Metallurgy
ICSE Class 10 · Chemistry · Chapter 7
What this chapter covers
- Occurrence of metals in nature
- Stages in the extraction of metals
- Concentration of the ore: pulverisation and dressing
- Conversion of the ore to oxide: roasting and calcination
- Reduction of metallic oxides
- Electro-refining of metals
- Extraction of aluminium: purification of bauxite by Baeyer's process
- Extraction of aluminium: electrolysis by the Hall-Héroult process
- Alloys and amalgams
Key definitions
Metallurgy is the branch of chemistry that deals with the extraction of metals from their ores and the refining of the extracted metals for use.
A mineral is a naturally occurring substance, element or compound, found in the Earth's crust, that has a definite chemical composition.
An ore is a mineral from which a metal can be extracted conveniently and profitably.
Gangue is the unwanted earthy and rocky material, such as sand, clay and silica, that is mixed with an ore when it is mined.
Pulverisation is the process of crushing large lumps of ore in jaw crushers and then grinding them to a fine powder in ball mills or stamp mills.
Hydraulic washing is the method of concentrating an ore by washing the powdered ore in a stream of running water, so that the lighter gangue particles are carried away and the heavier ore particles settle down.
Magnetic separation is the method of concentrating an ore in which either the ore or the gangue is magnetic, so that the two can be separated by a magnet.
Froth flotation is the method of concentrating sulphide ores in which the powdered ore is mixed with water and an oil, and air is blown through, so that the ore particles are carried to the surface in the froth while the gangue sinks.
Roasting is the process of heating a concentrated ore, usually a sulphide ore, strongly in a free supply of air, below its melting point, so that it is converted into its oxide.
Calcination is the process of heating a concentrated ore strongly in the absence of air or in a limited supply of air, below its melting point, so that it loses carbon dioxide, water or other volatile matter and is converted into its oxide.
Reduction of a metallic oxide is the removal of oxygen from the oxide to leave the free metal.
Electro-refining is the purification of an impure metal by electrolysis, using the impure metal as the anode, a thin sheet of the pure metal as the cathode, and a solution of a soluble salt of the same metal as the electrolyte.
Key points
- Metallurgy is the extraction of metals from their ores and their refining; most metals occur combined, only unreactive ones occur native.
- A mineral is a naturally occurring compound of definite composition; an ore is a mineral from which the metal is extracted profitably. All ores are minerals, but not all minerals are ores.
- Ores of iron: haematite Fe2O3, magnetite Fe3O4, siderite FeCO3; of aluminium: bauxite Al2O3 · 2H2O, cryolite, corundum; of zinc: zinc blende ZnS, calamine ZnCO3, zincite.
- Extraction has three stages: concentration, conversion to oxide, and reduction (with refining where needed).
- After pulverisation, ores are concentrated by hydraulic washing (density), magnetic separation (magnetism) or froth flotation (wetting by oil, for sulphide ores).
- Roasting heats sulphide ores in excess air and gives SO2; calcination heats carbonate and hydrated ores in the absence or limited supply of air and gives CO2 or water.
- Oxides of Cu, Pb, Fe and Zn are reduced by carbon or carbon monoxide; CuO, PbO and Fe2O3 also by hydrogen. Al2O3 and MgO are not reduced this way.
- Na, K and Ca are obtained by electrolysis of their fused chlorides; the metal ion gains electrons at the cathode.
- Electro-refining uses impure metal as anode, pure metal as cathode and a salt of the metal as electrolyte; precious metals collect as anode mud.
- Baeyer's process: bauxite + NaOH gives sodium aluminate; red mud is filtered off; dilution and seeding precipitate Al(OH)3; ignition gives pure Al2O3.
- Hall-Héroult process: alumina in molten cryolite and fluorspar at about 950 °C; graphite lining cathode, graphite rod anodes; Al3+ + 3e- → Al at the cathode, oxygen at the anode, which burns the anodes away.
- Alloys are harder, stronger or more corrosion-resistant than pure metals: stainless steel (Fe, Cr, Ni), magnalium (Al, Mg), duralumin (Al, Cu, Mg, Mn), brass (Cu, Zn), bronze (Cu, Sn), solder (Pb, Sn). An amalgam is an alloy containing mercury.
Questions answered
Define a mineral and an ore. Why is every ore a mineral but not every mineral an ore?
Name one ore each of iron, aluminium and zinc, with formulae.
What is gangue? Why must it be removed before the ore is reduced?
Which method of concentration is used for (a) galena, (b) haematite, (c) magnetite? State the property on which each depends.
In froth flotation, what is the role of (a) pine oil, (b) air?
Distinguish between roasting and calcination, with one equation for each.
Write equations for the reduction of (a) iron(III) oxide by carbon monoxide, (b) lead(II) oxide by carbon, (c) copper(II) oxide by hydrogen.
Why are sodium and calcium extracted by electrolysis of their fused chlorides and not of their aqueous solutions?
Past board exam questions
ICSE 2027 sample paper · 1 mark
The set-up described below shows that P reacts with dilute hydrochloric acid to produce a gas which when passed through substance Q, reduces it. In the set-up, P lies in dilute hydrochloric acid in a conical flask fitted with a thistle funnel; the gas evolved passes through a delivery tube into a horizontal tube where substance Q is heated. What are substances P and Q?
- P - copper, Q - lead (II) oxide
- P - lead, Q - magnesium oxide
- P - magnesium, Q - calcium oxide
- P - zinc, Q - copper (II) oxide
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ICSE 2027 sample paper · 3 marks
Name the following: (a) The non-metallic element which is used as the anode during electrolytic reduction of fused alumina in Hall Heroult’s process. (b) An alloy which is made up of aluminium and magnesium only. (c) The process of heating the concentrated ore in a limited supply of air or in the absence of air.
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ICSE 2026 board paper · 1 mark
In the electrolysis of molten aluminium oxide for extraction of aluminium, the following reactions take place: 1. Al³⁺ + 3e⁻ ⟶ Al 2. 2O²⁻ ⟶ O₂ + 4e⁻ 3. C + O₂ ⟶ CO₂ 4. Al₂O₃ ⇌ 2Al³⁺ + 3O²⁻ The reaction that takes place at the negative electrode is:
- 1
- 2
- 3
- 4
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ICSE 2026 sample paper · 2 marks
Name the main metal present in the following alloys: (a) Duralumin (b) Brass
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ICSE 2026 sample paper · 2 marks
The following questions relate to the extraction of Aluminium by electrolysis. (a) Name the other compound which contains aluminium added to alumina. (b) Give a balanced equation for the reaction that takes place at the cathode.
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ICSE 2026 board paper · 2 marks
Bauxite is the principal ore used in the commercial extraction of aluminium. The Bayer's process is used to refine bauxite into pure alumina, with caustic soda playing a crucial role in the initial stage of the process. Based on this, answer the following questions: (a) Explain the reason behind the addition of caustic soda during the Bayer's process. (b) Write a balanced chemical equation representing the reaction between bauxite and caustic soda during the Bayer's process.
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ICSE 2025 compartment paper · 1 mark
Read the statements given below: I – Copper is a component in the alloy that is used to make medals. II – Aluminium is used in making the alloy stainless steel. III – Copper is a common component of both duralumin and brass. Which of the statements are correct?
- I & II
- I & III
- II & III
- I, II & III
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ICSE 2025 board paper · 1 mark
The metal whose oxide can be reduced by common reducing agents:
- Copper
- Sodium
- Aluminium
- Potassium