Metals in the Earth's crust
- Almost all metals are found in the Earth's crust combined with other elements as
- An ore is a rock that contains enough of a wanted metal compound to make extraction economically worthwhile
- Many metal ores are metal oxides; some are sulfides or carbonates
- Iron is found mainly as , an iron(III) oxide (Fe2O3)
- Aluminium is found mainly as , a hydrated aluminium oxide ore that is purified to give Al2O3 before extraction
- Copper is found as the sulfide ore chalcopyrite (CuFeS2) and as carbonate ores such as malachite
Native metals
- A few very unreactive metals are found as the free element in the Earth's crust, not as compounds
- These include gold, platinum and (to a lesser extent) silver
- They occur uncombined because they react so slowly with air, water and acids that they survive in their pure form on geological timescales
Extraction is a reduction
- For an oxide ore, extracting the metal means removing oxygen from the metal compound — by definition, a reaction
- The reactivity series decides how that reduction is carried out (see section 2)
Stating why extracting a metal from its oxide counts as reduction
What comes up: a 1-mark question asking you to explain why converting a metal oxide into the metal is called a reduction.
Write: the metal oxide loses oxygen (in the reaction).
Watch out: the mark scheme ignores "the metal oxide gains electrons" — that answer scores zero. Stick with the oxygen definition here.