Effect of complexing agents on redox potential

Both Fe and Fe can form complexes with species other than water or OH . Com-plexation can cause marked changes in the electrode potential of the two oxidation states. The difference in standard single potentials between the hydrated and the complexed ions is given by. 

The standard electrode potentials, E°(V) for some chelates of the Fe /Fe redox couple areas follows o-phenanthroline, 1.20 2,2 -bipyridyl 1.096 water, 0.77 cyanide, 0.10 oxalate, -0.01 and 8-hydroquinone, -0.15 (Latimer, 1952). In the case of bipyridyl 

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