Question

How to calculate oxidation number of Iron in ferric ferrocyanide $\text{F}{{\text{e}}_{4}}{{[\text{Fe(CN}{{\text{)}}_{4}}]}_{3}}$?

Answer 1

Oxidation number or state is an arbitrary number which is present on an element on an element or atom when they are attached in compound.
In a compound various elements are present which can have either positive or negative charge. In any compound, negative charge is present mainly on electronegative atoms while positive charge is present mainly on electropositive atom.

Complete step by step answer:
Given molecule is $\text{F}{{\text{e}}_{4}}{{[\text{Fe(Cn}{{\text{)}}_{6}}]}_{3}}$
Here $\overset{-}{\mathop{\text{C}}}\,\text{N}$ contain $-1$ charge, where $\text{Fe}$ has variable valency, which can show $+2$ and $+3$ oxidation number due to the presence of $s$ and $d$ electron.s
$\text{Fe}$ has electronic configuration of $3{{d}^{6}}4{{s}^{2}}$ , here $2$ electrons in $s-$ orbital while electrons in d orbital is present.
By losing $2$ electrons of $s-$ orbital it can show $+2$ oxidation state while losing $3$ electrons of $s$ &$d$ orbital combinely forms $+2$ oxidation state.
Here first we find the oxidation state of inner $\text{Fe}$.
$\text{F}{{\text{e}}_{4}}{{[\text{Fe(CN}{{\text{)}}_{6}}]}_{3}}\to 4\text{F}{{\text{e}}^{x+}}+3{{[\text{Fe(CN}{{\text{)}}_{6}}]}^{x-}}$
Here 6$\bar{CN}$ provide $6$ negative charge so total $-\text{ve}$ charge chain be $18(-\text{ve})$ which is stabilized by $\text{Fe}$ , out of $18\,(-\text{ve})$ only $6(-\text{ve})$ charge is balanced by inner $\text{Fe}$ so here
$3{{[\text{Fe(CN}{{\text{)}}_{6}}]}^{x-}}\Rightarrow 3x +(-18)=-12$
$x=+2$
Outer $\text{Fe}$ has oxidation number of $y+$ which is equal to $+12$
$4y=12$
$y=+3$
Oxidation state of $\text{Fe}=+2$ in inner complex while oxidation state of $\text{Fe}=+3$ of outer iron

Oxidation state of $\text{Fe}$ is $+2$ and $+3$ .

Note: In the modern periodic table, metals are present either in extreme left of the periodic table or in the middle of the periodic table. The elements which are present in the middle of the periodic table are called D-block elements because the last electrons are entering into the d block of the element. On the basis of partially filled d blocks they are also known as Transition elements. Transition elements are those elements which have partially filled the sub shell either in their ground state or in any of their combined state. On the basis of it, transition elements form various compounds in which variable valency of it is shown.