Cambridge IGCSE Chemistry 9 Metals Exam Questions

About Cambridge IGCSE Chemistry 9 Metals

Metals in Cambridge IGCSE Chemistry 0620 covers the physical and chemical properties of metals, their uses, alloys, the reactivity series, corrosion and extraction. You need to explain why alloys are harder than pure metals, place metals in order of reactivity from their reactions with water, steam and dilute acid, and describe how iron is extracted in the blast furnace. Extended candidates also explain sacrificial protection and the extraction of aluminium by electrolysis. The topic links to metallic bonding, redox and electrolysis. Examiners regularly test blast furnace equations, the conditions needed for rusting, displacement reactions and matching a metal's use to a specific property.

What you need to know

• 9.1 Properties Metals are good conductors of heat and electricity, malleable, ductile and usually have high melting and boiling points. They react with dilute acids, cold water or steam, and oxygen, depending on their reactivity.
• 9.2 Uses Aluminium is used in aircraft because of its low density and in food containers because it resists corrosion. Copper is used in electrical wiring because it is a good conductor and ductile.
• 9.3 Alloys An alloy is a mixture of a metal with other elements, e.g. brass (copper and zinc) and stainless steel (iron with chromium, nickel and carbon). Alloys are harder and stronger because different sized atoms disrupt the layers, so they slide less easily.
• 9.4 Reactivity series Potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold. A more reactive metal displaces a less reactive metal from its compounds. Extended candidates explain aluminium's apparent unreactivity by its protective oxide layer.
• 9.5 Corrosion Iron rusts when it is in contact with both water and oxygen, forming hydrated iron(III) oxide. Barrier methods include painting, greasing and coating with plastic. Galvanising coats iron with zinc; Extended candidates explain sacrificial protection, where zinc is oxidised in preference to iron.
• 9.6 Blast furnace Haematite, coke and limestone are added. C + O2 → CO2; CO2 + C → 2CO; Fe2O3 + 3CO → 2Fe + 3CO2. Limestone decomposes to calcium oxide, which reacts with silicon dioxide impurities to form slag: CaO + SiO2 → CaSiO3.
• 9.6 Aluminium and zinc (Supplement) Aluminium is extracted from bauxite by electrolysis of aluminium oxide dissolved in molten cryolite, with carbon electrodes; the anodes burn away as oxygen reacts with them. Zinc is extracted from zinc blende (zinc sulfide) via zinc oxide, which is reduced by carbon.

Common mistakes in 9 Metals

• Saying rusting needs only air or only water. Both oxygen and water must be present.
• Explaining alloy hardness as the alloy being more strongly bonded. The key point is that different sized atoms disrupt the regular layers so they cannot slide easily.
• Saying carbon reduces iron(III) oxide directly in the blast furnace. The main reducing agent is carbon monoxide.
• Explaining sacrificial protection as zinc forming a barrier only. Zinc is more reactive, so it loses electrons and corrodes instead of iron, even if the coating is scratched.
• Saying aluminium is extracted with carbon. Aluminium is more reactive than carbon, so electrolysis is needed.

Try three 9 Metals exam-style questions