Question

Find the oxidation number of $$\text{Fe}$$ in $${\text{K}}_2\text{Fe}{\text{O}}_{\text{4}}$$.

Answer 1

Hint: Oxidation number is the total number of electrons gained or lost by an atom in a molecule, to form a chemical bond. The oxidation number of potassium is +1 whereas the oxidation number of oxygen is -2. In a neutral molecule, the sum of the oxidation numbers of all the elements is zero.

Complete step by step answer:
Oxidation state is also known as the oxidation number. It is the total number of electrons either gained or lost by an atom to form a chemical bond with another atom.
Let X be the oxidation number of $$\text{Fe}$$ in $${\text{K}}_2\text{Fe}{\text{O}}_{\text{4}}$$
The oxidation number of potassium is +1 whereas the oxidation number of oxygen is -2. In a neutral molecule, the sum of the oxidation numbers of all the element is zero. In a polyatomic ion, the sum of the oxidation numbers of all the elements is equal to the charge on the ion.
Calculate the oxidation number of $$\text{Fe}$$ in $${\text{K}}_2\text{Fe}{\text{O}}_{\text{4}}$$
$$\begin{gathered} {\text{K}}_2\text{Fe}{\text{O}}_{\text{4}} \\ \text{2}\left(\text{ + 1}\right)\text{ + X + 4}\left(-2\right)\text{ = 0} \\ \text{2 + X }-\text{ 8 = 0} \\ \text{X }-\text{ 6 = 0} \\ \text{X = + 6} \end{gathered}$$
Hence, the oxidation number of $$\text{Fe}$$ in $${\text{K}}_2\text{Fe}{\text{O}}_{\text{4}}$$ is +6.
In the above calculation, the oxidation number of potassium is multiplied with 2 as there are two potassium atoms. Similarly, the oxidation number of oxygen is multiplied with 4 as there are four oxygen atoms.

Additional Information: Metals such as potassium and iron have positive oxidation numbers and non-metals such as oxygen have negative oxidation numbers.

Note: Oxidation number represents general distribution of electrons. Oxidation number gives the total number of electrons gained or lost by an atom to form a chemical bond. Thus, when a neutral potassium atom loses one electron to form cation, it attains oxidation number of +1. When a neutral oxygen atom gains two electrons to form oxide anion, it attains an oxidation number of -2.