Question

What is the oxidation number of carbon in ${\text{C}}{{\text{O}}_2}$?

Answer 1

Hint- Here, we will proceed by defining the term oxidation number or oxidation state. Then, we will see the relation between oxidation number and charge. Then, we will apply the concept that the total charge on any neutral compound is always zero.

Complete answer:
Oxidation number is also called Oxidation State which is defined as the total number of electrons which an atom either gains or loses to form a chemical bond with another atom.
By definition, an atom's oxidation number is the charge an atom would get if the compound were made up of ions.
As we know that oxygen generally exists in a state having charge of -2
Charge on oxygen atom = -2
Also, we know that the total charge on any neutral compound is always zero and the total charge on any neutral compound will be equal to the sum of the charges on the substituent atoms.
Since, the total charge on any neutral compound ${{\text{A}}_x}{{\text{B}}_y}{{\text{C}}_z}$ is given by
Total charge on the atom ${{\text{A}}_x}{{\text{B}}_y}{{\text{C}}_z}$ = x(Charge on atom A) + y(Charge on atom B) + z(Charge on atom C)
But total charge on the neutral atom ${{\text{A}}_x}{{\text{B}}_y}{{\text{C}}_z}$ is zero, we have
x(Charge on atom A) + y(Charge on atom B) + z(Charge on atom C) = 0
Using the above concept for the neutral compound ${\text{C}}{{\text{O}}_2}$, we get
$ \Rightarrow $ 1(Charge on C atom) + 2(Charge on O atom) = 0
$ \Rightarrow $ Charge on C atom = -2(Charge on O atom)
By substituting Charge on O atom = -2 in the above equation, we get
$ \Rightarrow $ Charge on C atom = -2(-2) = 4

So, the oxidation number of carbon in carbon dioxide (${\text{C}}{{\text{O}}_2}$) is +4.

Note- The oxidation number of an atom in a neutral material containing atoms of only one element is zero. The atoms in ${{\text{O}}_2}$, ${{\text{O}}_3}$, ${{\text{P}}_4}$ and ${{\text{S}}_8}$, all of them have an oxidation number of 0. The number of simple ions oxidizing is equal to the charge on the ion. In a neutral compound the sum of the oxidation numbers is zero.