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Question: Find the oxidation number of \[Fe\] in \[[Fe{\left( {CN{)_6}} \right]^{4 - }}\] ....

Find the oxidation number of FeFe in [Fe(CN)6]4−[Fe{\left( {CN{)_6}} \right]^{4 - }} .

Explanation

Solution

Oxidation number is the charge on an atom which appears due to formation of bonds with the neighboring atoms or ligands. It is denoted by 00, positive or negative sign.

Complete answer:
Oxidation number is also termed as oxidation state is equal to the total number of electrons which an atom either gains or loses during the formation of a chemical bond with another atom or molecule.
In order to determine the oxidation number of any atom the number of bonds both ionic and covalent is to be determined first. The number of bonds decides the number of electrons shared by the considered atom in its ionic form.
The steps involved in assigning the oxidation number or oxidation state of an atom or ion in a compound:
i) Add up the constant oxidation state of other atoms/molecules/ions that are bonded with the central metal ion
ii) The total oxidation state of a molecule or ion is equal to the total charge on the molecule or ion.
In compounds the more electronegative atoms gain electrons from a less electronegative atom and possess negative oxidation states. The numerical value of the oxidation state is equal to change in the number of electrons.
The elements in the periodic table vary in their oxidation number or state according to the number of valence shell electrons present. The octet rule must be satisfied during the formation of bonds.
The given compound is [Fe(CN)6]4−[Fe{\left( {CN{)_6}} \right]^{4 - }}in which the central metal atom is FeFe. This is a coordination complex compound and is negatively charged. Let x be the oxidation state of the metal atom/ion. The FeFe is attached to six cyanide ligands which carry a unit negative charge. Thus the equation is
O.S. of Fe+6×(charge on cyanide ligand)=−4O.S.{\text{ }}of{\text{ }}Fe + 6 \times (charge{\text{ }}on{\text{ }}cyanide{\text{ }}ligand) = - 4
x+6×(−1)=−4x + 6 \times ( - 1) = - 4
x=+2x = + 2 .
Hence the oxidation state or number of FeFe in [Fe(CN)6]4−[Fe{\left( {CN{)_6}} \right]^{4 - }} is +2 + 2 .

Note: Oxidation number or state may be zero, positive or negative. It has to be an integer and not a fraction number as the number of electrons is always integer. Oxidation number is very useful in determining redox reactions where change of oxidation state takes place.