10 min readPathway sheetSection A MCQ (1 mark) and true or false (2 marks, two parts); Section B short answer (3 marks) on roasting, calcination or the thermite process

Minerals, ores and the extraction of metals

An ore is a mineral from which a metal can be extracted profitably. How we extract a metal depends on its place in the reactivity series.

MineralA naturally occurring substance in the earth's crust that contains a metal or its compounds

OreA mineral with a high percentage of a metal, from which the metal can be extracted profitably. Every ore is a mineral, but not every mineral is an ore

MetallurgyThe steps for getting a pure metal from its ore

Roasting and calcinationRoasting: heating a sulphide ore strongly in air. Calcination: heating a carbonate ore strongly with little or no air

Steps in getting a metal

Very reactive metals skip the oxide step: their molten compounds are electrolysed.

Extraction depends on reactivity

Group	Metals	How the metal is obtained	Example
Low reactivity	Hg, Cu; Ag and Au are often found free	Heating the ore in air is enough	Mercury from cinnabar, HgS: 2HgS + 3O₂ → 2HgO + 2SO₂, then 2HgO → 2Hg + O₂
Medium reactivity	Zn, Fe, Pb	Turn the sulphide or carbonate ore into the oxide, then reduce it with carbon	ZnO + C → Zn + CO
High reactivity	K, Na, Ca, Mg, Al	Electrolysis of the molten compound, because carbon cannot reduce their oxides	Sodium from molten NaCl; aluminium from Al₂O₃

Roasting and calcination

RoastingA sulphide ore is heated strongly in air. It gives the oxide and sulphur dioxide: 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g).

CalcinationA carbonate ore is heated strongly with little or no air. It gives the oxide and carbon dioxide: ZnCO₃(s) → ZnO(s) + CO₂(g).

Metals are easier to get from oxides, so both steps come before reduction. Getting a metal from its compound is always a reduction: the removal of oxygen.

Reduction by aluminium: the thermite process

A very reactive metal can take oxygen from the oxide of a less reactive metal. This is a displacement reaction.
Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + heat.
So much heat is given out that the iron forms as a liquid.
It is used to weld railway tracks and to repair cracked heavy machine parts.

Electrolysis of molten sodium chloride

1
Melt sodium chloride so that its ions can move: NaCl → Na⁺ + Cl⁻.
2★
At the cathode (negative electrode): Na⁺ + e⁻ → Na
Sodium metal forms
3
At the anode (positive electrode): 2Cl⁻ → Cl₂ + 2e⁻
Chlorine gas is given off
4
Aluminium is made in a similar way, by electrolysis of its oxide, Al₂O₃.

★ key step

In real life

Indian Railways joins rail tracks on site with the thermite process, pouring white-hot liquid iron into the gap. The aluminium of your pressure cooker was made by electrolysis, because carbon cannot take oxygen away from aluminium.

Exam angle

2 marks: “Define (i) an ore and (ii) metallurgy.” (i) An ore is a mineral from which a metal can be extracted profitably. (ii) Metallurgy is the set of steps for getting a pure metal from its ore.

3 marks: “Why can mercury be obtained just by heating its ore in air, while zinc needs carbon? Write one equation for each.” Mercury is low in the reactivity series, so heat alone is enough: 2HgS + 3O₂ → 2HgO + 2SO₂, then 2HgO → 2Hg + O₂. Zinc is in the middle, so its oxide must be reduced with carbon: ZnO + C → Zn + CO.

1 marks: “Which process gives sodium metal from sodium chloride?” Electrolysis of molten sodium chloride.

Remember it

Low: just heat. Middle: oxide, then carbon. Top: electricity. Sulphide is roasted, carbonate is calcined.