The Electrolytic Decomposition of Molten Salts

The discovery of ions resulted from the experimental investigations of the interaction of an electric current with chemical substances. These investigations were begun early in the nineteenth century, and were carried on effectively by Michael Faraday (1791-1867) in the period around 1830. 

Molten sodium chloride (the salt melts at 80 TC) conducts an electric current, as do other molten salts. During the process of conducting the current a chemical reaction occurs the salt is decomposed. If two electrodes (carbon rods) are dipped into a crucible containing molten sodium chloride and an electric potential, from a battery or generator, is applied, metallic sodium is produced at the cathode and chlorine gas at the anode. Such electric decomposition of a substance is called electrolysis. 

Molten sodium chloride, like the crystalline substance, consists of equal numbers of sodium ions and chloride ions. These ions are very stable, and do not gain electrons or lose electrons easily. Whereas the ions in the crystal are firmly held in place by their neighbors, those in the molten salt move about with considerable freedom. 

The preceding statement describes the mechanism of the conduction of the current through the liquid. We must now consider the way in which the current passes between the electrodes and the liquid that is, we consider the electrode reactions. 

The process that occurs at the cathode is this sodium ions, attracted to the cathode, combine with the electrons carried by the cathode to form sodium atoms that is, to form sodium metal. The cathode reaction accordingly is 

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