Cl\(^-\) → Cl\(_2\) + 2e\(^-\)
The correct option is A. Chlorine gas.