Explain the following in terms of the gain of oxygen with two examples each.

(a) Oxidation

(b) Reduction

(a) In a chemical reaction, when the oxygen is added to the element to form its respective oxide it is the element being oxidised. Example:

4Na(s) + O2(g) → 2Na2O(s)

H2S + O2 → H2O + SO2

(b) In a chemical reaction, when the oxygen is removed from the compound, then it is said to be reduced. Example:

CuO(s) + H2(g) → Cu(s) + H2O(l)

2HgO → 2Hg + O2