Question

What is the oxidation number of Fe in ${\text{Fe}}{{\text{C}}_{\text{2}}}{{\text{O}}_{\text{4}}}$ ?

Answer 1

An oxidation number is a number assigned to an element in a chemical combination that represents the number of electrons lost or gained by that particular atom of that element in the given compound. The oxidation number of an atom varies according to the chemical environment surrounding it.
Complete step by step answer:
Following are the rules to be followed while calculating the oxidation number an element in a given compound:
Any free element has an oxidation number of zero.
For monatomic ions, the overall charge on the species is equal to the oxidation number of that atom.
In the case of a neutral compound, the sum of the oxidation numbers of all the atoms is zero.
In the case of polyatomic ions, the sum of the oxidation numbers of all the atoms is equal to the charge on that ion.
The hydrogen atom has an oxidation state of +1. But if it is bonded to a highly electropositive atom has an oxidation state of -1
The oxygen atom has an oxidation state of -2 and in the case of peroxides, it is -1.
All alkali metals exhibit an oxidation state of +1. And all alkaline earth metals have an oxidation state of +2.
Keeping all the above points in mind let us calculate the oxidation number of Fe in ${\text{Fe}}{{\text{C}}_{\text{2}}}{{\text{O}}_{\text{4}}}$.
Here, in the given compound there are two ionic species, one iron ion and second in oxalate anion. Oxalate anion has a charge of -2, which means an oxidation state of -2. Let us assume that iron has an oxidation state of x then we have,
${\text{x - 2}}$ = 0, which gives us x = 2. Thus the oxidation number of Fe in ${\text{Fe}}{{\text{C}}_{\text{2}}}{{\text{O}}_{\text{4}}}$ is 2.

Note: Transition metals (d-block elements) of the periodic table exhibit variable oxidation. This means that they do not have only one oxidation state but their oxidation state varies according to their chemical environment and this is because the last electron in these metals enters in the penultimate shell. Osmium is the element known for having the highest number of oxidation states.