Extraction Of Metals

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Metals and Ores

The Earth’s crust contains metals and metal compounds.
A metal ore is a rock that contains enough of the metal to make extraction worthwhile.
Many metal ores are oxides (e.g., hematite for iron, bauxite for aluminium).
Extraction is a reduction process because oxygen is removed from the ore.
Very unreactive metals like gold and platinum are found native (as uncombined elements).

Reactivity Series and Extraction Method

The extraction method depends on the metal's position in the reactivity series.
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).
Metals lower in the series are easier to extract than those higher up.
Electrolysis uses large amounts of electricity, making it expensive.

Extraction of Iron from Hematite – Blast Furnace

Iron is extracted from its ore hematite (Fe₂O₃) in a blast furnace.
Raw materials: iron ore, coke (impure carbon), and limestone (CaCO₃).
Hot air is blown into the bottom of the furnace.

The blast furnace

Reactions in the Blast Furnace (Extended)

Zone 1: Coke burns: C + O₂ → CO₂ (exothermic, provides heat).
Zone 2: CO₂ + C → 2CO (carbon monoxide is the main reducing agent).
Zone 3: Fe₂O₃ + 3CO → 2Fe + 3CO₂ (reduction of iron ore).
Limestone decomposes: CaCO₃ → CaO + CO₂ (thermal decomposition).
CaO removes SiO₂ impurity: CaO + SiO₂ → CaSiO₃ (slag).
Molten iron is tapped from the bottom; slag floats on top and is removed separately.

Extraction of Aluminium from Bauxite – Electrolysis

Aluminium is extracted from bauxite (Al₂O₃) by electrolysis.
Aluminium is above carbon in the reactivity series, so carbon reduction is not possible.
Al₂O₃ is dissolved in molten cryolite to lower the melting point (from >2000°C to ~950°C).
The electrolysis cell has a graphite lining (cathode) and graphite anodes.
At cathode: Al³⁺ + 3e⁻ → Al (reduction).
At anode: 2O²⁻ → O₂ + 4e⁻ (oxidation).
Overall: 2Al₂O₃ → 4Al + 3O₂.
Oxygen reacts with the carbon anodes to form CO₂, so anodes wear away and must be replaced.

Electrolysis of aluminium oxide

Key Points for Exams

Remember OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
For iron extraction, know the three zones and the role of limestone.
For aluminium, explain why cryolite is used and why anodes need replacing.
Unreactive metals (Cu, Ag, Au) may be found native or extracted by simple heating.

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Câu hỏi luyện tập

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1.Which of the following is the main ore of aluminium?
Easy
- ABauxite
- BHematite
- CMalachite
- DLimestone
2.Which of the following metals is found native (as the uncombined element) in the Earth's crust?
Easy
- AGold
- BIron
- CAluminium
- DZinc
3.What is the main reducing agent in the blast furnace for the extraction of iron?
Easy
- ACarbon monoxide
- BCarbon dioxide
- CCoke
- DLimestone
4.In the extraction of aluminium by electrolysis, why is aluminium oxide dissolved in molten cryolite?
Medium
- ATo lower the melting point of the mixture
- BTo provide a source of aluminium ions
- CTo act as a reducing agent
- DTo increase the conductivity of the solution
5.In the blast furnace, which substance is added to remove impurities such as silicon dioxide?
Easy
- ALimestone
- BCoke
- CIron ore
- DCarbon monoxide
6.Which of the following statements about transition elements is correct?
Easy
- ATheir compounds are highly coloured
- BThey have low melting points
- CTheir compounds are colourless
- DThey have only one oxidation state
7.The overall equation for the extraction of aluminium is 2Al2O3 → 4Al + 3O2. At the anode, oxygen reacts with the graphite electrodes. What is the main reason the anodes need to be replaced periodically?
Medium
- AThe graphite reacts with oxygen to form CO2, wearing away the anode
- BThe aluminium produced attacks the anode
- CThe cryolite dissolves the graphite
- DThe high temperature melts the graphite
8.In the blast furnace, which reaction is an example of thermal decomposition?
Easy
- ACaCO3 → CaO + CO2
- BC + O2 → CO2
- CCO2 + C → 2CO
- DFe2O3 + 3CO → 2Fe + 3CO2

Thêm câu hỏi

9.Which of the following metals is extracted by reduction with carbon?
Easy
- AIron
- BAluminium
- CSodium
- DPotassium
10.Why is aluminium not extracted by reduction with carbon?
Easy
- AAluminium is above carbon in the reactivity series
- BAluminium is too expensive
- CAluminium oxide is not an ore
- DCarbon reacts explosively with aluminium
11.In the electrolysis of aluminium oxide, what is produced at the negative electrode (cathode)?
Easy
- AAluminium
- BOxygen
- CCarbon dioxide
- DCryolite
12.In the blast furnace, the reaction Fe2O3 + 3CO → 2Fe + 3CO2 shows that iron(III) oxide is reduced. What is the reducing agent?
Easy
- ACarbon monoxide
- BIron(III) oxide
- CIron
- DCarbon dioxide
13.In a blast furnace, the reaction CaCO3 → CaO + CO2 occurs. Which type of reaction is this?
Easy
- AThermal decomposition
- BCombustion
- CReduction
- DOxidation
14.The table shows how metals in different positions in the reactivity series are extracted (from the source material). | Reactivity | Metals | Method of extraction | |---|---|---| | Above carbon | Aluminium | Electrolysis of molten compounds | | Below carbon | Iron, Zinc | Heating with carbon or carbon monoxide | | Very unreactive | Copper | Found native or needs little processing | Which of the following is correctly matched with its extraction method?
Medium
- AAluminium - electrolysis
- BIron - electrolysis
- CZinc - electrolysis
- DCopper - reduction with carbon
15.A student is given a sample of an unknown metal ore. The ore is heated strongly with carbon and a metal is produced. Which metal could NOT be extracted by this method?
Medium
- AAluminium
- BZinc
- CIron
- DCopper
16.In the blast furnace, what is the purpose of adding limestone (calcium carbonate)?
Easy
- ATo remove impurities such as silicon dioxide
- BTo provide heat by burning
- CTo reduce iron(III) oxide to iron
- DTo increase the concentration of iron ore
17.During the electrolysis of aluminium oxide dissolved in molten cryolite, the reaction at the cathode is Al3+ + 3e- → Al. What is the correct description of this process?
Medium
- AReduction, because aluminium ions gain electrons
- BOxidation, because aluminium ions gain electrons
- CReduction, because aluminium ions lose electrons
- DOxidation, because aluminium ions lose electrons
18.How does increasing the carbon content of iron produced in the blast furnace affect its malleability?
Medium
- AMalleability decreases as carbon content increases
- BMalleability increases as carbon content increases
- CMalleability is highest at around 2% carbon
- DMalleability is unaffected by carbon content
19.Which of the following is the main ore of iron?
Easy
- AHematite
- BBauxite
- CMalachite
- DLimestone
20.In the laboratory, a student wants to obtain a sample of copper metal from malachite (copper carbonate). Which of the following sequences of steps is correct?
Medium
- ACrush the malachite, heat it strongly, then reduce the copper oxide with carbon.
- BDissolve the malachite in water, then electrolyze the solution.
- CHeat the malachite with carbon directly to obtain copper.
- DAdd acid to the malachite, then add zinc to displace copper.
21.Which of the following reactions in the blast furnace is an example of thermal decomposition?
Easy
- AC + O2 → CO2
- BCO2 + C → 2CO
- CCaCO3 → CaO + CO2
- DFe2O3 + 3CO → 2Fe + 3CO2
22.In the extraction of iron, the reaction Fe2O3 + 3CO → 2Fe + 3CO2 shows that iron(III) oxide is reduced. What is the reducing agent?
Easy
- AIron(III) oxide
- BCarbon monoxide
- CIron
- DCarbon dioxide
23.Which statement about the extraction of metals is correct?
Medium
- AMetals above carbon in the reactivity series are extracted by reduction with carbon.
- BMetals below carbon in the reactivity series are extracted by electrolysis.
- CMetals above carbon in the reactivity series are extracted by electrolysis.
- DAll metals are extracted by reduction with carbon.
24.During the electrolysis of aluminium oxide, what is produced at the positive electrode (anode)?
Easy
- Aaluminium
- Boxygen
- Ccarbon dioxide
- Dcryolite
25.Which of the following is a raw material added to the blast furnace for iron extraction?
Easy
- Ahematite
- Bcryolite
- Cbauxite
- Dsodium chloride
26.In the extraction of iron, what is the name of the molten waste product formed from impurities?
Easy
- Aslag
- Bcoke
- Cflux
- Dgangue
27.Which of the following statements about the extraction of aluminium is correct?
Medium
- AAluminium is extracted by reduction with carbon because it is below carbon in the reactivity series.
- BThe overall reaction is 2Al₂O₃ → 4Al + 3O₂, and the carbon anodes are consumed because oxygen reacts with them.
- CCryolite is added to increase the melting point of the mixture.
- DAluminium is produced at the positive electrode (anode).
28.In the blast furnace, the reaction CaCO3 → CaO + CO2 occurs. What is the purpose of this reaction?
Medium
- ATo provide heat for the furnace
- BTo produce calcium oxide which removes impurities
- CTo produce carbon dioxide which reduces iron oxide
- DTo produce carbon monoxide which reduces iron oxide
29.A blast furnace produces 10,000 tonnes of iron per day. If the iron ore (hematite, Fe2O3) is 70% pure, what mass of ore is needed per day to produce this amount of iron? (Ar: Fe=56, O=16)
Hard
- A14,286 tonnes
- B20,408 tonnes
- C24,490 tonnes
- D28,571 tonnes
30.The extraction of a metal from its oxide ore is an oxidation process.
Easy
True or false?
31.In the blast furnace, limestone is added to remove silicon dioxide impurities by forming calcium silicate (slag).
Easy
True or false?
32.In the blast furnace, the reaction C + CO₂ → 2CO is an example of reduction.
Medium
True or false?
33.Match each raw material in the blast furnace to its role.
Easy
- Iron ore (hematite)
- Coke
- Limestone
- Provides iron(III) oxide
- Provides carbon and heat
- Removes impurities
34.Match each raw material in the blast furnace to its correct role.
Easy
- Iron ore (hematite)
- Coke
- Limestone
- Provides iron(III) oxide
- Produces reducing agent and heat
- Removes impurities as slag
35.Arrange the following steps in the correct order for the extraction of iron in the blast furnace.
Medium
- Coke burns to form CO2
- CO reduces Fe2O3 to Fe
- C + CO2 → 2CO
- Limestone decomposes to CaO and CO2
36.Which of the following statements about the extraction of aluminium are correct? (Select all that apply.)
Hard
- AAluminium is extracted by electrolysis of molten aluminium oxide.
- BAluminium oxide is dissolved in molten cryolite to lower the melting point.
- CThe cathode is made of graphite and is consumed during the process.
- DOxygen gas is produced at the anode.
- EThe overall reaction is 2Al2O3 → 4Al + 3O2.
37.Complete the sentence.
Easy
A metal ore is a rock that contains enough of the metal to make it ____ extracting.
38.Name the three raw materials added to the top of the blast furnace.
Easy
The three raw materials added to the top of the blast furnace are ____, ____, and ____.
39.Complete the half-equation at the cathode during the electrolysis of aluminium oxide.
Medium
At the cathode: ____ + 3e⁻ → ____
40.State what is meant by the term 'native metal'.
Easy
41.Complete the sentence about the extraction of iron.
Medium
In the blast furnace, the main reducing agent is ____ . It is formed by the reaction between ____ and ____ .
42.In the electrolysis of aluminium oxide, if a current of 100,000 A is passed for 24 hours, and the charge of one mole of electrons is 96,500 C, calculate the mass of aluminium produced (in tonnes). The molar mass of Al is 27 g/mol. (Assume 100% efficiency and that the only reaction at the cathode is Al3+ + 3e- → Al.)
Hard
43.In the electrolysis of aluminium oxide, if a current of 100,000 A is passed for 24 hours, and the charge of one mole of electrons is 96,500 C, calculate the mass of aluminium produced (in tonnes). The molar mass of Al is 27 g/mol. (Assume 100% efficiency and that the only reaction at the cathode is Al3+ + 3e- → Al.)
Hard
- A1.805 tonnes
- B-0.195 tonnes
- C0.805 tonnes
- D2.805 tonnes

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