Electrolytic cells pure molten salts, electrolysis

Electrolysis of Molten Salts and the Industrial Production of Sodium Many electrolytic applications involve isolating a metal or nonmetal from a molten binary ionic compound (salt). Predicting the product at each electrode is simple if the salt is pure because the cation will be reduced and the anion oxidized. The electrolyte is the molten salt itself, and the ions move through the cell because they are attracted by the oppositely charged electrodes. 

The first, and now obsolete, industrial processes for producing raw sodium metal were based on the carbon reduction of sodium carbonate or sodium hydroxide. The first industrial production of pure sodium metal was performed by molten-salt electrolysis of the pure sodium hydroxide, NaOH, in so-caUed Castner cells. Most modern processes for the production of sodium now involve molten-salt electrolysis of highly pure sodium chloride. Actually, since 1921, when the process was invented by J.C. Downs, the electrolysis has been performed in Downs electrolytic cells at the DuPont de Nemours Canadian facilities at Niagara Falls, Ontario, Canada. The electrolytic cell consists of four cylindrical anodes made of graphite surrounded at the bottom of the cell by steel cathodes, and a fine steel mesh acts as a separator between anodic and cathodic compartments. Each cell contains a batch of 8 tonnes of a molten-salt mixture with the following chemical composition NaCl (28 wt.%), CaCl (26 wL%), and BaClj (46 wt.%). 

An electrolytic cell uses electrical energy to drive a nonspontaneous reaction. Oxidation occurs at the anode and reduction at the cathode, but the direction of electron flow and the charges of the electrodes are opposite those in voltaic cells. In electrolysis of a pure molten salt, the metal cation is reduced at the cathode, and the nonmetal anion is oxidized at the anode. 

Electrolysis, the splitting (lysing) of a substance by the input of electrical energy, is often used to decompose a compound into its elements. Electrolytic cells are involved in key industrial production steps for some of the most commercially important elements, including chlorine, copper, and aluminum. The first laboratory electrolysis of H2O to H2 and O2 was performed in 1800, and the process is still used to produce these gases in ultrahigh purity. The electrolyte in an electrolytic cell can be the pure compound (such as H2O or a molten salt), a mixture of molten salts, or an aqueous solution of a salt. The products obtained depend on several factors, so let s examine some actual cases. 

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