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12.4Chapter 12: Chemical Reactions 3 and Rates

Extracting metals — Alhussan Chemistry - Stage 9 Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 13 2 quizzes

📚 Alhussan Chemistry - Stage 9 Hub / Topical Revision
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Lesson summary

12.4 Extracting metals — Ores, Carbon Reduction and Electrolysis — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define ore and link the position of a metal in the reactivity series to how it is extracted.Compounds in rocks — in the Earth's crust most metals are …

  • Native metals
  • Carbon in the series
  • Below carbon
  • Above carbon
  • Blast furnace
  • Oxidation and reduction

Part 1 of 7Ores

Compounds in rocks
  • Compounds in rocks in the Earth's crust most metals are joined to other elements in compounds mixed with other substances.
Ore
Ore a rock that a metal can be extracted from, containing enough metal compound to be worth extracting.
  • Iron is found as haematite (iron oxide), aluminium as bauxite (aluminium oxide), copper in malachite (copper carbonate) and lead as lead sulfide.
Native metals
  • Native metals unreactive metals such as gold can be found as the metal itself.
Reduction
Reduction removing oxygen (or the non-metal) from a compound to get the metal.

Part 2 of 7Extraction and the reactivity series

Carbon in the series
  • Carbon in the series carbon is a non-metal but can be placed in the series between aluminium and zinc.
Below carbon
  • Below carbon zinc, lead, iron, copper and silver are extracted from their oxides by heating with carbon, which is cheap and easy to obtain.
Above carbon
  • Above carbon sodium, calcium, magnesium and aluminium are extracted by electrolysis.
PositionMethodExamples
Above carbonElectrolysisPotassium, sodium, calcium, magnesium, aluminium
Below carbonHeating with carbonZinc, iron, lead
Very lowFound native or by simple separationGold, silver

Part 3 of 7Extracting iron with carbon

Extracting iron with carbon
Separate iron oxide from the compounds it is mixed with.
Heat the iron oxide with carbon (charcoal or coke): iron oxide + carbon → iron + carbon dioxide.
Blast furnace
  • Blast furnace iron ore, coke and limestone are fed in at the top and hot air is blown in near the bottom.
  • Coke burns to carbon dioxide, which reacts with more coke to form carbon monoxide.
  • Carbon monoxide reduces iron oxide to molten iron: iron oxide + carbon monoxide → iron + carbon dioxide.
  • Limestone removes impurities such as sand by forming slag, which floats on the iron and is tapped off.
Oxidation and reduction
  • Oxidation and reduction iron oxide is reduced (loses oxygen) and carbon is oxidised (gains oxygen).
Use
  • Use iron is made into steel by adding other elements, and the 55 km Hong Kong-Zhuhai-Macau Bridge, the longest sea-crossing bridge, is made of steel.
Cost and environment
  • Cost and environment the process is relatively cheap, but it releases carbon dioxide, a greenhouse gas.

Part 4 of 7Extracting lead

  • Source
    • lead exists as lead sulfide in the crust, and people have used lead for up to 8000 years.
Extracting lead
Heat lead sulfide in air: lead sulfide + oxygen → lead oxide + sulfur dioxide.
Heat the lead oxide with carbon: lead oxide + carbon → lead + carbon dioxide.
  • Uses
    • lead is now used for roofing and to protect from X-rays.

Part 5 of 7Extracting reactive metals by electrolysis

  • Aluminium
    • carbon cannot remove oxygen from aluminium oxide, so electricity is used instead.
Extracting reactive metals by electrolysis
Dissolve pure aluminium oxide in a special solvent (molten cryolite), which lowers the melting temperature and saves energy.
Pass a very large electric current (about 100 000 amps) through the solution to split up the aluminium oxide.
Liquid aluminium forms at the negative carbon electrode and oxygen at the positive electrode.
Carbon anodes
  • Carbon anodes the oxygen burns away the carbon anodes, so they must be replaced regularly.
Electrolysis in general
  • Electrolysis in general positive metal ions move to the negative electrode (cathode) and gain electrons to form the metal.
  • Other reactive metals are extracted this way, for example sodium from molten sodium chloride.
Cost
  • Cost electrolysis uses a great deal of electricity, which is why aluminium is made near sources of cheap power.

Part 6 of 7Extracting gold

Native gold
  • Native gold gold is at the bottom of the series, is unreactive and is found as the element.
Panning
  • Panning gold in stream beds mixed with sand and gravel is separated by placing the mixture in a pan with water,
  • because gold has a higher density and sinks to the bottom.

Part 7 of 7Sustainability

Mining
  • Mining it takes land, uses energy and may pollute.
Recycling
  • Recycling it saves ores and energy;
    • recycling aluminium needs only about 5% of the energy of making it from ore.
Balance
  • Balance governments and industry balance economic needs with environmental effects.

Key terms

TermMeaning
Orea rock from which a metal can be extracted for profit.
Reductionthe loss of oxygen from a compound.
Electrolysisbreaking down a molten or dissolved ionic compound using electricity.
Native metala metal found uncombined in nature.
Slagwaste formed in the blast furnace from impurities and limestone.
Bauxitethe ore of aluminium, mainly aluminium oxide.

Avoid these mistakes

1
Saying that carbon reduces all metal oxides — it cannot reduce oxides of metals above carbon.
2
Saying electrolysis is cheap — it uses a lot of electricity.
3
Mixing up oxidation and reduction — reduction is loss of oxygen and oxidation is gain of oxygen.
4
Saying the ore is the pure metal — an ore is a rock containing a metal compound.

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