Ores and compounds

Most metals occur as compounds in ores because they have reacted during geological time. Extraction converts the metal compound into the element, usually by reduction or electrolysis.

Above carbon

Potassium, sodium, calcium, magnesium and aluminium are too reactive for carbon reduction. Their compounds are very stable, so molten electrolysis is used despite high energy cost.

Below carbon

Zinc and iron oxides can be reduced by carbon or carbon monoxide. Copper compounds are easier to reduce, and copper, silver or gold may occur native.

Economic reasoning

Extraction choice depends on reactivity, ore grade, energy cost, environmental effects and metal value. Recycling often requires less energy than extraction from ore.

High-value recall and connections

Essential recall: How is aluminium extracted? By electrolysis of molten aluminium oxide dissolved in cryolite. Why can iron be extracted using carbon monoxide? Iron is below carbon in the reactivity series. Why is electrolysis expensive? It requires large amounts of electrical energy. Practical connection: Given a list of metal oxides and series positions, select electrolysis, carbon reduction or simple heating/native recovery and justify each. Examination connection: The extraction rule refers to the metal’s position relative to carbon.

Review questions and suggested answers