A chemical change in which a substance loses oxygen is called reduction. Oxidation and reduction always occur simultaneously.
Basic Knowledge
Reduction is a change in which oxygen is removed from an oxide. A substance that reduces an oxide by taking away its oxygen is called a reducing agent.
Representative reduction reactions:
・Reaction of copper oxide with carbon: 2CuO + C → 2Cu + CO2
CuO is reduced to Cu (it loses oxygen)
C is oxidized to CO2 (it gains oxygen)
・Reaction of copper oxide with hydrogen: CuO + H2 → Cu + H2O
CuO is reduced to Cu
H2 is oxidized to H2O
Oxidation and reduction always occur simultaneously. If one substance is oxidized, another substance is reduced. This is called a redox reaction.
According to this rule, an oxidizing agent (a substance that oxidizes another substance) is itself reduced, while a reducing agent (a substance that reduces another substance) is itself oxidized.
Reduction（a chemical change in which a substance loses oxygen）
Reducing agent（a substance that takes oxygen from another substance. It is itself oxidized）
Oxidizing agent（a substance that gives oxygen to another substance. It is itself reduced）
Redox reaction（a reaction in which oxidation and reduction occur simultaneously）
Smelting（the industrial reduction used to extract iron from iron ore. Coke is used）
Carbon monoxide（CO. Acts as a reducing agent in a blast furnace. It can have stronger reducing power than CO2）
Further Study
The simultaneous occurrence of oxidation and reduction can be clearly seen in iron smelting. In a blast furnace, coke (carbon) burns to produce carbon monoxide (CO), which removes oxygen from iron ore (mainly Fe2O3) to extract iron.Fe2O3 + 3CO → 2Fe + 3CO2
Here, Fe2O3 is reduced to Fe, while CO is oxidized to CO2. This redox mechanism forms the foundation of the modern steel industry.
Familiar examples of redox:
・Firework powder (a mixture of an oxidizing agent and a reducing agent)
・Fuel cells (convert the oxidation of hydrogen into electrical energy)
・Photosynthesis (CO2 is reduced to organic substances, and H2O is oxidized)
- Reduction = losing oxygen (the opposite of oxidation)
- Oxidation and reduction always occur simultaneously
- A reducing agent is itself oxidized, and an oxidizing agent is itself reduced
2CuO + C → 2Cu + CO2: CuO is reduced and C is oxidizedCuO + H2 → Cu + H2O: CuO is reduced and H2 is oxidized- Smelting = reduction used to extract metals from ores
- Reduction of copper oxide → change from black to reddish-orange (Cu)
Points to Note
① Oxidation gains oxygen, while reduction loses oxygen. Do not reverse them. ② Oxidation and reduction occur simultaneously; only one cannot occur by itself. ③ A reducing agent is itself oxidized (it is oxidized while taking oxygen away). This can be confusing, but it must be memorized. ④ In a smelting experiment, you can observe black copper oxide returning to reddish-orange copper.
Practice
- In the reaction
2CuO + C → 2Cu + CO2, state the substances that are oxidized and reduced, respectively. - Oxidation and reduction occur simultaneously. Explain why using the word “oxygen.”
- Briefly explain, using the term “reduction,” the change by which iron is extracted from iron ore in ironmaking.