Redox reactions of selenium

Selenium can exist in four oxidation states Se, Selv, Seu and Se11. Sev occurs as 

Selenious acid, H2Se03, is a weaker acid than selenic acid, H2Se04, with the oxyanion HSe03 being the major Se species at all but extremely acidic or alkaline pH values  

For the pH range from 3 to 9, the only Se and Se species of importance are Se04, HSe03 and Se03. The reduction of Se to Se can thus be described by the following two equations  

The reduction of Selv to elemental Se and Seu can be described by the following two equations  

At very low redox potentials, elemental selenium, Se°, can be reduced to hydrogen selenide gas, H2Se, Sc n. Hydrogen selenide gas can dissolve in water and dissociate to form the anions HSe and Se2-. 

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Redox reactions of selenium could now be measured. A convenient example was the oxidation of selenium bound to sulphur in N-acetylcysteine-selenotrisulphide. Upon... 

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