Oxidation

You can use three definitions for oxidation:

✓ The loss of electrons

✓ The gain of oxygen

✓ The loss of hydrogen

Because I typically deal with electrochemical cells, I normally use the definition that describes the loss of the electrons. The other definitions are useful in processes such as combustion and photosynthesis.

Loss of electrons

One way to define oxidation is with the reaction in which a chemical substance loses electrons in going from reactant to product. For example, when sodium metal reacts with chlorine gas to form sodium chloride (NaCl), the sodium metal loses an electron, which chlorine then gains. The following equation shows sodium losing the electron:

Na_(s) → Na⁺ + e^–

When it loses the electron, chemists say that the sodium metal has been oxidized to the sodium cation.

Reactions of this type are quite common in electrochemical reactions, reactions that produce or use electricity.

Gain of oxygen

In certain oxidation reactions, it’s obvious that oxygen has been gained in going from reactant to product. Reactions where the gain of oxygen is more obvious than the gain of electrons include combustion reactions (burning) and the rusting of iron. Here are two examples:

C_(s) + O_2(g) → CO_2(g) (burning of coal)

2 Fe_(s) + 3 O_2(g) → 2 Fe₂O_3(s) (rusting of iron)

In these cases, chemists say that the carbon and the iron metal have been oxidized to carbon dioxide and rust, respectively.

Loss of hydrogen

In other reactions, you can best see oxidation as the loss of hydrogen. Methyl alcohol (wood alcohol) can be oxidized to formaldehyde:

CH₃OH_(l) → CH₂O_(l) + H_2(g)

In going from methanol to formaldehyde, the compound goes from having four hydrogen atoms to having two hydrogen atoms.