In the following reaction, C + O2 ⟶CO2, which one is reducing agent, which one on oxidized?
The Correct Answer and Explanation is:
In the reaction:
C + O₂ ⟶ CO₂
- Reducing agent: Carbon (C)
- Oxidized substance: Carbon (C)
Explanation
In the chemical reaction between carbon and oxygen to form carbon dioxide, we are dealing with a redox (reduction-oxidation) process. To identify the reducing agent and the substance that is oxidized, we must examine the changes in oxidation states of the elements involved.
Carbon starts as a free element in its elemental form, so its oxidation state is zero. In carbon dioxide (CO₂), carbon is bonded to two oxygen atoms. Oxygen is more electronegative and typically has an oxidation state of negative two in compounds. Since there are two oxygen atoms, the total oxidation state contributed by oxygen is negative four. To balance this, carbon must have an oxidation state of positive four in CO₂.
This means carbon’s oxidation state changes from zero to +4, indicating a loss of electrons. Losing electrons is the defining characteristic of oxidation, so carbon is oxidized.
Now let’s consider oxygen. It begins in molecular form (O₂), which has an oxidation state of zero. In CO₂, each oxygen atom has an oxidation state of –2. Therefore, the oxygen atoms gain electrons during the reaction. Gaining electrons is characteristic of reduction, so oxygen is reduced.
The substance that causes another to be reduced is called the reducing agent, and the one that causes oxidation is the oxidizing agent. Since carbon gives up electrons (is oxidized) and causes oxygen to gain electrons (be reduced), carbon is acting as the reducing agent.
To summarize:
- Carbon is oxidized (its oxidation state increases from 0 to +4).
- Oxygen is reduced (its oxidation state decreases from 0 to –2).
- The reducing agent is carbon, because it donates electrons.
- The oxidizing agent is oxygen, because it accepts electrons.
This simple reaction clearly demonstrates the fundamental principles of redox chemistry.
