Topic 9 Practice Paper: Metals — mark scheme (print)

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QQ/IGCSE-CHEM/T9

IGCSE · Cambridge IGCSE Chemistry (Extended (Core + Supplement))

Mark scheme

Metals

Topic 9 Practice Paper · Maximum mark: 30

Notes for markers

Award one mark for each point marked [1], up to the marks shown for the part.
Accept answers worded differently that show the same understanding.
Units are required where the answer line shows one. ecf: allow an error carried forward.

Section A: Multiple-choice questions[10 marks]

Question	Answer
1	CMagnesium is the highest of the four in the reactivity series, so it loses electrons most readily and reacts fastest with the acid.	1
2	AGold is so unreactive that it exists as the free metal; reactive metals are always locked in compounds.	1
3	DLimestone decomposes to calcium oxide, which combines with silicon dioxide to form molten calcium silicate slag.	1
4	BMagnesium lies above carbon in the reactivity series, so carbon cannot displace it; zinc, iron and copper all sit below carbon.	1
5	ABrass is copper plus zinc. Copper plus tin gives bronze, and iron with chromium, nickel and carbon gives stainless steel.	1
6	CA low density keeps the aircraft light, while the metal still provides enough strength for an airframe.	1
7	DOnly the fourth nail has both oxygen and water together, and rusting needs both.	1
8	BGalvanising is a zinc coating, which both blocks air and moisture and protects sacrificially where the coating is scratched.	1
9	CPositive Al³⁺ ions move to the negative cathode and each gains three electrons to form aluminium atoms.	1
10	DCopper sits below hydrogen, so it is unreactive to water and acids, and its conductivity and ductility suit it to wiring.	1

Section B: Structured questions[20 marks]

Question	Answer and marking points	Marks
11(a)	R is the most reactive: it reacts with cold water, which only metals above magnesium in the series can do, while P needs acid and Q does not react at all. R identified [1] reacting with cold water implies very high reactivity compared with the other observations [1]	2
11(b)	Copper — it is the only one of the three below hydrogen, so it does not react with dilute acid. copper, because it is below hydrogen in the series [1]	1
11(c)	Q, then P, then R. Q < P < R [1]	1
11(d)	Hydrogen; a lighted splint held at the mouth of the tube gives a squeaky pop. hydrogen with the pop test [1]	1
	Total for Question 11	5
12(a)	The alloy contains atoms of different sizes that disturb the regular lattice, so the layers of atoms cannot slide past one another easily; the harder material keeps its edge. different-sized atoms distort the layers [1] layers can no longer slide, so it is harder [1]	2
12(b)	Stainless steel, containing iron with chromium, nickel and carbon. stainless steel [1] chromium, nickel and carbon [1]	2
12(c)	Stainless steel is hard and resists corrosion (rusting), so it survives inside the body without degrading. hard and corrosion-resistant [1]	1
	Total for Question 12	5
13(a)	Tube C only. [1]	1
13(b)	Tube A has oxygen but no water and no rust forms; tube B has water but no oxygen and no rust forms. So rusting needs both oxygen and water together. A lacks water, B lacks oxygen, neither rusts [1] therefore both oxygen and water are required [1]	2
13(c)	Magnesium is more reactive than iron, so it loses electrons preferentially and corrodes instead of the nail — sacrificial protection. magnesium is more reactive / loses electrons first [1] therefore the iron is protected sacrificially [1]	2
	Total for Question 13	5
14(a)	Reduction by heating with carbon (or carbon monoxide). heating with carbon / carbon monoxide reduction [1]	1
14(b)	Aluminium is above carbon in the reactivity series, so carbon cannot displace it from its oxide. aluminium more reactive than carbon [1]	1
14(c)	ZnO + C → Zn + CO (or 2ZnO + C → 2Zn + CO₂). balanced equation for zinc oxide reduced to zinc [1]	1
14(d)	Aluminium is extracted by electrolysis, which consumes very large amounts of electricity; recycling aluminium avoids repeating that energy-hungry process, whereas iron extraction by carbon reduction is cheaper to repeat. aluminium extraction is electrolysis, which is very energy-intensive [1] recycling avoids the re-extraction cost / uses only a small fraction of the energy [1]	2
	Total for Question 14	5

— End of mark scheme —