Electrolysis of Molten Sodium Chloride

Electrolysis of the ionic compound Sodium Chloride is commonly carried out to obtain Sodium metal. As Sodium is a highly reactive metal, it does not commonly exist as its atom but usually in compounds, like Sodium Chloride, otherwise known as salt. The electric current in this setup are the ions and the electrons in the anode/cathode and the external circuits.


Since ionic compounds must be in their molton or aqueous forms before they can be electrolyzed, sodium chloride is first heated strongly till it melts. A source of direct current is connected to  a pair of inert electrodes (for instance, Carbon) and placed in a solution of molten sodium chloride. The ions are free to move in molten state, and the sodium cations flow towards the cathode while the chlorine anions flow towards the anode.  The cathode is negatively charged as electrons are pushed into it by the battery while the anode is positively charged as electrons leave the anode. 


At the cathode: The sodium cations are discharged as they take electrons from the negatively charged electrodes to become sodium atoms.  Therefore, sodium ions are reduced at the cathode to form sodium atoms.

Ionic half equation - Reduction at the cathode:

Na+(aq) + e-  Na(s)

 Since sodium is lighter relative to chlorine gas, chloride anions and water, it floats to the surface of the molten sodium chloride and produces exothermic reactions when it reacts with atmospheric gas. 


At the anode: Chlorine anions that collide with the anode are oxidised to form chlorine atoms. 
Ionic half equation - Positive electrode (anode): Cl^-(l) Cl(l) +  e^-

Chlorine atoms combine to form chlorine gas, a diatomic molecule. A color change is observed during the electrolysis of Sodium Chlorine, as a yellow-green gas can be seen at the anode, which is Chlorine gas. 

Ionic equation: 2Cl(l) Cl₂ (g)

Combining the two:

Electrolysis of NaCl:
	Cathode (-):		Na+ + e-  Na
	Anode (+):		2 Cl-  Cl2 + 2 e-

Overall chemical equation: 2 NaCl(l)2 Na(l) + Cl₂(g)




Similarly, other molton ionic compounds which are electrolysed will cause the metal to be produced at the cathode and the non-metal at the anode through a redox reaction. Examples of such molten electrolytes include Sodium Iodide (NaI) and Hydrochloric Acid (HCl).