IGCSE Chemistry: Metals Practice Questions
Metals are arranged in a reactivity series based on their tendency to lose electrons and form positive ions. The method used to extract a metal from its ore depends on its position: reactive metals are extracted by electrolysis and less reactive ones by reduction with carbon.
Topic 9 of Cambridge IGCSE Chemistry 0620 combines the reactivity series with two industrial processes and a corrosion topic. The blast furnace equations and the explanation of why alloys are harder are the two questions that recur most. The questions below cover both.
What you need to know for Metals
- Reactivity seriesPotassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold. Carbon and hydrogen are included as reference points for extraction and displacement.
- Choosing an extraction methodMetals above carbon in the series are extracted by electrolysis of the molten ore. Metals below carbon can be extracted by reduction with carbon, which is cheaper.
- Blast furnaceCoke burns to form carbon dioxide, which reacts with more coke to form carbon monoxide. Carbon monoxide reduces iron(III) oxide to iron. Limestone decomposes to calcium oxide, which removes silicon dioxide impurities as slag.
- RustingIron rusts only when both water and oxygen are present. Salt increases the rate. Prevention works by barrier methods such as painting, greasing and plastic coating, or by sacrificial protection.
- Sacrificial protectionA more reactive metal such as zinc or magnesium is attached to the iron. The more reactive metal loses electrons in preference, so it corrodes instead of the iron.
- AlloysA mixture of a metal with other elements. Alloys are harder than pure metals because the different sized atoms disrupt the regular layers, so the layers cannot slide over one another easily.
IGCSE Chemistry Metals questions and answers
4 exam-style questions written to the 0620 syllabus. Try each one on paper first, then open the worked answer to check your method against the marks.
Write equations for the three main reactions that occur in the blast furnace during the extraction of iron, and state the purpose of the limestone.
Show the worked answer
- Coke burns in the hot air blast: C + O2 gives CO2. This reaction is exothermic and supplies the heat for the furnace.
- Carbon dioxide reacts with more hot coke higher up the furnace: CO2 + C gives 2CO.
- Carbon monoxide is the reducing agent: Fe2O3 + 3CO gives 2Fe + 3CO2. Molten iron runs to the bottom of the furnace.
- Limestone, calcium carbonate, decomposes in the heat: CaCO3 gives CaO + CO2.
- The calcium oxide produced is basic and reacts with the acidic silicon dioxide impurity in the ore to form calcium silicate, the molten slag, which floats on the iron and is run off separately.
Explain, in terms of structure, why brass is harder than pure copper.
Show the worked answer
- In a pure metal such as copper, the atoms are all the same size and are arranged in regular layers.
- When a force is applied, these layers can slide over one another, which is why pure metals are relatively soft and malleable.
- Brass is an alloy of copper and zinc, and zinc atoms are a different size from copper atoms.
- The differently sized atoms disrupt the regular arrangement of the layers, so the layers can no longer slide over one another easily. The alloy is therefore harder and stronger than the pure metal.
A student sets up three test tubes containing iron nails. Tube A has water and air, tube B has boiled water with a layer of oil on top, and tube C has dry air with a drying agent. Only the nail in tube A rusts. Explain what this shows.
Show the worked answer
- Tube A contains both water and oxygen from the air, and the nail rusts.
- Tube B contains water, but boiling removes the dissolved oxygen and the oil layer stops more from dissolving. No oxygen means no rusting, so oxygen is necessary.
- Tube C contains air but the drying agent removes water vapour. No water means no rusting, so water is necessary.
- Since rusting occurs only when both are present, the experiment shows that iron requires both water and oxygen to rust.
Blocks of zinc are attached to the steel hull of a ship. Explain how this prevents the hull from rusting.
Show the worked answer
- Zinc is above iron in the reactivity series, so it loses electrons more readily than iron does.
- When both metals are in contact in seawater, the zinc is oxidised in preference to the iron, forming Zn2+ ions.
- The electrons released pass to the iron, so the iron does not lose electrons and does not corrode.
- The zinc is gradually used up and must be replaced periodically. This is sacrificial protection.
Common mistakes in this topic
- Saying carbon reduces iron oxide in the blast furnace rather than carbon monoxide.
- Forgetting that limestone removes acidic impurities, and confusing slag with the molten iron.
- Claiming aluminium does not corrode. It reacts quickly with oxygen, but forms a tough oxide layer that protects the metal underneath.
- Saying alloys are harder because the atoms are bonded more strongly.
- Describing rusting as a reaction with air alone. It needs both water and oxygen.
Exam tips
- Learn the reactivity series with carbon and hydrogen in place. Their positions decide the extraction method and displacement outcomes.
- For the blast furnace, learn four equations in order and state which one supplies the heat.
- For alloy questions, always describe layers sliding. That is the mechanism examiners want.
- In rusting experiments, name what each control tube removes and what that proves.
- Distinguish barrier methods from sacrificial protection and give one example of each.
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Metals FAQs
Why is aluminium extracted by electrolysis but iron by reduction with carbon?
Aluminium is above carbon in the reactivity series, so carbon cannot remove oxygen from aluminium oxide. Electrolysis of the molten ore is required. Iron is below carbon, so carbon monoxide produced from coke can reduce iron oxide, which is far cheaper than electrolysis.
What conditions are needed for iron to rust?
Both water and oxygen must be present. Removing either one prevents rusting, which is why boiling water to remove dissolved oxygen or using a drying agent both stop the process. Dissolved salt speeds rusting up considerably, which is why cars in coastal areas corrode faster.
Why are alloys harder than pure metals?
In a pure metal all the atoms are the same size and arranged in regular layers that can slide over one another when a force is applied. An alloy contains atoms of a different size, which disrupt the regular layers so they cannot slide easily. The alloy is therefore harder and stronger.
What is sacrificial protection?
A more reactive metal, usually zinc or magnesium, is attached to iron or steel. Because it loses electrons more readily than iron, it is oxidised in preference and corrodes instead of the iron. The sacrificial metal is gradually used up and must be replaced.
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Written to the published Cambridge IGCSE Chemistry (0620) syllabus. Check your school entry code and syllabus year, because Core and Extended candidates are assessed on different content. Last reviewed 2026-08-12.