Extraction method vs reactivity
Most metals occur in ores; a few unreactive metals (e.g. gold) are found native (uncombined). Extraction removes the metal from its compound and is a reduction (the metal ion gains electrons). Metals more reactive than carbon (e.g. aluminium) are extracted by electrolysis of the molten compound; those less reactive by reduction with carbon. Carbon reduction is cheaper (electricity is expensive), so it is used for metals below carbon.
Iron in the blast furnace
Blast furnace: carbon (coke) burns to carbon dioxide, ; this reacts with more hot carbon to carbon monoxide, . Carbon monoxide is the reducing agent, removing oxygen: . The iron is reduced (loses oxygen); the CO is oxidised. Write and balance these reduction equations.
Aluminium by electrolysis; alloys
Aluminium is above carbon, so carbon cannot reduce it — it is extracted by electrolysis of molten aluminium oxide: . This is expensive. Uses (2.25C): aluminium — aircraft/cables (low density, corrosion-resistant); copper — wiring (good conductor). An alloy is a mixture of a metal with other elements; alloys are harder than pure metals because different-sized atoms distort the layers so they cannot slide.
Drawn from real examiner reports.
Extraction is reduction, not oxidation
Extracting a metal from its ore is a reduction, not an oxidation. Define reduction as gain of electrons (and also loss of oxygen): gains electrons to become an atom. Writing only "loss of oxygen" is the narrow form and can miss the electron-transfer mark. The reducing agent (carbon / carbon monoxide) is itself oxidised.
June 2023 Paper 2C: candidates lost marks for narrow or wrong-direction reduction/oxidation definitions, and for treating a metal-from-oxide change as adding oxygen.
Write "graphite", not "carbon"
In aluminium electrolysis, writing "carbon" instead of "graphite" for the electrode loses the mark — carbon could mean diamond or charcoal (ambiguous), whereas graphite is the named form that conducts and withstands the conditions. Always specify graphite for the electrode.
June 2024 Paper 2C: candidates who wrote carbon instead of graphite for the electrode lost the mark.
Balance reduction equations fully
In reduction equations such as , candidates often give the correct products but leave the equation unbalanced — the second mark is only for a fully balanced equation. Check every element balances before moving on.
June 2024 and June 2023 Paper 2C: reduction equations had correct products but were left unbalanced, losing the equation mark.
Aluminium is not unreactive
When explaining aluminium uses, do not say it "does not react". Aluminium is quite reactive but resists corrosion because a thin, tough layer of aluminium oxide forms on its surface and seals the metal beneath. State the oxide layer, not "unreactive".
(common Edexcel chemistry error)
Sacrificial protection: more reactive metal
Sacrificial protection needs a metal MORE reactive than iron (higher in the series), so it is oxidised instead of the iron. Candidates lose marks by not connecting a more reactive metal to the iron, or by describing a barrier method (paint, plating) instead — a barrier is a different idea.
June 2024 Paper 2C: candidates failed to connect a more reactive metal to the iron, or described a barrier method instead.
An alloy is a mixture, not a compound
An alloy is a MIXTURE of a metal with one or more other elements (metals or carbon) — the components are not chemically combined in fixed proportions. Do not call an alloy a compound. This is why an alloy composition can be varied to tune its properties.
(common Edexcel chemistry error)
Carbon cut-off chooses the method
To choose an extraction method: is the metal above carbon (K, Na, Ca, Mg, Al) or below (Zn, Fe, Cu)? Above -> electrolysis of the molten compound; below -> carbon reduction. Electrolysis is dearer, so it is used only when carbon cannot reduce the metal.
"Comment on the process": use the data
For "comment on this process" (2.24C) you are given the information — you do not need memorised process detail. Read the data, identify what is reduced (loses oxygen / gains electrons), and write a balanced equation, adding state symbols (s)/(l)/(g) where asked.
Extraction reacting-mass steps
For an extraction mass question on : moles = mass ÷ Mr, apply the mole ratio (1:2, :Fe), then mass = moles × Ar. E.g. 160 g (Mr 160) -> 2 mol Fe = 112 g.
Uses: link the property to the use
For a "uses of metals" question, give the PROPERTY then the use it enables: aluminium — low density, corrosion-resistant -> aircraft, cables; copper — good conductor, ductile -> wiring; steel — strong -> bridges, tools. Always link property to use, not just name a use.
The method depends on the metal's position relative to carbon in the reactivity series:
| Metal vs carbon | Method | Example | Why |
|---|---|---|---|
| More reactive (above carbon) | Electrolysis of molten compound | Aluminium | Carbon cannot reduce it; needs electricity |
| Less reactive (below carbon) | Reduction with carbon / carbon monoxide | Iron, zinc, copper | Carbon displaces the metal from its oxide — cheaper |
Key relationship for any "comment on the process" calculation: amount in moles , where = mass (g) and = relative formula mass.
Define an ore.
Zinc lies below carbon in the reactivity series. State the method used to extract zinc from zinc oxide, and explain why this method is chosen rather than electrolysis.
