IRON (Fe)
1. Introduction
Iron is an important metallic element that is widely used in our everyday lives. It is used in the construction of buildings, bridges, railway lines, vehicles, machines and many other objects.
Iron is a transition metal with the chemical symbol Fe, derived from its Latin name, Ferrum. It has atomic number 26 and belongs to Group 8 of the periodic table.
Iron is one of the most abundant metals in the Earth's crust and is mainly obtained from its ores through extraction in a blast furnace.
2. Occurrence of Iron
Iron occurs naturally in the Earth's crust, mainly in the form of compounds called iron ores. It is rarely found in the free or uncombined state because it readily reacts with oxygen and other elements.
Some important iron ores include:
(a) Haematite
i. Chemical formula: Fe₂O₃
ii. It is reddish-brown in colour.
iii. It is one of the most important ores used in the extraction of iron.
(b) Magnetite
I. Chemical formula: Fe₃O₄
ii. It is black in colour.
iii. It is naturally magnetic and contains a high percentage of iron.
(c) Siderite
I. Chemical formula: FeCO₃
ii. It is also known as iron carbonate.
iii. It is usually brownish or greyish in appearance.
(d) Limonite
i. Approximate formula: Fe₂O₃·xH₂O
ii. It is a hydrated iron(III) oxide.
iii. It is usually yellowish-brown.
(e) Iron Pyrites
i .Chemical formula: FeS₂
ii. It is also called fool's gold because of its golden appearance.
iii. It is not commonly used for iron extraction because of its high sulphur content.
3. Extraction of Iron
Iron is extracted from its ores, mainly haematite (Fe₂O₃), by heating the ore with coke and limestone in a large industrial furnace called a blast furnace.
The process involves the reduction of iron oxide by carbon monoxide.
(a) Raw Materials Used in the Extraction of Iron
The main raw materials are:
1. Iron ore (Haematite, Fe₂O₃): This is the source of iron.
2. Coke (Carbon, C): It serves as a fuel and helps produce carbon monoxide, which reduces the iron ore.
3. Limestone (Calcium carbonate, CaCO₃): It acts as a flux and helps remove impurities.
4. Hot air: It supplies oxygen for the combustion of coke.
(b) The Blast Furnace
A blast furnace is a tall, steel structure lined internally with heat-resistant bricks. It is used for extracting iron from iron ore.
The raw materials are charged into the furnace through the top, while hot air is blown in through openings called tuyeres, located near the bottom.
Animated illustration showing the extraction of iron from haematite in a blast furnace, including the major chemical reactions and separation of molten iron from slag.
The extraction of iron involves the following stages:
1. Combustion of Coke
Hot air is blown into the furnace through the tuyeres.
At the bottom
Coke burns in oxygen to produce carbon dioxide and heat.
C + O₂ → CO₂
The heat produced raises the temperature inside the furnace.
The carbon dioxide produced reacts with more hot coke to form carbon monoxide.
CO₂ + C → 2CO
Carbon monoxide is the main reducing agent in the blast furnace.
At the middle
2. Decomposition of Limestone
Limestone decomposes under the high temperature in the furnace to form calcium oxide and carbon dioxide.
CaCO₃ → CaO + CO₂
Calcium oxide acts as a flux.
Formation of Slag
The calcium oxide reacts with silica (sand), which is an impurity in the iron ore, to form calcium silicate.
CaO + SiO₂ → CaSiO₃
Calcium silicate is called slag.
At the top
3. Reduction of Iron Ore
Carbon monoxide reacts with haematite and removes oxygen from it, producing iron.
Fe₂O₃ + 3CO → 2Fe + 3CO₂
The iron produced melts as it moves into the hotter lower region of the furnace.
6. Separation of Iron and Slag
Molten iron is denser than slag. Therefore, the molten iron collects at the bottom of the furnace, while the lighter molten slag floats above it.
The two products are removed through separate outlets.
(d) Products of the Blast Furnace
The main products are:
1. Molten pig iron: This is the main product. It contains iron, carbon and other impurities.
2. Slag (calcium silicate): This is a by-product formed when the flux combines with silica impurities.
3. Waste gases: These include carbon monoxide, carbon dioxide and nitrogen, among other gases.
(e) Functions of the Raw Materials
(f) Important Equations in Iron Extraction
1. Combustion of coke:
C + O₂ → CO₂
2. Formation of carbon monoxide:
CO₂ + C → 2CO
3. Reduction of haematite:
Fe₂O₃ + 3CO → 2Fe + 3CO₂
4. Decomposition of limestone:
CaCO₃ → CaO + CO₂
5. Formation of slag:
CaO + SiO₂ → CaSiO₃
(g) Uses of Slag
i. It is used in road construction.
ii. It is used in the manufacture of some cement products.
iii. It is used as a construction material.
Note: The iron obtained directly from the blast furnace is called pig iron. It is further processed to produce cast iron and steel.
Types of Iron
Iron is classified into different forms according to its composition, carbon content and method of preparation.
1. Pig Iron
Pig iron is the crude form of iron obtained directly from the blast furnace.
Characteristics:
i. It contains about 3.5–4.5% carbon, although the composition varies.
ii. It contains impurities such as silicon, sulphur, phosphorus and manganese.
iii. It is hard and brittle.
iv. It is mainly used as a raw material for producing cast iron and steel.
2. Cast Iron
Cast iron is produced by remelting pig iron and adjusting its composition.
Characteristics:
i. Generally contains about 2–4% carbon.
ii. It is hard but brittle.
iii. It has good casting properties.
iv. It is used in making engine blocks, pipes, manhole covers and machine parts.
3. Wrought Iron
Wrought iron is the purest form of iron containing very little carbon.
Characteristics:
I. It contains less than about 0.1% carbon.
ii. It is tough, malleable and ductile.
iii. It can be shaped by hammering.
iv. It is more resistant to corrosion than ordinary carbon steel, but it can still rust.
Uses
include ornamental gates, railings and decorative metalwork.
(d) Steel
Steel is an alloy of iron and carbon, usually containing less than about 2% carbon.
Characteristics:
i. It is generally stronger and tougher than pure iron.
ii. Its properties depend on its carbon content and other alloying elements.
iii. It can be modified by adding elements such as chromium, nickel and manganese.
Uses
Steel is used in construction, vehicles, tools, machinery and household appliances.
Physical Properties of Iron
1. Iron is a silvery-grey metal with a shiny surface when freshly polished.
2. It is a solid at room temperature.
3. It is malleable; therefore, it can be hammered into sheets.
4. It is ductile and can be drawn into wires.
5. It is a good conductor of heat and electricity.
6. It is attracted by magnets and can be magnetised.
7. It has a relatively high melting point of about 1538°C.
8. It has a high density of approximately 7.87 g/cm³.
9. It is strong and hard compared with many common metals.
10. It is sonorous and produces a ringing sound when struck.
Chemical Properties of Iron
Iron is a moderately reactive metal. It reacts with oxygen, water, acids and some non-metals.
(a) Reaction with Oxygen
under suitable conditions, it forms iron oxides.
For example, iron reacts with oxygen to form magnetite:
3Fe + 2O₂ → Fe₃O₄
(b) Reaction with Moist Air (Rusting)
Iron reacts slowly with oxygen and moisture in the atmosphere to form rust.
Rust is a reddish-brown substance consisting mainly of hydrated iron(III) oxide.
General equation:
4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O
Rusting weakens iron objects and gradually damages them.
(c) Reaction with Steam
When hot iron reacts with steam, magnetite and hydrogen gas are produced.
3Fe + 4H₂O(g) → Fe₃O₄ + 4H₂
(d) Reaction with Dilute Acids
Iron reacts with dilute hydrochloric acid to form iron(II) chloride and hydrogen gas.
Fe + 2HCl → FeCl₂ + H₂
It also reacts with dilute sulphuric acid:
Fe + H₂SO₄ → FeSO₄ + H₂
(e) Reaction with Sulphur
When iron combines with sulphur under suitable conditions, iron(II) sulphide is formed.
Fe + S → FeS
(f) Reaction with Chlorine
Iron reacts with chlorine to form iron(III) chloride.
2Fe + 3Cl₂ → 2FeCl₃
(g) Displacement Reaction
Iron is more reactive than copper. Therefore, it displaces copper from copper(II) sulphate solution.
Fe + CuSO₄ → FeSO₄ + Cu
The blue colour of copper(II) sulphate solution gradually changes to pale green as iron(II) sulphate forms, while copper is deposited.
6. Uses of Iron
Iron and its alloys have many important applications.
1. Construction: Steel is used in buildings, bridges, railway tracks and reinforcement bars.
2. Manufacturing: Iron is used in making machines, industrial equipment and tools.
3. Transportation: Iron and steel are used in manufacturing cars, ships, trains and other vehicles.
4. Household equipment: Iron and its alloys are used in making pots, pans, gates, doors and cooking equipment.
5. Agriculture: Iron is used in making hoes, cutlasses, ploughs and other farm implements.
6. Electrical industry: Special iron alloys are used in transformer cores and electromagnets.
7. Pipelines: Cast iron and other iron-based materials are used in water and drainage pipes.
8. Food production: Iron compounds are used in some food fortification products and nutritional supplements.
Prevention of Rusting
Rusting can be prevented or reduced by keeping iron away from air and moisture or by protecting its surface.
Common methods include:
1. Painting: Applying paint prevents direct contact with air and moisture.
2. Oiling and greasing: A layer of oil or grease protects the metal surface.
3. Galvanisation: Coating iron or steel with zinc.
4. Electroplating: Coating iron with another metal such as chromium or tin.
5. Alloying: Adding chromium and other elements to produce stainless steel.
6. Plastic coating: Covering the surface with a protective plastic layer.
8. Summary
Iron is an important transition metal with the symbol Fe and atomic number 26. It occurs naturally in ores such as haematite, magnetite, siderite and limonite. Its common commercial forms include pig iron, cast iron, wrought iron and steel.
Iron is strong, malleable, ductile and magnetic. It reacts with oxygen, moisture, acids and non-metals. Its most common disadvantage is rusting, which can be controlled through protective coatings and alloying.
Objective Questions
1. The chemical symbol for iron is:
A. Ir
B. Fe
C. In
D. F
2. The principal ore used in the extraction of iron is:
A. Bauxite
B. Haematite
C. Galena
D. Cassiterite
3. The chemical formula of magnetite is:
A. Fe₂O₃
B. FeCO₃
C. Fe₃O₄
D. FeS₂
4. The process by which iron reacts with moist air to form rust is called:
A. Reduction
B. Neutralisation
C. Rusting
D. Electrolysis
5. The major component of steel is:
A. Copper
B. Iron
C. Aluminium
D. Zinc
6. Which of the following is a method of preventing rusting?
A. Exposing iron to moisture
B. Galvanisation
C. Adding salt water
D. Heating in air
7. The gas produced when iron reacts with dilute hydrochloric acid is:
A. Oxygen
B. Nitrogen
C. Hydrogen
D. Chlorine
8. Iron displaces copper from copper(II) sulphate because iron is:
A. Less reactive than copper
B. More reactive than copper
C. A non-metal
D. Chemically inert
Theory Questions
1. (a) What is iron?
(b) State four iron ores and their chemical formulae.
2. (a) State five physical properties of iron.
(b) Give three chemical properties of iron with balanced equations.
3. Explain four methods of preventing rusting.
4. Differentiate between pig iron, cast iron, wrought iron and steel.
5. State five important uses of iron and its alloys.
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