ABSTRACT
The terms oxidation and reduction are very important in chemistry, and you will frequently encounter them in studies of the environment. ‘Oxidation’ suggests that oxygen is involved, and in fact the term was once used only to refer to chemical reactions involving the addition of oxygen to a substance. In contrast, reduction was used to refer to the loss of oxygen from a substance. This usage is still commonly employed: after all, oxygen is a very abundant element and it reacts readily with many of the elements. Nearly all the familiar minerals, and many gases contain oxygen. Environments may be described as oxidizing (or aerobic) if free oxygen (O2) is present, and reducing (or anaerobic) if oxygen is absent. Similarly, we use the expressions aerobic and anaerobic metabolism depending on whether or not oxygen is involved, and aerobic and anaerobic organisms depending on whether or not they use oxygen (see 34.3.3). The use of the terms ‘oxidation’ and ‘reduction’ was later extended to cover hydrogen. A substance is said to be oxidized if it loses hydrogen, and reduced if it acquires hydrogen.
