One of the most important types of reactions and the focus of this chapter is the Reduction-Oxidation reaction more commonly known as Redox Reactions. Redox reactions are simultaneously reactions in which both oxidation and reduction occurs at the same time. Understanding the principles of redox reactions enable chemists to use them towards important applications such as electrolysis. In order to understand redox reaction, we must first understand the difference between oxidation and reduction, and then figure out what is being oxidised and what is being reduced.

Oxidation occurs by:

-The loss of electrons

-The gaining of oxygen, example MgO_{(s )} + O_(g) → 2MgO_(s)

-The loss of hydrogen

-An increase in the oxidation state, example +1 to +2

Reduction occurs by:

-The gaining of electrons

_–The loss of oxygen  CuO_(s) +H _(g) → Cu_(s) + H₂ O_(l)

-The gaining of hydgogen

-A decrease in the oxidation state +3 to +2

An easy way to identify which substance is being oxidised and which substance is being reduced is the use of the acronym OILRIG – Oxidation Is Lose, Reduction is Gain. When a substance gains electrons it is reduced and when a substance loses electrons it is oxidised.

Exercise

State whether oxidation or reduction occurs in each reaction:

Sn²⁺ -2e-   →    Sn⁴⁺

Cu²⁺ +2e-     →     Cu(s)

Zn(s) -2e-   →   Zn²⁺