Chemical changes · GCSE Chemistry
Metal extraction
GCSE Chemistry revision on metal extraction: native metals, reduction of oxides with carbon, electrolysis for metals above carbon, and phytomining or bioleaching for copper.
Unreactive metals: found native. Metals below carbon: heat the oxide with carbon. Metals above carbon: electrolysis of a molten compound. Copper can also be leached or grown in plants, then displaced or electrolysed.
The important bits
What you need to know
- 1
A metal ore contains enough of the metal compound to extract the metal economically. Haematite is mainly Fe₂O₃; bauxite is aluminium oxide; rocksalt is NaCl.
- 2
Gold and silver can be found native (uncombined) because they are very unreactive. Most other metals are found as oxides, sulfides or carbonates.
- 3
Metals less reactive than carbon (zinc, iron, lead, copper) can be extracted by heating the oxide with carbon: the carbon reduces the oxide and is oxidised to CO₂ or CO.
- 4
Blast furnace: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Carbon monoxide is the reducing agent. Limestone removes acidic impurities as slag (calcium silicate).
- 5
Metals more reactive than carbon (K, Na, Ca, Mg, Al) are extracted by electrolysis of a molten ionic compound. That needs a lot of electrical energy, so it is expensive.
- 6
Sulfide ores are often roasted first to make the oxide, then reduced. This produces SO₂, which must be handled to avoid acid rain.
- 7
Low-grade copper ores: phytomining (plants absorb copper compounds, are harvested and burned, copper is recovered from the ash) and bioleaching (bacteria produce a leachate of copper ions).
- 8
Copper ions in solution are displaced by scrap iron (Fe + Cu²⁺ → Fe²⁺ + Cu) or purified by electrolysis. Recycling metals saves energy and ore, but needs collection and sorting.
Quotations worth analysing
Short evidence. Real method.
“2Fe₂O₃(s) + 3C(s) → 4Fe(l) + 3CO₂(g) or Fe₂O₃ + 3CO → 2Fe + 3CO₂”
Carbon or carbon monoxide gains oxygen (is oxidised); iron oxide loses oxygen (is reduced). On Higher tier, reduction is also gain of electrons by Fe³⁺.
“Metals above carbon in the reactivity series are extracted by electrolysis.”
Carbon is not a strong enough reducing agent to pull oxygen off Al₂O₃ or NaCl in a useful way. Electricity supplies the electrons instead.
“Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s)”
A cheaper, more reactive metal wins the copper from bioleachate or phytomining ash dissolved as Cu²⁺. This links extraction to the reactivity series.
Go deeper
Choose the method from the series, then name the redox
Look at the metal’s position relative to carbon. Below carbon: reduction with carbon is possible and relatively cheap. Above carbon: electrolysis, expensive because of melting and electricity. Native: no compound to reduce. Then name what is oxidised and what is reduced. In Fe₂O₃ + 3CO → 2Fe + 3CO₂, iron oxide is reduced (loses oxygen) and CO is oxidised (gains oxygen). Electron view: Fe³⁺ gains electrons to become Fe. Students write “iron is oxidised because it is extracted” — that is backwards. The metal ion is reduced to the metal.
Go deeper
New methods exist because high-grade ores run out
Phytomining uses plants that accumulate copper. Burning them gives an ash rich in copper compounds, which you dissolve and then displace or electrolyse. Bioleaching uses bacteria to dissolve copper compounds from low-grade ore, producing a leachate of Cu²⁺. Both avoid large-scale digging and roasting, so they can have a smaller environmental impact, but they are slow. Evaluation questions want a benefit (low-grade ore, less SO₂ from roasting) and a drawback (slow, still need energy later, land use for plants). Do not claim they use no energy. Scrap iron still has to reduce Cu²⁺ to copper metal afterwards.
Go deeper
Recycling is an energy and environment calculation
Recycling aluminium uses a small fraction of the energy of extracting it from bauxite by electrolysis, and it saves bauxite landscapes. Scrap steel goes back to the furnace. Drawbacks: collection, sorting different alloys, and sometimes lower quality if impurities remain. A six-mark “evaluate extracting versus recycling” should mention finite ores, energy, carbon dioxide from electricity generation, and the usefulness of the metal. Link aluminium specifically to the electrolysis page: the carbon anodes and cryolite are part of the cost you avoid when you recycle a can. That is why drinks-can recycling appears in life-cycle questions too.
See the idea in action
Explain why iron is extracted in a blast furnace but aluminium is not, and how copper can be obtained from a low-grade ore. Iron is less reactive than carbon, so Fe₂O₃ is reduced by CO: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Aluminium is more reactive than carbon, so Al₂O₃ must be electrolysed (dissolved in molten cryolite). For low-grade copper, bacteria can leach Cu²⁺ (bioleaching), then scrap iron displaces copper: Fe + Cu²⁺ → Fe²⁺ + Cu. Iron oxide was reduced; aluminium ions would be reduced at a cathode instead.
Exam technique
Turn knowledge into marks
State the metal’s position relative to carbon, name the method, then say what is reduced. For copper, mention phytomining or bioleaching plus displacement or electrolysis. For evaluation, give one environmental benefit and one limitation.
Common mistakes
Do not give these marks away
- 01
Saying aluminium is extracted with carbon, or that iron is extracted by electrolysis in the blast furnace.
- 02
Calling the extracted metal oxidised, rather than the metal ions reduced.
- 03
Claiming phytomining uses no energy, or forgetting that bioleaching still produces Cu²⁺ that must be turned into copper metal.
Why is aluminium extracted by electrolysis rather than by heating with carbon?
AAluminium is less reactive than carbon
BAluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide
CAluminium oxide is not ionic
DElectrolysis is always cheaper than using carbon
Show the answer
Aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide. Metals above carbon need electrolysis of a molten compound. Carbon is a strong enough reducing agent for iron oxide, but not for aluminium oxide in this process.
Quick questions
If this is the bit you searched
How is iron extracted in the blast furnace GCSE Chemistry?
Haematite (Fe₂O₃) is reduced by carbon monoxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Limestone removes impurities as slag. Iron is less reactive than carbon.
Which metals are extracted by electrolysis?
Metals more reactive than carbon, including potassium, sodium, calcium, magnesium and aluminium. The process uses a molten ionic electrolyte.
What is bioleaching?
Using bacteria to dissolve metal compounds from low-grade ore, producing a solution of metal ions such as Cu²⁺, which are then displaced or electrolysed.
Why is recycling aluminium worthwhile?
Electrolysis of aluminium oxide uses a large amount of electrical energy. Recycling aluminium metal avoids most of that energy cost and saves bauxite ore.