Question

Oxidation number of ${\text{Fe}}$ in ${{\text{K}}_{\text{3}}}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]$ is:

Answer 1

Hint: The number which is assigned to an element in the chemical formula is known as the oxidation number. The oxidation number represents the number of electrons gained or lost by the atom of that element in the chemical compound.

Complete step by step answer:
We are given a complex ${{\text{K}}_{\text{3}}}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]$. We have to calculate the oxidation number of the ${\text{Fe}}$ atom in this complex.
There are two ligands as follows:
${\text{K}}$ is a positive ligand. Thus, the charge on ${\text{K}}$ ligand is $ + {\text{1}}$.
${\text{CN}}$ is a negative ligand. Thus, the charge on ${\text{CN}}$ ligand is $ - 1$.
There is no charge on the complex. Thus, the complex is neutral.
Consider that the charge on the ${\text{Fe}}$ is x.
Thus,
$\left( {{\text{3}} \times {\text{O}}{\text{.N}}{\text{. of K}}} \right) + \left( {{\text{O}}{\text{.N}}{\text{. of Fe}}} \right) + \left( {{\text{6}} \times {\text{O}}{\text{.N}}{\text{. of CN}}} \right) = {\text{Charge on the complex}}$
$\left( {3 \times 1} \right) + \left( x \right) + \left( {6 \times - 1} \right) = {\text{0}}$
$\Rightarrow x = + 6 - 3$
$x = + 3$

Thus, the oxidation number of ${\text{Fe}}$ in ${{\text{K}}_{\text{3}}}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]$ is $ + 3$.

Additional Information:
Potassium ferricyanide has various application:
Potassium ferricyanide is used in blueprint drawing and photography.
Potassium ferricyanide is an oxidising agent and is used in the bleaching process to remove silver from colour positives and negatives.
Potassium ferricyanide is used to harden iron and steel.
Potassium ferricyanide is used in electroplating, laboratory reagent, dyeing wool and in organic chemistry as a mild oxidising agent.

Note: The name of the complex ${{\text{K}}_{\text{3}}}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]$ is potassium ferricyanide. Potassium ferricyanide contains ${\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]^{3 - }}$ ion. The ${\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_{\text{6}}}} \right]^{3 - }}$ ion is an octahedrally coordinated ion because it contains six cyanide ions. Potassium ferricyanide is bright red in colour. It is in the form of crystals or pellets or powder. Potassium ferricyanide is slightly soluble in alcohol and completely soluble in water and acid. The solution of potassium ferricyanide shows yellow-green fluorescence.