Question

Find the oxidation state of Co in its oxo-complex species ${\left[ {C{o_2}{O_4}{{\left( {{C_2}{H_4}} \right)}_2}\left( {{H_2}{O_2}} \right)} \right]^{2 - }}.$
a.) 4
b.) 3
c.) 5
d.) 2

Answer 1

Hint: Before dealing with this question we will first define the oxo complex ,oxidation state in oxo-complex species with few examples and then we will find the required value of oxidation number by the following mentioned method.

Complete answer:
A transition metal oxo complex is an oxo ligand containing coordination complex. Formally ${O^{2 - }}$ an oxo ligand may be linked to one or more metal centres, i.e. it may exist as a terminal or (most commonly) as a bridging ligand. Oxo ligands stabilise a metal's high oxidation states.
The total number of electrons that an atom either gains or loses to form a chemical bond with another atom is oxidation number or oxidation state.
The given compound is ${\left[ {C{o_2}{O_4}{{\left( {{C_2}{H_4}} \right)}_2}\left( {{H_2}{O_2}} \right)} \right]^{2 - }}.$
Now first let the oxidation number of the cobalt (Co) be x.
As we know the oxidation state of $\left( {{C_2}{H_4}} \right) = \left( {{H_2}{O_2}} \right) = 0$ and the oxidation state of O = -2
In ${\left[ {C{o_2}{O_4}{{\left( {{C_2}{H_4}} \right)}_2}\left( {{H_2}{O_2}} \right)} \right]^{2 - }}.$ the charge on the compound is -2.
Therefore
$\Rightarrow 2x + 4 \times \left( { - 2} \right) + 2 \times 0 + 0 = - 2 \\\ \Rightarrow 2x - 8 = - 2 \\\ \Rightarrow x = 3 \\\$

Hence the oxidation state of Co is 3 and the correct option is B.

Note: In the first row of transition metals the maximum oxidation number is equal to the number of valence electrons from scandium (+3) up to manganese (+7). It diminishes in the latter elements though. The maximum oxidation number in the second and third rows is the one of ruthenium and osmium (+8). The main objective of an element to form a bond is to complete its octet.