Substances Which Are Both Oxidizing and Reducing Agents
Water We have seen that some oxidizing agents, such as fluorine, can oxidize water to oxygen. There are also some reducing agents, such as lithium, which can reduce water to hydrogen. In terms of redox, water behaves much as it did in acid-base reactions, where we found it to be amphiprotic. In the presence of a strong electronA negatively charged, sub-atomic particle with charge of 1.602 x 10-19 coulombs and mass of9.109 x 1023 kilograms; electrons have both wave and particle properties; electrons occupy most of the volume of an atom but represent only a tiny fraction of an atom's mass. donor (strong reducing agent), water serves as an oxidizing agent. In the presence of a strong electron acceptor (strong oxidizing agent), water serves as a reducing agent. Water is rather weak as an oxidizing or as a reducing agent, however; so there are not many substances which reduce or oxidize it. Thus it makes a good solventThe substance to which a solute is added to make a solution. for redox reactions. This also parallels water’s acid-base behavior, since it is also a very weak acid and a very weak base.
Hydrogen peroxide, H2O2 In this moleculeA set of atoms joined by covalent bonds and having no net charge. the oxidation number for oxygen is –1. This is halfway between O2(0) and H2O(–2), and so hydrogen peroxide can either be reduced or oxidized. When it is reduced, it acts as an oxidizing agent:
H2O2 + 2H+ + 2e– → 2H2O
When it is oxidized, it serves as a reducing agent:
H2O2 → O2 + 2H+ + 2e–
Hydrogen peroxide is considerably stronger as an oxidizing agent than as a reducing agent, especially in acidic solutions.