Process of Electrolysis of Molten Salts

• Selection of Molten Salt: The choice of molten salt depend on the desired reaction and the elements or compounds to be produced.
• Setup of Electrolytic Cell: An electrolytic cell is assembled with a container capable of withstanding high temperatures to hold the molten salt. Two electrodes, typically made of inert materials like graphite or platinum, are immersed in the molten salt. These electrodes serve as the cathode ( negative electrode) and anode (positive electrode).
• Application of Electric Current: An external power source, usually a direct current(DC) power supply, is connected to the electrodes. The positive terminal of the power supply is connected to the anode, while negative te3rminal is connected to the cathode. This setup allows for the flow of electrons from the cathode to the anode through the molten salt.
• Redox Reactions at Electrodes: As the electric current passes though the molten salt, cations migrate towards the cathode, while anions migrate towards anode. At the cathode, reduction reactions occur, leading to the deposition of metal or the formation of other reduced species. At the anode, oxidation reactions take place, resulting in the formation of non-metal or other oxidized species.
• Product Formation: The products of electrolysis depend on the composition of the molten salt and the specific reactions occurring at the electrodes.
• Collection and Processing of Products: The products of electrolysis can be collected and further processed according to their intended applications. This may involve purification, refining or additional chemical reactions to obtain the desired final products.

Electrolysis of Sodium Chloride

The electrolysis of sodium chloride (NaCl) is a process that occurs when an electric current is passed through a molten or aqueous solution of sodium chloride. The process involves the decomposition of the compound into its constituent elements, sodium (Na) and chlorine (Cl₂) through the following reactions:

• At the cathode (negative electrode):

2Na⁺ + 2e^– → 2Na

Sodium ions gain electrons (reduction) and form sodium metal, which may either float to the surface or remain in solution as sodium ions.

• At the anode (positive electrode):

2Cl^– → Cl₂ + 2e^–

Chloride ions lose electrons (oxidation) and form chlorine gas.

The overall reaction can be represented as:

2NaCl (l) → 2Na (s) + Cl₂ (g)

Redox Reactions for Electrolysis of Molten Salts

In the electrolysis of molten salts, redox reactions occur at the electrodes. Let’s consider some examples:

• Electrolysis of Molten Sodium Chloride (NaCl):

At the cathode: 2Na⁺ + 2e^– → 2Na

At the anode: 2Cl^– → Cl₂ +2e^–

Overall reaction:

2NaCl (l) → 2Na (s) + Cl₂ (g)

• Electrolysis of Molten Aluminum Oxide (Al₂O₃):

At the cathode: Al₃⁺ + 3e^– → Al

At the anode: 2O^2- → O₂ + 4e^–

Overall reaction:

2Al₂O₃ (l) → 4Al (l) + 3O₂ (g)

• Electrolysis of Molten Calcium Chloride (CaCl₂):

At the cathode : Ca²⁺ + 2e^– → Ca

At the anode: 2Cl^– → Cl₂ + 2e^–

CaCl₂ (l) → Ca(s) + Cl₂ (g)

Electrolysis of Aluminum as an Example

The electrolysis of aluminum involves the extraction of aluminum from aluminum oxide ( Al₂O₃) dissolved in molten cryolite (Na₃AlF₆).

Cathode: Each aluminum ions gains three electrons to form aluminum metal. This reduction reaction occurs at the cathode, where the aluminum ions are attracted to.

2Al³⁺ + 3e^– → Al

Anode: Oxygen ions lose four electrons to form oxygen gas. This oxidation reaction reaction occurs at the anode, where the oxygen ions migrate due to the electric field.

2O^2- → O₂ + 4e^–

Overall Reaction:

2Al₂O₃ (l) → 4Al (l) + 3O₂ (g)

This reaction indicates the reduction of aluminum ions to aluminum metal at the cathode and the oxidation of oxygen ions to oxygen gas at the anode. This method is essential in the industrial production of aluminum, which is widely used in various applications due to its lightweight, strength and the resistance to corrosion.

Electrolysis of molten salt is a crucial electrochemical process with applications ranging from metal extraction to energy storage and industrial synthesis. Molten salts, characterized by their high ionic conductivity, serve as efficient electrolytes in this process, enabling the dissociation of salts into their constituent ions upon applying an electric current. This controlled decomposition allows for the extraction of metals, synthesis of chemicals, and other transformative reactions essential to various industries.