Question

What is the oxidation state of ${\left[ {Fe{{\left( {{H_2}O} \right)}_5}NO} \right]^{2 + }}$
A. 1
B. 2
C. 3
D. None of these

Answer 1

To answer this question, you should recall the concept of oxidation numbers. The oxidation state of an atom is defined as the number of electrons lost and, therefore, describes the extent of oxidation of the atom. For example, the oxidation state of carbon in ${\text{C}}{{\text{O}}_{\text{2}}}$ would be $+ 4$ since the hypothetical charge held by the carbon atom if both of the carbon-oxygen double bonds were completely ionic would be equal to $+ 4$.

Complete step by step answer:
- The most frequent terms Oxidation state and oxidation number are terms frequently used interchangeably. They are defined and described as the number of electrons lost in an atom. The values can be zero, positive, or negative.
- Coordination compounds are defined as the compounds containing an array of anions or neutral molecules that are bound to a central atom through coordinate covalent bonds. A chemical compound in which the central ion or atom is connected to atoms, molecules, or ions is called a coordination entity. The central atoms or ion is the one to which atoms, molecules, or ions are bound.
- The oxidation number is characterized as the charge that the atom on the centre conveys as determined by considering proper charges to the ligands and then comparing the total of the charges on the central atom and ligands equivalent to the charge on the coordination sphere.
- Let the oxidation state of Fe be ${\text{x}}$. There is the presence of 5 water ligands which are neutral.
The nitrosyl ligand is also a neutral ligand and carries a charge of 0.
The sulphate ion shows a stable charge of $- 2$ but as the molecule in whole is a neutral the coordination sphere ${\left[ {Fe{{\left( {{H_2}O} \right)}_5}NO} \right]^{2 + }}$ must carry a charge of +2.
So, by adding all the oxidation states and equating with the total oxidation state of the complex:
$x + 5\left( 0 \right) + 1\left( 0 \right) = + 2$
$\Rightarrow x = + 2$
So, the oxidation state of Fe is +2.

Hence, the correct option is option B.

Note:
In most of the compounds, the oxidation number of oxygen is $- 2$. There are two exceptions here.
Peroxides: Each oxygen atom exhibits an oxidation number of $- 1$. Example, $N{a_2}{O_2}$
Superoxide- Every oxygen atom is allocated an oxidation number of $- \dfrac{{{\text{ }}1}}{2}$. Example, $K{O_2}$
Oxygen is bonded to fluorine- Example, dioxygen difluoride where the oxygen atom is allocated an oxidation number of $+ 1$.