Question

Treatment of cobalt (II) oxide with oxygen at high temperatures gives ${\mathbf{Co}}_{\mathbf{3}}{\mathbf{O}}_{\mathbf{4}}$. Write a balanced chemical equation for this reaction. What is the oxidation state of cobalt in${\mathbf{Co}}_{\mathbf{3}}{\mathbf{O}}_{\mathbf{4}}$ ?

Short answer

The balanced chemical equation is:

$6\mathrm{CoO}+{\mathrm{O}}_2\to 2{\mathrm{Co}}_3{\mathrm{O}}_4$

The oxidation number of cobalt in ${\mathrm{Co}}_3{\mathrm{O}}_4$is 2.6.

Step-by-step solution

Balanced chemical equation

Balanced chemical equations comprise equations where the count of atoms is equal on both sides of the equation.The law of conservation of mass is the important law to be followed while noting down balanced equations.

Oxidation number

The oxidation number of a particular element is the count of electrons it gained or lost in the chemical bond creation.

Balanced chemical equation of the reaction

The molecular formula of Co(II) oxide will be CoO. Thus the reaction between CoO and O₂ is:

$\mathrm{CoO}+{\mathrm{O}}_2\to {\mathrm{Co}}_3{\mathrm{O}}_4$

This is an unbalanced chemical equation. This can be balanced by placing a coefficient of 6 on the reactant side and a coefficient of 2 on the product side.

The balanced chemical equation is:

$6\mathrm{CoO}+{\mathrm{O}}_2\to 2{\mathrm{Co}}_3{\mathrm{O}}_4$

Calculation of oxidation state

Let the oxidation state of Co be x. As the oxidation state of O is -2, then for${\text{Co}}_{\text{3}}{\text{O}}_{\text{4}}$ it can be written as:

$\begin{array}{rcl}3x-8& =& 0\\ 3x& =& 8\\ x& =& \frac{8}{3}\\ & =& 2.6\\ & & \end{array}$

Hence, the oxidation number of cobalt in ${\mathbf{\text{Co}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}_{\mathbf{\text{4}}}$ is 2.6.