Metals: IGCSE Chemistry 0620
Metals for IGCSE Chemistry 0620: reactivity series, iron and aluminium extraction, rusting prevention and alloys, taught the way examiners mark it.
The IGCSE Chemistry Specialist Team · founded by Rig
Written to the Cambridge IGCSE Chemistry (0620) syllabus and mark-scheme conventions. Last updated 2026-06-11.
Metals is the broadest topic in 0620 and one of the most heavily examined: expect 3-5 multiple choice marks plus structured questions on extraction or rusting worth 5-8 marks on Paper 3 or 4, and it is a favourite for the 6-mark extended response. Examiner reports flag the same failures every series: reactivity series out of order, blast furnace equations half-remembered, and “galvanising” described without the word sacrificial. The chemistry is connected; learn the reactivity series properly and the rest of the topic follows from it.
Properties of metals
Core recall: metals are good conductors of heat and electricity, malleable (hammered into shape) and ductile (drawn into wires), with high melting points and high density (Group I metals are the exception: see the Periodic Table). Non-metals are the mirror image: poor conductors, brittle as solids. The one chemical property tested here: metals form positive ions and their oxides are basic, while non-metal oxides are acidic.
The reactivity series
Learn it in order, including the two non-metals used as markers:
Potassium > sodium > calcium > magnesium > aluminium > (carbon) > zinc > iron > (hydrogen) > copper > silver > gold
Carbon’s position decides extraction method: metals below carbon can be extracted by heating their oxides with carbon; metals above carbon need electrolysis. Hydrogen’s position decides acid reactions: metals above hydrogen react with dilute acids to give hydrogen gas; copper, silver and gold do not.
The series also predicts displacement: a more reactive metal displaces a less reactive metal from a solution of its salt. Zinc placed in copper(II) sulfate solution becomes coated in red-brown copper and the blue colour fades:
Zn + CuSO4 → ZnSO4 + Cu
(S) Displacement is redox: zinc loses electrons (oxidation) and copper ions gain them (reduction). Writing the ionic equation Zn + Cu2+ → Zn2+ + Cu earns the Supplement mark.
Reactions of metals
Three reaction families, with vigour following the series:
- With water: potassium, sodium and calcium react with cold water to give the hydroxide and hydrogen. Magnesium reacts only slowly with cold water but rapidly with steam to give magnesium oxide and hydrogen.
- With dilute acids: metals above hydrogen give a salt and hydrogen. Mg + 2HCl → MgCl2 + H2. The fizzing gets weaker down the series and stops at copper.
- With oxygen: metals burn or tarnish to form the oxide; the more reactive, the more vigorous.
The exam skill is using observations to place an unfamiliar metal in the series: “metal X reacts with dilute acid but not with cold water. Place it between magnesium and copper, then narrow it down.”
Extraction of metals: iron and aluminium
Iron: the blast furnace. Raw materials: hematite (iron(III) oxide), coke (carbon), limestone (calcium carbonate) and hot air. The sequence of equations is the question:
- Coke burns in the hot air blast: C + O2 → CO2 (exothermic: this heats the furnace)
- Carbon dioxide is reduced by more coke: CO2 + C → 2CO
- Carbon monoxide reduces the ore: Fe2O3 + 3CO → 2Fe + 3CO2
- Limestone decomposes: CaCO3 → CaO + CO2, then the calcium oxide removes the acidic silica impurity: CaO + SiO2 → CaSiO3 (slag, which floats on the molten iron)
The reducing agent is carbon monoxide. Name it, not “carbon”, in equation 3.
Aluminium: electrolysis (S). Aluminium is above carbon, so its oxide cannot be reduced by carbon. Aluminium oxide from bauxite is dissolved in molten cryolite, which lowers the operating temperature and so reduces energy cost. At the carbon cathode: Al3+ + 3e− → Al. At the carbon anode: 2O2− → O2 + 4e−. The oxygen attacks the hot carbon anodes, forming CO2, so the anodes burn away and need regular replacement, a 2-mark favourite. The electrode chemistry belongs to electrochemistry, and revising the two together pays off.
Rusting and its prevention
Rusting needs both oxygen and water. The Core experiment with three test tubes (air + water rusts; boiled water under oil does not; dry air with calcium chloride does not) proves it. Prevention splits into two strategies:
- Barrier methods: paint, grease or plastic coating keep oxygen and water out. Cheap, but protection ends where the barrier is scratched.
- Sacrificial protection (S for the explanation): attach a more reactive metal, usually zinc. Zinc corrodes in preference to the iron because it loses electrons more readily. Galvanising combines both: a zinc barrier that also protects sacrificially at scratches.
Alloys and their uses
An alloy is a mixture of a metal with other elements (metals or carbon). Brass is copper and zinc; stainless steel is iron with chromium (and nickel), used for cutlery because it resists rusting; mild steel for car bodies and machinery. The explanation question: alloys are harder than pure metals because atoms of different sizes disrupt the regular layered arrangement, so the layers can no longer slide over each other. A labelled particle diagram (neat rows for the pure metal, disrupted rows for the alloy) can earn the marks on its own.
Worked exam question
Explain why aluminium is extracted by electrolysis but iron is extracted in the blast furnace, and state why the aluminium oxide is dissolved in molten cryolite. [4]
Model answer: Aluminium is more reactive than carbon / above carbon in the reactivity series (1), so carbon cannot reduce aluminium oxide (1). Iron is below carbon, so carbon monoxide reduces iron(III) oxide cheaply in the blast furnace (1). Cryolite lowers the temperature at which the electrolysis runs, reducing energy costs (1).
Mark-by-mark: M1 is the position comparison: “aluminium is very reactive” without the comparison to carbon scores nothing. M2 makes the consequence explicit: carbon cannot act as the reducing agent. M3 needs iron’s position and the named reducing agent. M4 is the cryolite mark, and “dissolves the ore” alone misses it. The scoring idea is lower operating temperature, hence lower energy cost.
The mistakes that cost marks
- Reactivity series in the wrong order. One misplaced metal collapses every prediction built on it. Test yourself cold until potassium-to-gold is automatic, with carbon and hydrogen slotted in.
- “Carbon reduces the iron oxide” in the blast furnace. The main reducing agent is carbon monoxide. Equation 3 with CO is the mark.
- Rusting answers naming only one condition. Oxygen and water are both required. “Air” is accepted for oxygen, but naming just water loses the mark.
- Sacrificial protection explained as a barrier. “The zinc covers the iron” misses the point. Zinc is more reactive, so it corrodes (loses electrons) in preference to iron. That is why protection survives scratches.
- Alloy hardness without particle language. “Alloys are stronger because they are mixed” scores zero. Different-sized atoms, disrupted layers, layers cannot slide: three ideas, usually two marks.
How to phrase it for full marks
| Student wording | Mark-scheme wording |
|---|---|
| ”Aluminium is too reactive for carbon" | "Aluminium is above carbon in the reactivity series, so carbon cannot reduce aluminium oxide" |
| "The zinc protects the iron" | "Zinc is more reactive than iron, so it corrodes in preference to the iron" |
| "Cryolite helps dissolve the ore" | "Molten cryolite lowers the operating temperature, reducing energy costs" |
| "Alloys are mixed so they’re stronger" | "Atoms of different sizes disrupt the layers, so the layers cannot slide over each other" |
| "Iron rusts in the rain" | "Rusting requires both oxygen and water” |
The pattern: every explanation in this topic runs through the reactivity series or through particle structure. Anchor the answer to one of those two and the marks follow. The most repeated slip-ups across the whole syllabus (including the blast furnace ones) are collected in our common exam mistakes guide.
The Malaysia note
Metals usually lands mid-Year 10 in Malaysian international schools, taught fast because the topic is long, and the blast furnace gets one lesson when it deserves three. Malaysian students sitting the May/June series tell us the same thing each year: they can recite the reactivity series but cannot use it to justify an extraction method under timed conditions. The link to corrosion is also local and concrete: coastal humidity in Penang and JB makes rusting questions easy to picture but no easier to phrase. We rebuild this topic around the series-first logic, and a free trial lesson is the quickest way to see whether your blast furnace answers would actually score.
Every sub-topic in Metals
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Frequently asked questions
Do I need to memorise the reactivity series for 0620?
Yes, in order: potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold. Carbon and hydrogen are included as reference points. They decide which metals can be extracted by carbon reduction and which metals react with dilute acids.
Which blast furnace equations do I need?
Carbon burning (C + O2 → CO2), carbon dioxide reduced to carbon monoxide (CO2 + C → 2CO), iron(III) oxide reduced by carbon monoxide (Fe2O3 + 3CO → 2Fe + 3CO2), and limestone decomposing then removing the silica impurity (CaCO3 → CaO + CO2, then CaO + SiO2 → CaSiO3, the slag).
Why is aluminium extracted by electrolysis but iron by carbon reduction?
Aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide. Iron is less reactive than carbon, so carbon (via carbon monoxide) reduces iron(III) oxide cheaply. Electrolysis is more expensive, so it is only used where it must be.
What is the difference between sacrificial protection and barrier protection?
Barrier methods (paint, grease, plastic coating) keep oxygen and water away from the iron. Protection stops the moment the barrier is scratched. Sacrificial protection attaches a more reactive metal such as zinc, which corrodes in preference to the iron and keeps protecting even when the surface is scratched.
How do I explain why alloys are harder than pure metals?
In a pure metal, layers of identical atoms slide over each other easily. In an alloy, atoms of different sizes disrupt the regular layers, so the layers can no longer slide. The scoring ideas are different-sized atoms and layers prevented from sliding.