E h

Abstract Redox potential ( E h ) is an intensity measure of the reducing or oxidizing conditions in a system and reflects the tendency of ions or molecules in a solution to donate or accept electrons. It is an easily measured parameter to evaluate water chemistry. However, there is a large discrepancy between theoretical definition and measured E h values, leading to difficulties in correlating the measured E h with specific redox reactions or redox species in water. This is mainly because redox systems in natural environments are seldom at equilibrium, in addition to the presence of multiple redox components and many redox species are not electroactive. Thus, E h measurement only gives a qualitative indication of the electron richness or poorness of a system. If handled carefully by following proper procedures, E h data can indicate the progress of a system toward reduction or oxidation, delineate redox gradients in a stratified system, and assist in further determination of redox reactions. A review and summary of theoretical predictions, measurement, and the applications of E h in aqueous chemistry are presented.