Question

What is the Oxidation state of Cobalt in $ Na[Co(N{H_2})(en)(N{O_2})({S_2}{O_3})] $ ?

Answer 1

Hint: Oxidation number of an element is the no. of electrons that is gained or lost by the atom. The charge written as the superscript is the Oxidation Number of that atom. Some atoms like Oxygen, Nitrate, etc. show fixed oxidation state. The addition and subtraction of the known oxidation state, will give us the oxidation state of the unknown element.

Complete Step By Step Answer:
We are given a Coordination complex $ Na[Co(N{H_2})(en)(N{O_2})({S_2}{O_3})] $ . The overall charge on the complex is Zero, Neutral. The compound outside the coordination sphere in Na which has a fixed oxidation state of +1. Therefore, the coordination sphere should have a charge of -1 for the whole complex to be neutral.
The coordination compound has a central metal atom that is linked to various ligands. The ligands are the donor atoms that donate electrons or lone pairs to the central metal atom. Ligands are attached to the central atom by coordinate bonds. There are primarily three types of ligands:
a. Positive ligands (which have a positive charge)
b. Negative ligands (which have a negative charge)
c. Neutral ligands (which has zero or no charge)
The overall charge of the complex is zero. Hence we’ll add up all the oxidation states of the ligands and find the unknown O.S of Cobalt.
The oxidation state of Na atoms is always found to be $ + 1 $ always.
The oxidation state of $ N{H_2} $ is $ - 1 $ . It is an anionic ligand.
The oxidation state of $ (ethylenediamine) $ is neutral i.e., 0
Oxidation state of $ N{O_2} $ is $ - 1 $ and that of $ {S_2}{O_3} $ is $ - 2 $
Consider the charge on cobalt to be ‘x’. Therefore, the overall charge can be given as: $ x + ( - 1) + 0 + ( - 1) + ( - 2) = - 1 $
 $ x - 4 = - 1 \to x = - 1 + 4 = + 3 $
Therefore, the oxidation state of Co is +3.

Note:
If we are told to find the oxidation state of the central atom in the complex, the oxidation state of the ligands are considered together itself. The oxidation state of individual atoms is not considered. The overall charge of the complex is equal to the sum of the oxidation states of the central atom and the ligands.