Molten NaCl Electrolysis:
* Available Ions: Only Na+ and Cl- ions are present.
* Reactions:
* At the cathode (negative electrode): Na+ ions gain electrons to form sodium metal (Na).
* At the anode (positive electrode): Cl- ions lose electrons to form chlorine gas (Cl2).
* Products: Sodium metal (Na) and chlorine gas (Cl2).
Aqueous NaCl Electrolysis:
* Available Ions: Na+, Cl-, H+ (from water), and OH- (from water).
* Reactions:
* At the cathode: Since hydrogen ions (H+) are more easily reduced than sodium ions (Na+), hydrogen gas (H2) is produced.
* At the anode: Since chloride ions (Cl-) are more easily oxidized than hydroxide ions (OH-), chlorine gas (Cl2) is produced.
* Products: Hydrogen gas (H2), chlorine gas (Cl2), and sodium hydroxide (NaOH) is formed in the solution.
Why the Difference?
The key is that in aqueous solution, water molecules dissociate to produce H+ and OH- ions. These ions compete with the ions from NaCl for the electrode reactions. Since H+ is more readily reduced than Na+, and Cl- is more readily oxidized than OH-, the products are different.
Summary:
* Molten NaCl: Only Na+ and Cl- ions are present, leading to the formation of sodium metal and chlorine gas.
* Aqueous NaCl: The presence of H+ and OH- ions from water results in the production of hydrogen gas, chlorine gas, and sodium hydroxide.
