Question

Name the oxidised, reduced, oxidising agents and reducing agents in the following equations and complete the equation as well. ${\text{Ca}} + {{\text{O}}_2} \to$

Answer 1

To solve this we must first write the complete balanced reaction. Then calculate the oxidation state of all the species. If the oxidation state of the species increases then it is getting oxidised and if the oxidation state decreases it is getting reduced.

Complete step-by-step solution :
We are given a reaction,
${\text{Ca}} + {{\text{O}}_2} \to$
Calcium metal reacts with oxygen to form calcium oxide. The complete reaction is as follows:
${\text{2Ca}} + {{\text{O}}_2} \to 2{\text{CaO}}$
Thus, the complete equation is ${\text{2Ca}} + {{\text{O}}_2} \to 2{\text{CaO}}$.
In the reaction, we will calculate the oxidation state of each species.
We know that the oxidation state of an element in its free or uncombined state is always zero.
Thus, the oxidation state of ${\text{Ca}}$ is zero and the oxidation state of ${{\text{O}}_2}$ is also zero.

Now let us calculate the oxidation state of calcium in ${\text{CaO}}$.
We know that the oxidation state of oxygen is -2. The total charge on the compound ${\text{CaO}}$ is zero. Thus,
Oxidation state of calcium $= {\text{Total charge on compound}} - {\text{Oxidation state of O}}$
Oxidation state of calcium $= 0 - \left( { - 2} \right)$
Oxidation state of calcium $= + 2$

The oxidation state of calcium in the given reaction changes from 0 to $+ 2$. Thus, the oxidation state of calcium increases. Thus, as the oxidation state of calcium increases, we can say that calcium is getting oxidised.

We know that the chemical species in the chemical reaction which itself gets oxidised and reduces the other species is known as a reducing agent. Thus, calcium is a reducing agent.The oxidation state of oxygen in the given reaction changes from 0 to $- 2$. Thus, the oxidation state of oxygen decreases. Thus, as the oxidation state of oxygen decreases, we can say that oxygen is getting reduced.

We know that the chemical species in the chemical reaction which itself gets reduced and oxidised the other species is known as an oxidising agent. Thus, oxygen is an oxidising agent
Thus, calcium gets oxidised, oxygen gets reduced, oxygen is an oxidising agent and calcium is a reducing agent.

Note: If the oxidation state increases, the species gets oxidised. As the species gets oxidised we can say that it is a reducing agent. If the oxidation state decreases, the species gets reduced. As the species gets reduced we can say that it is an oxidising agent.