5 (a) Petroleum is a mixture of hydrocarbons. Useful products are obtained by process X and process Y, as shown in Fig. 5.1. petroleum strong heat alkenes gasoline process X process Y naphtha naphtha Fig. 5.1 (i) Process X separates gasoline and naphtha from petroleum. Name process X. … [1] (ii) Process Y produces alkenes. Name process Y. … [1] (iii) State whether process Y is a chemical change or a physical change. Explain your answer. change … explanation … … [1] (iv) Describe a chemical test for alkenes, and state the observation for a positive result. test … result … [2] (b) The structure of a molecule of propene, an alkene, is shown in Fig. 5.2. C H C C H H H H H Fig. 5.2 Water is formed during the complete combustion of propene. (i) Identify the other substance that is formed during this combustion. … [1] (ii) Name the gas in air that reacts with propene during combustion, and state the percentage of this gas in clean air. gas … percentage … [1] (iii) Use Fig. 5.2 to deduce the formula of propene. … [1] [Total: 8]

5(a)(i) fractional distillation ; 1 5(a)(ii) cracking ; 1 5(a)(iii) change: chemical AND explanation: new substances are made / bonds are broken / new bonds are formed ; 1 5(a)(iv) test: (add aqueous) bromine ; result: (orange to) colourless / decolourises ; 2 5(b)(i) carbon dioxide / CO2 ; 1 5(b)(ii) gas: oxygen AND percentage: 21(%) ; 1 5(b)(iii) C3H6 ; 1

5 (a) Copper is extracted from copper(II) oxide by heating with carbon. (i) Complete the word equation for this reaction. copper + + [2] (ii) Copper(II) oxide is reduced to copper in this reaction. Explain what is meant by the term reduced. … … [1] (b) Brass is a mixture of copper and zinc. (i) State the name of this type of mixture. … [1] (ii) Door keys are sometimes made from brass. Suggest why brass, rather than pure copper, is used to make door keys. … … [1] (c) Aluminium is extracted from aluminium oxide. (i) The ratio of aluminium atoms to oxygen atoms in aluminium oxide is shown. Al : O 1 : 1.5 Deduce the formula of aluminium oxide. … [1] (ii) State the method used to extract aluminium from aluminium oxide. … [1] (iii) Suggest why carbon cannot be used to extract aluminium from aluminium oxide. Use ideas about reactivity in your answer. … … [1] (d) Copper is a transition element. Aluminium is not a transition element. (i) Suggest one property of copper that is not shown by aluminium. … [1] (ii) Suggest one physical property that is shown by both copper and aluminium. … [1] [Total: 10]

5(a)(i) copper oxide + carbon → copper + carbon dioxide LHS correct (either order) ; RHS correct ; 2 5(a)(ii) loss of oxygen (from copper oxide) ; 1 5(b)(i) alloy ; 1 5(b)(ii) brass is, hard-wearing / harder / stronger / corrosion resistant ; 1 5(c)(i) Al2O3 ; 1 5(c)(ii) electrolysis ; 1 5(c)(iii) carbon is less reactive (than aluminium) / aluminium is more reactive (than either carbon or copper) ; 1 5(d)(i) (copper) forms coloured compounds / catalytic activity / higher density / higher melting point ; 1 5(d)(ii) (electrical / heat / thermal) conductor / malleable / ductile ; 1

8 (a) An atom of lead is represented by the symbol shown. 207 82 Pb (i) Deduce the number of electrons and number of neutrons in this atom. electrons … neutrons … [2] (ii) The proton number (atomic number) of lead is 82. Define the term proton number. … … [1] (iii) State the charges of protons, neutrons and electrons. protons … neutrons … electrons … [1] (b) Lead is extracted from molten lead(II) bromide using the apparatus shown in Fig. 8.1. molten lead(II) bromide – + low voltage d.c. supply Fig. 8.1 (i) Name the process shown in Fig. 8.1. … [1] (ii) State the name of the electrode at which lead forms. … [1] (c) Lead is extracted from lead(II) oxide, PbO, by heating with carbon. Carbon dioxide is also made in this endothermic reaction. (i) Describe what is meant by an endothermic reaction. … … [1] (ii) Complete the word equation for this reaction. lead + + [1] (iii) Circle the word to show whether lead(II) oxide is oxidised or reduced in this reaction. Explain your answer. oxidised reduced explanation … … [1] (d) A teacher has a different compound of lead. When this compound of lead reacts with dilute hydrochloric acid, carbon dioxide is formed. Suggest the name of this compound of lead. … [1] [Total: 10]

8(a)(i) (electrons) 82 ; (neutrons) 125 ; 2 8(a)(ii) the number of protons in the nucleus of an atom ; 1 8(a)(iii) (protons) +1 (neutrons) no charge (electrons) -1 ; all three needed for one mark 1 8(b)(i) electrolysis ; 1 8(b)(ii) cathode ; 1 8(c)(i) takes in, heat / energy ; 1 8(c)(ii) ; 1 8(c)(iii) reduced (circled) AND (explanation) loses oxygen ; 1 8(d) lead carbonate / PbCO3 ; 1 To earn marks, you must correctly state 82 electrons and 125 neutrons. You need to define proton number as the number of protons in the nucleus of an atom. For charges, you must state +1 for protons, no charge for neutrons, and -1 for electrons, with all three correct for the mark. You must name the process as 'electrolysis' and the electrode where lead forms as the 'cathode'. For the reaction with carbon, you need to state that it 'takes in heat/energy', draw the correct energy profile diagram, and explain that lead(II) oxide is 'reduced' because it 'loses oxygen'. Finally, you must name 'lead carbonate' or 'PbCO3' as the compound that causes acid rain.

8 (a) A student reacts a piece of magnesium with dilute hydrochloric acid, as shown in Fig. 8.1. A funnel holds the magnesium under a measuring cylinder to collect the gas formed. gas magnesium measuring cylinder dilute hydrochloric acid funnel Fig. 8.1 (i) State one other piece of apparatus that the student needs to use to determine the rate of this reaction. … [1] (ii) Suggest one change that increases the rate of this reaction. … [1] (iii) The student repeats the experiment under the same conditions, using the same mass of zinc instead of magnesium. State and explain the effect of this change on the rate of reaction. effect … explanation … [1] (b) Brass is a mixture of zinc and copper. (i) State the general name of mixtures such as brass that contain different metals. … [1] (ii) Suggest why brass, and not pure copper, is used to make coins. … … [1] (c) Some copper compounds are used as catalysts. Name the collection of metals in the Periodic Table that includes copper. … [1] (d) Copper is extracted from copper oxide using carbon. (i) Describe one condition needed for this process. … [1] (ii) State and explain whether copper is oxidised or reduced in this process. copper is … explanation … … [1] [Total: 8]

8(a)(i) stop-clock ; 1 8(a)(ii) any one from: increase temperature ; increase concentration (of acid) ; increase surface area (of Mg) / use Mg powder / use smaller pieces ; add a catalyst ; 1 8(a)(iii) effect: decrease / slower (rate) AND explanation: zinc is less reactive (than magnesium) ORA ; 1 8(b)(i) alloy ; 1 8(b)(ii) brass is, stronger / harder / less malleable / hardwearing / durable / corrodes or oxidises less / doesn’t go green ; 1 8(c) transition (elements / metals) ; 1 8(d)(i) high temperature ; 1 8(d)(ii) copper is: reduced AND explanation: (copper) loses, oxygen / O ; 1

Cambridge IGCSE Combined Science · 0653

IGCSE Combined Science (0653) Chemical reactions past paper questions

Revise IGCSE Combined Science (0653) — Chemical reactions with real Cambridge past-paper questions grouped by topic, each shown with its marking scheme. Working one topic at a time targets exactly the skill each question tests.

261 free questions from 2016–2021, each with its marking scheme. Open the full topical bank to filter by subtopic, paper, and year.

Chemical reactions in IGCSE Combined Science 0653 exams, 2020–2025

Across 2020–2025, Chemical reactions accounted for 269 questions worth 1,144 marks in Cambridge IGCSE Combined Science (0653) papers.

By year
Year	Questions	Marks
2020	35	182
2021	50	187
2022	52	219
2023	47	209
2024	52	217
2025	33	130

Most-tested subtopics

C6.2 Rate of reaction543 marks
C6.3 Redox272 marks
C6.1 Physical and chemical changes239 marks

Appears in

Paper 1 · 77 qs
Paper 2 · 87 qs
Paper 3 · 43 qs
Paper 4 · 28 qs
Paper 5 · 14 qs
Paper 6 · 20 qs

All most-tested Combined Science topics

2021 May/Jun · Paper 3 · Q5 · 8 marks
Marking scheme
$Mark scheme: 5(a)(i) fractional distillation ; 1 5(a)(ii) cracking ; 1 5(a)(iii) change: chemical AND explanation: new substances are…$ Get Steven’s plain-English explanation
2021 May/Jun · Paper 3 · Q5 · 10 marks
Marking scheme
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2021 Feb/Mar · Paper 3 · Q8 · 10 marks
Marking scheme
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2021 May/Jun · Paper 3 · Q8 · 8 marks
Marking scheme
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2021 May/Jun · Paper 1 · Q14 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q14
Answer: B
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