Extraction Of Metals

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Notes

Metals and Ores

The Earth’s crust contains metals and metal compounds.
A **metal ore** is a rock containing enough metal to make extraction worthwhile.
Many metal ores are **oxides** (e.g., hematite – iron ore, bauxite – aluminium ore).
Extraction involves **removing oxygen** from the compound, so it is a **reduction** process.
Very unreactive metals like **gold** and **platinum** occur **native** (uncombined).

Reactivity Series and Extraction Method

The **higher** a metal in the reactivity series, the **harder** it is to extract.
Metals **above carbon** must be extracted by **electrolysis** (e.g., aluminium).
Metals **below carbon** can be extracted by heating with **carbon** or **carbon monoxide** (e.g., iron in blast furnace).
Very unreactive metals (e.g., gold, silver) are often found **native** or require little processing.

Extraction of Iron from Hematite – The Blast Furnace

Iron is extracted in a **blast furnace** from its ore **hematite** (Fe₂O₃).
Raw materials: **iron ore**, **coke** (impure carbon), and **limestone** are added at the top.
**Hot air** is blown into the bottom.
**Zone 1:** Coke burns in hot air to form CO₂, providing heat: C + O₂ → CO₂.
**Zone 2:** Coke reacts with CO₂ to form **CO** (main reducing agent): C + CO₂ → 2CO.
**Zone 3:** CO reduces iron(III) oxide to molten iron: Fe₂O₃ + 3CO → 2Fe + 3CO₂.
**Limestone** decomposes to CaO, which reacts with SiO₂ impurity to form **slag** (calcium silicate).
Molten iron and slag are **tapped off** separately.

Extraction of Aluminium from Bauxite – Electrolysis

Aluminium is **above carbon** in the reactivity series, so it cannot be reduced by carbon.
Its ore is **bauxite** (aluminium oxide, Al₂O₃).
Aluminium oxide is **dissolved in molten cryolite** to lower the melting point.
The mixture is **electrolysed** using carbon electrodes.
**Aluminium ions** are reduced at the **cathode** to form molten aluminium metal.
**Oxide ions** are oxidised at the **anode** to form oxygen gas.
The carbon anodes are **burned away** by the oxygen and must be replaced regularly.

Key Equations (Extended Tier)

Burning of coke: C(s) + O₂(g) → CO₂(g)
Formation of CO: CO₂(g) + C(s) → 2CO(g)
Reduction of iron ore: Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)
Thermal decomposition of limestone: CaCO₃(s) → CaO(s) + CO₂(g)
Slag formation: CaO(s) + SiO₂(s) → CaSiO₃(l)

Atomic structure of iron (Fe).

Practice questions

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1.What is a metal ore?
Easy
- AA rock that contains enough of a metal to make extraction worthwhile
- BA pure metal found in the Earth's crust
- CA compound of a metal with oxygen only
- DA mineral that contains carbon
2.Extraction of a metal from its ore is a reduction process because oxygen is removed from the compound.
Easy
True or false?
3.Which metal is found native (uncombined) in the Earth's crust?
Easy
- AIron
- BAluminium
- CGold
- DZinc
4.Complete the sentence about the extraction of iron.
Medium
In the blast furnace, the main reducing agent $is ____$ .
5.State two raw materials added to the top of the blast furnace for iron extraction.
Medium
6.How many tonnes of iron does a modern blast furnace produce per day?
Medium
- A9000
- B10000
- C12000
- D11000
7.Why is aluminium extracted by electrolysis rather than by heating with carbon?
Medium
- AAluminium is more reactive than carbon
- BAluminium is less reactive than carbon
- CAluminium ore is not an oxide
- DAluminium has a low melting point
8.What is the purpose of adding limestone to the blast furnace?
Medium

Slides

Metals and Ores

The Earth’s crust contains metals and metal compounds.
Useful metals are often chemically combined with other substances in rocks called ores.
A metal ore is a rock that contains enough of the metal to make it worthwhile extracting.

What is a metal ore?

A pure metal found in the Earth's crust
A rock containing enough metal to make extraction worthwhile
A compound of a metal with oxygen
A mixture of metals

Why Extraction is a Reduction Process

Many metal ores are oxides.
Extracting the metal involves removing oxygen from the compound.
This means extraction is a reduction process.

Extracting a metal from its oxide ore involves ____ oxygen, so it is $a ____$ process.

Reactivity Series and Extraction Method

The higher a metal is in the reactivity series, the more difficult it is to extract.
Metals above carbon must be extracted using electrolysis (e.g., aluminium).
Metals below carbon can be extracted by heating with carbon or carbon monoxide (e.g., iron).
Very unreactive metals like gold are found native (as uncombined elements).

Which of these are true?

Aluminium is extracted by heating with carbon.
Iron is extracted by reduction using carbon monoxide.
Gold is often found as a native metal.
Metals above carbon are extracted by electrolysis.

Extraction of Iron from Hematite

Iron is extracted in a blast furnace from its ore, hematite (iron(III) oxide).
Raw materials: iron ore, coke (carbon), and limestone are added at the top.
Hot air is blown into the bottom of the furnace.
Carbon monoxide reduces iron(III) oxide to iron: Fe₂O₃ + 3CO → 2Fe + 3CO₂.

What is the main reducing agent in the blast furnace?

Carbon (coke)
Carbon dioxide
Carbon monoxide
Limestone

Role of Limestone in Iron Extraction

Limestone (calcium carbonate) is added to remove impurities.
It thermally decomposes to calcium oxide and carbon dioxide.
Calcium oxide reacts with silicon dioxide (impurity) to form calcium silicate (slag).
Slag floats on molten iron and is tapped off separately.

Limestone decomposes to calcium oxide $and ____$ . Calcium oxide then reacts with $____ to$ form slag.

Extraction of Aluminium from Bauxite

Aluminium is above carbon in the reactivity series, so it cannot be extracted by reduction with carbon.
It is extracted by electrolysis of molten aluminium oxide (bauxite).
Aluminium oxide is dissolved in molten cryolite to lower the melting point.
Aluminium forms at the cathode and oxygen at the anode.

Why is aluminium extracted by electrolysis rather than by heating with carbon?

Aluminium is too expensive to heat with carbon
Aluminium is more reactive than carbon
Aluminium oxide is not reduced by carbon monoxide
Aluminium has a high melting point

Summary of Extraction Methods

Metals above carbon (e.g., Al) are extracted by electrolysis.
Metals below carbon (e.g., Fe, Zn) are extracted by reduction with carbon or carbon monoxide.
Very unreactive metals (e.g., Au, Pt) are found native.
The method depends on the metal's position in the reactivity series.

Which of these are correctly matched?

Aluminium – electrolysis
Iron – reduction with carbon monoxide
Gold – electrolysis
Zinc – found native

Flashcards

What is a metal ore?

A rock that contains enough of the metal to make it worthwhile extracting.

Why is the extraction of a metal from its oxide ore a reduction process?

Because oxygen is removed from the metal compound.

What are native metals? Give two examples.

Very unreactive metals found as uncombined elements. Examples: gold and platinum.

How does the position of a metal in the reactivity series affect its extraction method?

Metals above carbon must be extracted by electrolysis; metals below carbon can be extracted by heating with carbon or carbon monoxide.

Which metal is commonly extracted by electrolysis?

Aluminium.

Which metal is commonly extracted in a blast furnace?

Iron.

What are the raw materials added to the top of a blast furnace?

Iron ore (hematite), coke (impure carbon), and limestone.

What is the purpose of hot air blown into the bottom of a blast furnace?

To burn coke, producing heat and carbon dioxide.

Write the equation for the burning of coke in the blast furnace.

$C + O2$ → CO2

What is the main reducing agent in the blast furnace?

Carbon monoxide (CO).

Write the equation for the formation of carbon monoxide in the blast furnace.

$CO2 + C$ → 2CO

Write the equation for the reduction of iron(III) oxide by carbon monoxide.

$Fe2O3 + 3CO$ → $2Fe + 3CO2$

What is the purpose of limestone in the blast furnace?

To remove impurities (silicon dioxide) from the iron ore.

Write the equation for the thermal decomposition of limestone.

CaCO3 → $CaO + CO2$

Write the equation for the formation of slag in the blast furnace.

$CaO + SiO2$ → CaSiO3

What is slag and how is it removed?

Molten calcium silicate that floats on top of molten iron and is tapped off separately.

Why is aluminium not extracted by reduction with carbon?

Because aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide.

How is aluminium extracted from its ore?

By electrolysis of aluminium oxide dissolved in molten cryolite.

What is the ore of aluminium called?

Bauxite (contains aluminium oxide).

Why is cryolite used in aluminium extraction?

To lower the melting point of aluminium oxide, making electrolysis more economical.

What is produced at the cathode during aluminium electrolysis?

Molten aluminium metal.

What is produced at the anode during aluminium electrolysis?

Oxygen gas (which reacts with the carbon anode to form CO2).

Why is electrolysis an expensive method of extraction?

It requires a large amount of electricity.

Which metals are often found native?

Very unreactive metals such as gold and platinum.

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