38. Extraction of Metals & Reduction

1. Key Definitions

• Oxidation: The process of gaining oxygen (e.g., Magnesium + Oxygen → Magnesium Oxide).

• Reduction: The process of losing oxygen (e.g., Magnesium Oxide → Magnesium + Oxygen).

• Metal Ore: A rock that contains enough metal-rich compounds to make it worthwhile to extract the metal from.

• Native Metals: Very unreactive metals, like gold, that are found in the earth as pure metals because they do not react with oxygen.

2. The Role of Oxygen

Most metals are reactive enough to react with oxygen in the atmosphere to form metal oxides.

• Iron naturally reacts with oxygen to form iron oxide, commonly known as rust.

• To obtain pure metal from these oxides, the oxygen must be removed via reduction.

3. Extraction Using Carbon

The cheapest way to extract a metal from its oxide is to react it with carbon.

• The Process: Carbon "steals" the oxygen from the metal oxide to form carbon dioxide, leaving behind the pure metal.

• Example: Copper Oxide + Carbon → Copper + Carbon Dioxide.

  • The Copper is reduced (loses oxygen).

  • The Carbon is oxidized (gains oxygen).

4. The Reactivity Series Rule

Extraction with carbon only works for metals that are less reactive than carbon.

• Metals below Carbon: Zinc, Iron, and Copper can be extracted by reduction with carbon.

• Metals above Carbon: Potassium, Sodium, Lithium, Calcium, Magnesium, and Aluminium are too reactive for carbon to remove their oxygen.

• Electrolysis: Metals more reactive than carbon must be extracted using electrolysis, which requires a large amount of energy and is much more expensive.

5. Case Study: Iron Extraction

• Iron is commonly found in the ore Hematite (Fe₂O₃).

• Since iron is less reactive than carbon, it can be extracted using carbon and heat.

• Equation: 2Fe₂O₃ + 3C → 4Fe + 3CO₂