ABSTRACT
Oxidation-reduction (redox) reactions are those involving changes of oxidation states of reactants. Such reactions are easiest to visualize as the transfer of electrons from one species to another. For example, soluble cadmium ion, Cd2+, is removed from wastewater by reaction with metallic iron. The overall reaction is
Cd Fe Cd Fe 2 2+ ++ +→ (4.1)
This reaction is the sum of two half-reactions, a reduction half-reaction in which cadmium ion accepts two electrons and is reduced,
Cd 2 Cd 2+ −+ e → (4.2)
and an oxidation half-reaction in which elemental iron is oxidized:
Fe Fe 2 2→ + −+ e (4.3)
When these two half-reactions are added algebraically, the electrons cancel on both sides and the result is the overall reaction given in Equation 4.1.
