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 \[{{\text{K}}_2}{\text{Fe}}{{\text{O}}_{\text{4}}}\]
\[{{\text{K}}_2}{\text{Fe}}{{\text{O}}_{\text{4}}} \\
{\text{2}}\left( {{\text{ + 1}}} \right){\text{ + X + 4}}\left( { - 2} \right){\text{ = 0}} \\
{\text{2 + X }} - {\text{ 8 = 0}} \\
{\text{X }} - {\text{ 6 = 0}} \\
{\text{X = + 6}} \\\]
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.