Question
When a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed when the oxidising agent is in excess. Justify this statement giving three illustrations.
Solution
The Fact given in the question is clear from the following illustration.
First illustration: Carbon is a reducing agent while oxygen is an oxidising agent; Let carbon be taken in excess and allowed to burn in a limited supply of O2. CO has formed in which carbon has +2 oxidation state (lower oxidation state).
Also, let O2 be taken in excess, then initially formed CO gets oxidised to CO2 in which carbon has +4 oxidation state (higher oxidation state).
Second illustration. Sodium is a reducing agent while oxygen is an oxidising agent. Let sodium be taken in excess and allowed to burn in a limited supply of O2. Sodium oxide (Na2O) is formed in which oxygen has -2 oxidation state.
On the other hand, let O2 be taken in excess, then Na2O2 is formed in which has -1 oxidation state which is higher than -2.
Third illustration P4 is a reducing agent while Cl2 is an oxidising agent. Let P4 be taken in excess and allow to react it with Cl2, then PCl3 is formed in which P has +3 oxidation state.
On the other hand, let Cl2 be taken in excess, then initially formed PCl3 reacts further to form PCl5 in which P has +5 oxidation state.
First illustration: Carbon is a reducing agent while oxygen is an oxidising agent; Let carbon be taken in excess and allowed to burn in a limited supply of O2. CO has formed in which carbon has +2 oxidation state (lower oxidation state).
Also, let O2 be taken in excess, then initially formed CO gets oxidised to CO2 in which carbon has +4 oxidation state (higher oxidation state).
Second illustration. Sodium is a reducing agent while oxygen is an oxidising agent. Let sodium be taken in excess and allowed to burn in a limited supply of O2. Sodium oxide (Na2O) is formed in which oxygen has -2 oxidation state.
On the other hand, let O2 be taken in excess, then Na2O2 is formed in which has -1 oxidation state which is higher than -2.
Third illustration P4 is a reducing agent while Cl2 is an oxidising agent. Let P4 be taken in excess and allow to react it with Cl2, then PCl3 is formed in which P has +3 oxidation state.
On the other hand, let Cl2 be taken in excess, then initially formed PCl3 reacts further to form PCl5 in which P has +5 oxidation state.
