Question

Calculate the oxidation number of ${\text{Fe}}$ in ${\text{F}}{{\text{e}}_3}{{\text{O}}_4}$

Answer 1

Oxidation number of an atom in a compound is determined by calculating the oxidation number of other atoms in the compound. Atoms in their elemental state have zero oxidation number. They are usually written in + or – first then the magnitude is written.

Complete step by step answer: Oxidation number is also known as oxidation state. When hydrogen is combined with non-metal, its oxidation number is $+ 1$. When combined with metal, its oxidation number is $- 1$.
Oxygen has an oxidation state $- 2$ but exceptions are there.
When oxidation numbers in a neutral compound are added, we get the value zero.
In a polyatomic ion, the sum of oxidation numbers is equal to the charge on the ion.
${\text{F}}{{\text{e}}_3}{{\text{O}}_4}$ does not have any charge on it. Thus it is a neutral molecule. Therefore the sum of oxidation numbers of iron and oxygen is equal to zero. There are three iron and 4 oxygen atoms.
Total oxidation number of the neutral compound ${\text{F}}{{\text{e}}_3}{{\text{O}}_4}$ is zero.
i.e. $3 \times$ oxidation number of iron $+ 4 \times$ oxidation number of oxygen $= 0$
Oxidation number of oxygen is $- 2$
We have to calculate the oxidation number of iron.
Let the oxidation number of iron be x.
Therefore, $3{\text{x}} + 4 \times - 2 = 0$
$3{\text{x}} - 8 = 0$
3{\text{x}} = 8 \\\ {\text{x}} = \dfrac{8}{3} \\\
Therefore the oxidation number of iron is $\dfrac{8}{3}$

Additional information:
Oxidation numbers are used to decide whether an element gets reduced or oxidized by checking its oxidation number. In a reaction, if the oxidation number of an element gets decreased from reactants to product, then it is a reduction reaction. If it is vice versa, it is an oxidation reaction.

Note: Oxidation number is the number of electrons an atom gains or loss to form a chemical bond. Neutral substances have zero oxidation number. E.g. ${{\text{P}}_4}$, ${{\text{S}}_8}$, ${{\text{O}}_2}$. Simple ions have oxidation number which is equal to the charge on the ion.