Metals, Alloys and Extraction: Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Metals and Extraction revision notes

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Questions

1. Place these metals in order of decreasing reactivity: iron, potassium, copper, zinc, calcium. [2]

2. Explain how the reactivity of a metal determines its method of extraction. [3]

3. Iron is extracted in the blast furnace.

(a) State the three raw materials added. [3] (b) Write the equation for the reduction of iron(III) oxide by carbon monoxide. [1] (c) Explain the purpose of the limestone, including an equation. [3]

4. Aluminium is extracted by electrolysis rather than by reduction with carbon.

(a) Explain why. [2] (b) Write the half-equation at the cathode. [1] (c) Explain why cryolite is added. [2] (d) Explain why the anodes must be replaced regularly. [2]

5. Explain, in terms of structure, why an alloy is harder than the pure metal. [3]

6. (Extension beyond this resource’s core scope — rusting and corrosion protection are covered in Metal Properties and Reactivity .) Rusting requires two substances.

(a) Name them. [2] (b) Describe how galvanising protects iron, and explain why it still works if the coating is scratched. [3]

7. Name the two metals that make up brass, and the metals and non-metal that make up stainless steel. [3]

8. State one property of aluminium that makes it suitable for overhead electrical cables, and explain why aluminium is used rather than copper despite copper being a better conductor. [3]

9. For each of the following metals, state whether it would be extracted by electrolysis, by reduction with carbon, or by neither method, and give a reason in each case: (a) potassium (b) zinc (c) gold. [6]

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Answers

1. potassium > calcium > zinc > iron > copper [1] [1].

2. Metals more reactive than carbon must be extracted by electrolysis [1]. Metals less reactive than carbon can be extracted by reduction with carbon, which is cheaper [1]. Very unreactive metals such as gold occur native and need no extraction [1].

3. (a) Iron ore (haematite), coke, limestone [1] [1] [1] (hot air also accepted). (b) Fe₂O₃ + 3CO → 2Fe + 3CO₂ [1]. (c) It removes acidic impurities, mainly silicon dioxide [1]. It first decomposes: CaCO₃ → CaO + CO₂ [1], then CaO + SiO₂ → CaSiO₃ (slag) [1].

4. (a) Aluminium is more reactive than carbon [1], so carbon cannot reduce its oxide [1]. (b) Al³⁺ + 3e⁻ → Al [1]. (c) It lowers the melting point of the aluminium oxide [1], reducing the energy required and hence the cost [1]. (d) Oxygen is produced at the anode [1] and reacts with the carbon anodes at high temperature, burning them away as carbon dioxide [1].

5. An alloy contains atoms of different sizes [1], which disrupt the regular layers of the pure metal [1], so the layers cannot slide over one another as easily [1].

6. (a) Water [1] and oxygen [1]. (b) The iron is coated with zinc, which forms a barrier excluding oxygen and water [1]. Zinc is more reactive than iron, so where the coating is scratched and the iron is exposed, the zinc is oxidised in preference — sacrificial protection — so the iron is still protected [1]; this sacrificial protection is why galvanising continues to work even once the barrier is broken [1].

7. Brass is copper and zinc [1]. Stainless steel is iron [1], with chromium, nickel and carbon [1].

8. Aluminium has a low density [1], and combined with good electrical conductivity this suits it to overhead cables [1]. Although copper conducts electricity better, aluminium’s much lower density makes the cables far lighter for a given length, reducing the load on supporting pylons and the overall cost, which outweighs copper’s conductivity advantage for this specific use [1].

9. (a) Electrolysis [1]. Potassium is above carbon in the reactivity series, so carbon is not a strong enough reducing agent to displace it from its compound [1]. (b) Reduction with carbon [1]. Zinc is below carbon in the reactivity series, so carbon can displace it, and this is cheaper than electrolysis [1]. (c) Neither — gold is found native (uncombined) in the Earth’s crust [1], because it is so unreactive that it does not readily form compounds with other elements, so no chemical extraction is needed [1].

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Where marks are usually lost

• Giving carbon reduction for a metal above carbon in the reactivity series.
• Not giving both equations for the role of limestone.
• Saying cryolite acts as a catalyst — it lowers the melting point.
• Explaining alloy hardness without mentioning disrupted layers.
• Naming a metal’s use without pairing it with the specific property that explains it — “aluminium is used in aircraft” alone earns no credit without “because of its low density.”
• Forgetting the non-metal (carbon) when naming stainless steel’s full composition.
• Assuming the better conductor is always chosen for an electrical application, without weighing other properties such as density or cost against conductivity.

Uses linked to properties — the pairing to remember

Metal	Use	Property that explains it
Aluminium	Aircraft manufacture	Low density
Aluminium	Overhead electrical cables	Low density + good conductivity
Aluminium	Food containers	Resistance to corrosion (oxide layer)
Copper	Electrical wiring	Excellent conductivity + ductility
Iron/steel	Construction, vehicles	Strength, low cost
Zinc	Galvanising	More reactive than iron

For condensed recall notes on this topic, see the Metals and Extraction revision notes; for the full explanation with additional detail, see the Metals, Alloys and Extraction study guide.