Redox Phenomena and Acidity

The medium s acidity may play a part in redox phenomena in several respects. 

In the first instance, depending on its value, the pH can induce the formation of new redox couples. These new couples involve species that do not exist in other ranges of acidity. In such a respect, the pH may simply change the redox couple s nature by modifying the acido-basic status of the Ox or Red form, or both. Finally, even if the redox couple is perfectly defined notably from the acido-basic standpoint, the protonic activity of the medium may greatly change its redox power. 

The example of redox equilibria involving chlorine with the oxidation numbers —1,0, and -K illustrates the influence of the medium s acidity on their course  

In this range, chlorine can be under the oxidation states —1,0, and +1. 

It must be emphasized that even if the oxidation states do not change in this case, the members of the couple do change with the pH value and, therefore, the nature itself of the couple changes. As a result, several standard potentials must be considered. For example, for the couple HC10/C10 , we find (HCIO/CIO ) = 1.51 V, and for the couple C10 /C1 , we find °(C10 /CC) = 1.73 V. 

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