4.2.1Guiding Spaceship Earth Towards a Sustainable Future
Metal Extraction By Reduction Of Oxides — AQA GCSE Combined Science Synergy 8465 - Physical Sciences Revision Notes & Topical Questions
5 min read 8 parts Lesson 7 of 15
Part 1 of 6Ores and reduction
Ores
- Ores An ore is a rock containing enough of a metal compound for the metal to be extracted at a profit.
- Many metals are found combined with oxygen as oxides, while others occur as sulfides or carbonates that are first converted to oxides.
Reduction
- Reduction Reduction can mean removal of oxygen.
- A metal oxide is reduced when it loses oxygen to form the metal.
- Gain of electrons is the same process described in terms of electron transfer: the metal ions gain electrons to become atoms.
Unreactive metals
- Unreactive metals Gold and platinum are so unreactive that they occur as the native metal,
- so they only need to be separated from rock and do not need a chemical reaction.
Economic decision
- Economic decision Whether it is worth extracting a metal depends on the percentage of metal in the ore, the cost of energy and the price the metal can be sold for.
Part 2 of 6Using the reactivity series
| Position | Method of extraction | Examples |
|---|---|---|
| Above carbon | Electrolysis of the molten compound, because carbon is not reactive enough to remove the oxygen | Potassium, sodium, calcium, magnesium, aluminium |
| Below carbon | Heating the oxide with carbon, which takes the oxygen away | Zinc, iron, tin, lead, copper |
| Very unreactive | Found uncombined in the Earth, so no reduction is needed | Gold, platinum |
Part 3 of 6Extracting iron in the blast furnace
1
Iron(III) oxide (from haematite), coke (carbon), limestone and hot air are fed into the furnace.
2
Coke burns in the hot air blast: C + O2 → CO2, releasing a large amount of heat that keeps the furnace hot.
3
Carbon dioxide reacts with more coke higher up: CO2 + C → 2CO, making the main reducing agent.
4
Carbon monoxide reduces the iron oxide: Fe2O3 + 3CO → 2Fe + 3CO2.
5
Limestone decomposes to calcium oxide, which reacts with acidic impurities such as silica to form molten slag: CaO + SiO2 → CaSiO3.
6
Molten iron is denser than the slag, so it sinks to the bottom and is tapped off, with the slag floating above it.
Part 4 of 6Why carbon works
1Carbon is more reactive
- Carbon is more reactive It sits above the metal in the reactivity series, so it has a stronger attraction for oxygen.
2It takes the oxygen
- It takes the oxygen Carbon displaces the less reactive metal from its oxide when the two are heated together.
3Metal is released
- Metal is released The oxide is reduced and carbon is oxidised, forming carbon dioxide (or carbon monoxide) as a gas that escapes.
Part 5 of 6Worked examples of reduction with carbon
| Metal oxide | Equation | What is reduced / oxidised |
|---|---|---|
| Zinc oxide | 2ZnO + C → 2Zn + CO2 | ZnO is reduced; carbon is oxidised |
| Copper(II) oxide | 2CuO + C → 2Cu + CO2 | CuO is reduced; carbon is oxidised |
| Lead(II) oxide | 2PbO + C → 2Pb + CO2 | PbO is reduced; carbon is oxidised |
| Aluminium oxide | No reaction with carbon | Aluminium is more reactive than carbon, so electrolysis is used |
Part 6 of 6Evaluating the blast furnace
Iron extraction in industry
Raw materials are cheap
- Raw materials are cheap Haematite, coke, limestone and air are all widely available, which keeps the cost of iron low.
Continuous process
- Continuous process Materials are added at the top and products removed at the bottom without stopping the furnace for months.
Environmental impact
- Environmental impact Large amounts of carbon dioxide are released, and mining and slag disposal damage the landscape.
Waste heat
- Waste heat Hot waste gases are used to pre-heat the incoming air, which saves fuel and money.
Key terms
| Term | Meaning |
|---|---|
| Ore | A rock containing a metal or metal compound in a high enough amount to extract economically. |
| Reduction | Loss of oxygen from a compound (or gain of electrons). |
| Oxidation | Gain of oxygen by a substance (or loss of electrons). |
| Reactivity series | A list of metals in order of how readily they react. |
| Slag | A waste material formed when limestone reacts with impurities in the blast furnace. |
| Reducing agent | A substance that removes oxygen from another substance and is itself oxidised, such as carbon monoxide in the blast furnace. |
Avoid these mistakes
1
Using carbon to extract aluminium. Aluminium is more reactive than carbon, so electrolysis is needed.
2
Saying the metal oxide is oxidised. It is reduced, while the carbon is oxidised.
3
Writing that limestone is the main reducing agent in the blast furnace; carbon monoxide is.
4
Describing coke as only a fuel when it is also a source of the reducing agent.
5
Thinking all metals are extracted by heating with carbon.
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