Question

What is the relation between Standard reduction potential and reaction with water?

Answer 1

Oxidation and reduction (redox) reactions are very important in drinking water. Oxidation-reduction potential (ORP) measurements reflect the redox state of water. Redox measurements are not widely made by drinking water utilities in part because they are not well understood. The objective of this study was to determine the effect of oxidant type and concentration on the ORP of carbonate buffered water as a function of pH. Oxidants that were studied included: chlorine, monochloramine, potassium permanganate, chlorine dioxide, and oxygen. ORP decreased with increasing pH, regardless of the oxidant type or concentration. ORP increased rapidly with increasing oxidant dosage, particularly at lower concentrations. Differences in the redox potentials of different oxidant systems were also observed. Waters that contained chlorine and chlorine dioxide had the highest ORPs. Tests also revealed that there were inconsistencies with redox electrode measurements. In the standard Zobell reference solution, two identical redox electrodes had nearly the same reading, but in test waters the readings sometimes showed a variation as great as 217.7 mV.