Rules In oxidation number

1. The oxidation number of all elements in the free state is zero e.g. Na, CL₂ etc.
2. The oxidation number of a simple ion has the same sign as the change of the Ion.

EXAMPLE:

Calculate the oxidation of carbon In CaCO₂

Solution

Ca = +2, O = 2
∴Ca²⁺; O^-2
∴2 x 1 +x – 2×3 = 0
2 +x – 6 = 0
x – 4 = 0
x = 4

The oxidation number of carbon In CaCO₃ is 4.