Electrolysis of Molten Sodium Chloride

In this, we discuss the electrolysis of molten sodium chloride by understanding the electrochemical cells and the process of electrolysis in general. Electrochemistry is the study of the movement of electrons from one electrode to another by oxidation or reduction. Electrochemistry deals with the relation between electricity and chemical reactions.

Electrochemical cells

An electrochemical cell is a cell in which transferring of charge of one electrode to another electrode is achieved by the movement of ions or electrons. 

The electrochemical cell consists of two electrodes, namely anode and cathode. A cathode is an electrode in which a reduction reaction occurs, and an oxidation reaction will occur in the anode.

The electrodes are kept in an electrolytic solution to carry out the electrolysis process.

Electrolysis 

An electric current is made to pass on the electrodes, which are kept in an electrolytic solution. When the current passes in an electrolytic solution, either there will be a loss of electrons (i.e. oxidation) or a gain of electrons (i.e. reduction). This process of transferring ions from one electrode to another is called electrolysis.

Electrolysis is a non-spontaneous process. The main purpose of electrolysis is to separate a particular substance from the original compound. By this process of electrolysis, many new elements have been discovered. Even today, researchers are discovering new elements with the help of this electrolytic process.

There are many types of processes included in electrolytic processes. Some common processes are electrolytic refining, electrosynthesis, and chloro alkali. 

Electrolysis is mainly used in the pharmaceutical industry and other industries to purify metals extracted from ores, electroplating. Metallic sodium and chlorine gas, hydrogen, and oxygen are produced by performing various reactions, which are used for any commercial purposes.

Electrode Potential

The potential difference between the electrode present in an electrochemical cell and the electrolyte is called electrode potential. Eo denotes it. The oxidation and reduction in the cell are measured in volts: oxidation potential (Eoox ) and reduction potential (Eored).

Electrolysis of Molten Sodium Chloride

The electrolysis of molten sodium chloride means the electrolysis reaction in liquid or fused sodium chloride.

The electrolysis of molten sodium chloride is carried out to produce metallic sodium and chlorine gas.

The Down cell process carries out the electrolysis of molten sodium chloride. The down process is carried out at the industrial level. The molten sodium chloride consists of free sodium ions(Na+) and free chlorine ions (Cl-).

The overall simple reaction could be written as,

           2NaCl(l) → 2Na(l) +Cl2(g)

If the above reaction takes place in the reversible form, we will obtain the NaCl. This reaction is carried out at a temperature of approximately 800°C. To obtain the liquid sodium metal, the liquid sodium chloride will undergo a reduction reaction at approximately 98°C to obtain the liquid sodium metal.  

The above diagram represents the down cell in which the electrolysis of molten sodium metal takes place. The density of liquid sodium is lesser than that of liquid sodium chloride. Thus sodium would float on top with melt. The iron-capped cylinders collect it. These cylinders surround the cathode. The chlorine gas is collected in the cone, which is shown inverted in the diagram above the anode. An iron screen separates the cathode and anode to prevent mixing liquid sodium and chlorine gas.

The electrolysis process of molten sodium chloride occurs through the following steps:   

•  The positively charged Na+ ions are attracted towards the cathode as the cathode is a negatively charged electrode.

• The Na+ ions being positively charged negatively charged electrons from the cathode attract it. So, it takes up electrons from the cathode. Thus the reduction reaction takes place. This reduction reaction taking place at the cathode is well understood from the following equation, 

                                  Na+(l) + e– → Na(l)

• The Cl- being negatively charged, it loses an electron, and it is oxidised to form chlorine (Cl2)gas. The following electrochemical reaction understands this oxidation reaction that takes place in the anode:

                            2Cl- (l) → Cl2(g) + 2e- (oxidation)

The overall reaction that takes place in the electrochemical cell is written as :

   Na +(l) + e- → Na(l) (reduction) Eo = -1.4V

   2Cl- (l) → Cl2(g) +2e- (oxidation) Eo = -2.7V 

   Na+(l) + 2Cl- (l) → Na(l) + Cl2(g) Eocell = -4.1V

We understood from the above electrochemical reaction that there must be about 4V current needed to produce chlorine gas. 

This process is carried out at extremely high temperatures so that the electrodes can conduct electricity, and the solid metal will melt to liquid form, which is required for this process.

This method of electrolysis of molten sodium chloride is the major and widely used reaction to produce chlorine gas. This reaction is the only way to obtain pure chlorine gas. As we all know, the chlorine gas produced is used as disinfectants in cleaning and swimming pools.  

CONCLUSION           

In this article, we discussed electrochemistry. Electrochemistry deals with electricity and the chemical reaction electrolysis process that is carried out in molten sodium chloride. This article will help answer the electrolysis of molten sodium chloride questions that commonly arise.