Grade 8: Iron Extraction and Reduction

• Grade 8 Final revision sheet for 2024-2025

Iron Extraction and Reduction

• At high temperatures, iron(III) oxide (Fe2O3) is reduced by carbon.
• The equation for the reaction is: Fe2O3 + 3C → 2Fe + 3CO
• Iron(III) oxide loses oxygen and becomes iron (Fe) while carbon gains oxygen and becomes carbon dioxide (CO2)
• Iron is extracted from haematite by mixing the ore with limestone and coke in a blast furnace.
• In the furnace, iron ore is reduced to iron, and impurities react with calcium oxide to form slag
• The main ore that contains Fe2O3 in iron is hematite.
• The iron in Fe2O3 is reduced by reaction with carbon monoxide, shown in the balanced equation: Fe2O3 + 3CO → 3CO2 + 2Fe
• The oxidation number of iron is reduced from +3 to 0.
• The oxidation number decreases from +3 to 0 indicates the iron has been reduced.
• The major impurity in iron ore is silicon (IV) oxide and removed by adding limestone in the blast furnace
• The equation for this is: CaCO3 -> CaO + CO2 (Thermal Decomposition) and CaO + SiO2 -> CaSiO3 (Neutralization).

Manufacturing Iron in a Blast Furnace

• Three starting materials in a blast furnace include coke, iron ore and limestone
• Another starting material added to the blast furnace is air/oxygen

Limestone and Lime

• One use of limestone is making cement
• Coke is mainly carbon and its burning equation is C + O2 → CO2
• Combustion/ is an exothermic reaction
• Thermal decomposition of limestone (calcium carbonate) results in Calcium oxide + Carbon dioxide.

Metals and Extraction Methods

• 2 metals extracted by electrolysis: Aluminum and Magnesium
• 2 metals extracted by reduction with C/CO: Iron and Zinc

Rusting and Corrosion

• Corrosion is the gradual damage of a metal due to its reaction with oxygen in the air, other nonmetals, changing to weak ionic compounds.
• Rusting is the reaction in which iron (Fe) reacts with oxygen (O2) and water (H2O) to form hydrated iron(III) oxide (Fe2O3·xH2O).
• Two main factors required for rusting are oxygen and water.
• Three ways to prevent rusting are galvanizing, greasing and painting.

Aluminum Extraction by Electrolysis

• Aluminum is extracted from aluminum oxide by electrolysis.
• Products for electrolysis are CO2 and O2.
• At the cathode: Al3+ + 3e- → Al
• At the anode: 2O2- → O2 + 4e-
• Aluminum oxide is dissolved in molten cryolite to lower the melting temperature and increase the conductivity
• Carbon anodes require regular replacement due to burning with produced oxygen at high temperatures

Blast Furnace Reactions

• Carbon monoxide forms high in the blast furnace due to insufficient (limited) oxygen.
• The equation for the reduction of hematite with carbon monoxide: Fe2O3 + 3CO → 2Fe + 3CO2
• When limestone decomposes, carbon dioxide is produced.
• The equation for calcium oxide reacting with silicon(IV) oxide: CaO + SiO2 → SiO3.
• Layers separate because slag is immiscible with molten iron and less dense.
• The molten iron doesn't react with air because a layer of slag prevents hot iron from reacting with oxygen, and/or all oxygen reacts with carbon.

Rust Prevention

• The two substances causing iron to rust are oxygen and water.
• Aluminum oxide (Al2O3) layer is non-porous and adheres strongly to the metal surface which prevents further oxygen and water from reaching the underlying aluminum: stopping further corrosion
• Rust is porous which allows oxygen and water to pass through and contact the underlying layers: This continuous exposure to O2 and H2O leads to further oxidation and ongoina corrosion of iron.
• In sacrificial protection, zinc is more reactive than iron and oxidizes in preference to iron.

Alloys

• An alloy is a homogenous mixture of a metal with other elements, such as carbon.
• Alloys are more useful than pure metals because they are stronger and harder.
• Magnesium and aluminum alloys are resistant to corrosion.

Rock Types

• The three main types of rocks are Igneous, Sedimentary, and Metamorphic.
• Igneous rocks form from cooled magma or lava.
• Metamorphic rocks form due to heat and pressure.
• Sedimentary rocks form by accumulation of sediments.

Igneous Rocks

• Basalt is an example of an igneous rock
• Intrusive rocks cool inside Earth; extrusive rocks cool on the surface

Metamorphic Rocks

• Slate is a metamorphic rock

Fossils

• Sedimentary rock is most likely to contain fossils

Rock Formation

• Sedimentary rock turns into metamorphic rock through heat and pressure.
• Sedimentary rocks form through compaction and cementation.

Conditions for Rusting

• The two substances essential for iron to rust are oxygen and water.
• The chemical name for rust is iron(III) oxide.
• Coating the iron with zinc is commonly used to prevent iron from rusting.
• Painting an iron surface prevents rusting as it provides a barrier against oxygen and water.