Topic 10 Practice Paper: Chemistry of the environment — mark scheme (print)

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QQ/IGCSE-CHEM/T10

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

Mark scheme

Chemistry of the environment

Topic 10 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	DThe final 1% is mostly argon and the other noble gases, with a trace of carbon dioxide.	1
2	BSulfur compounds in the fuel burn to sulfur dioxide, the main cause of acid rain from power stations.	1
3	AOxygen is about 21%; nitrogen is about 78% and the noble gases with CO₂ share the rest.	1
4	CAquatic life breathes dissolved oxygen, which is why deoxygenation of water damages ecosystems.	1
5	DOnly an NPK blend contains all three essential elements; the salts listed supply nitrogen alone, and calcium carbonate is not a fertiliser.	1
6	AThe paper turns from blue to pink in water, but gives no information about purity — that needs boiling-point data.	1
7	BPure substances freeze at one sharp temperature; solidifying across a range shows the liquid is impure.	1
8	CSedimentation settles the large particles and filtration catches the rest; chlorination kills microbes and does not remove solids.	1
9	BAmmonium salts and nitrates are valued as fertilisers for their nitrogen content, which drives leafy growth.	1
10	DRotting plant material and the digestion of animals such as cattle release methane, a potent greenhouse gas.	1

Section B: Structured questions[20 marks]

Question	Answer and marking points	Marks
11(a)	Distillation removes the dissolved chemicals present in tap water, so distilled water has far fewer chemical impurities that could interfere with tests and reactions. distillation removes dissolved chemicals [1] so it will not interfere with experiments / tests [1]	2
11(b)	It is not pure: pure water boils at exactly 100 °C, and the raised boiling point shows dissolved impurities. not pure, because the boiling point differs from 100 °C [1]	1
11(c)	sedimentation and filtration [1]	1
11(d)	Passing the water through carbon. carbon treatment [1]	1
	Total for Question 11	5
12(a)	Nitrogen, phosphorus and potassium. nitrogen, phosphorus, potassium [1]	1
12(b)	Each harvest removes the mineral elements from the soil, so they must be replaced for the next crop to grow well. crops remove mineral elements from the soil [1] fertiliser replaces them / improves plant growth [1]	2
12(c)	Ammonium nitrate, NH₄NO₃. [1]	1
12(d)	Nitrates and phosphates cause deoxygenation of the water, damaging or killing aquatic life. deoxygenation / damage to aquatic life [1]	1
	Total for Question 12	5
13(a)	Carbon dioxide (power station and traffic) and methane (cattle). carbon dioxide and methane [1]	1
13(b)	They absorb the rising thermal energy, reflect some of it back towards the surface and re-emit it in all directions, so less thermal energy escapes to space. absorb / reflect thermal energy [1] less thermal energy escapes to space [1]	2
13(c)	Reduce the size of the cattle herds (less methane), and switch road vehicles to hydrogen or renewable electricity (less carbon dioxide). a valid farm strategy such as fewer cattle [1] a valid road strategy such as hydrogen or electric vehicles [1]	2
	Total for Question 13	5
14(a)	Nitrogen and oxygen; the very high temperature inside the engine supplies the energy for the reaction. nitrogen and oxygen [1] high temperature [1]	2
14(b)	2CO + 2NO → 2CO₂ + N₂ [1]	1
14(c)	Any two of: acid rain; photochemical smog; respiratory problems. two valid effects [1]	1
14(d)	Carbon monoxide (or particulates); carbon monoxide is toxic, particulates raise the risk of respiratory problems and some cancers. carbon monoxide or particulates with a matching effect [1]	1
	Total for Question 14	5

— End of mark scheme —