Sodium ions, discharge standard potential

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

The reversible potential of the sodium amalgam electrode, considering an amalgam concentration of 0.2 wt% sodium and the already mentioned sodium concentration, amounts to —1.78 V (the difference to the Na/Na+-standard potential —2.71 V is due to the fact that in the case of amalgam the discharged sodium ions must not be incorporated into a metallic structure). 

Cathode Reactions. The standard potential of the hydrogen-liberating reaction is 0 V, which is considerably higher than the potential for the formation of 0.2 wt % sodium amalgam, -1.868 V. However, hydrogen is not liberated at the mercury surface because the reaction is kinetically inhibited. Mainly sodium ions are discharged. At the sodium chloride concentrations used, the reversible potential is reduced by ca. 0.2 V. 

Chloride ions will be discharged at a platinum, graphite or magnetite anode from saturated neutral solutions of sodium or potassium chloride rather than hydroxyl ions although at equilibrium conditions it should be the very opposite, as the reversible deposition potential (reduction potential) of oxygen in neutral solution is much lower ) (7Eoh- i o2. Pt = 0.815 V at 25 °C) than the standard... 

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