6 The diagram shows part of the structures of sodium bromide and graphite at room temperature and pressure. Na+ Br – Na+ Br – Na+ Br – Na+ Br – Br – Na+ Na+ Br – (a) Describe the physical properties of these substances in terms of: ● volatility sodium bromide … graphite … ● solubility in water sodium bromide … graphite … ● electrical conductivity when solid. sodium bromide … graphite … [5] (b) When dilute sulfuric acid is electrolysed using inert electrodes, oxygen gas is produced at the positive electrode. Name the gas produced at the negative electrode. … [1] (c) Aqueous sodium bromide reacts with aqueous chlorine. (i) Complete the word equation for this reaction. sodium bromide + chlorine → … … + … [2] (ii) Explain in terms of the reactivity of the halogens why aqueous sodium chloride does not react with aqueous bromine. … … [1] [Total: 9]

6(a) 5 of any of: volatility: • sodium bromide (very) low / does not evaporate (at room temperature) • graphite low / does not evaporate (at room temperature) solubility: • sodium bromide soluble / dissolves • graphite insoluble / does not dissolve electrical conductivity: • sodium bromide does not conduct • graphite conducts 5 6(b) hydrogen 1 6(c)(i) sodium chloride (1) bromine (1) 2 6(c)(ii) chlorine is more reactive than bromine / chlorine higher than bromine in reactivity series 1

6 The diagrams show part of the structures of potassium iodide and bromine at room temperature and pressure. K+ I– K+ I– K+ I– K+ I– I– K+ K+ I– Br Br Br Br Br Br Br Br Br Br Br Br Br Br Br Br (a) Describe the physical properties of these substances in terms of: ● volatility potassium iodide … bromine … ● solubility in water potassium iodide … bromine … ● electrical conductivity when molten (liquid). potassium iodide … bromine … [5] (b) Molten potassium iodide is electrolysed using carbon (graphite) electrodes. (i) Name the substance produced at the positive electrode. … [1] (ii) Aqueous potassium iodide reacts with aqueous bromine. Complete the word equation for this reaction. potassium iodide + bromine → … … + … [2] (iii) Explain in terms of the reactivity of the halogens why aqueous potassium chloride does not react with aqueous bromine. … … [1] (c) Name the change of state when liquid bromine changes to solid bromine. … [1] [Total: 10]

6(a) 1 mark each for any 5 of: volatility: • potassium iodide: (very) low / does not evaporate (at room temperature) • bromine: high / evaporates rapidly (at room temperature) solubility: • potassium iodide: soluble / dissolves • bromine: (slightly) soluble / dissolves (slightly) electrical conductivity: • potassium iodide: conducts • bromine: does not conduct / poor conductor 5 6(b)(i) iodine 1 6(b)(ii) potassium bromide (1) iodine (1) 2 6(b)(iii) chlorine more reactive than bromine / bromine less reactive than chlorine 1 6(c) freezing / solidification 1

6 The diagram shows part of the structures of sodium chloride and pentane at room temperature and pressure. represents pentane, CH3CH2CH2CH2CH3 Na+ Cl – Na+ Cl – Na+ Cl – Na+ Cl – Cl – Na+ Na+ Cl – (a) Describe the differences in the physical properties of these substances in terms of: ● volatility sodium chloride … pentane … ● solubility in water sodium chloride … pentane … ● electrical conductivity when molten (liquid). sodium chloride … pentane … [5] (b) Concentrated aqueous sodium chloride is electrolysed using carbon (graphite) electrodes. Name the gas produced at the positive electrode. … [1] (c) Pentane is a fuel. Under some conditions pentane forms carbon monoxide. (i) State the condition under which pentane forms carbon monoxide. … [1] (ii) State one adverse effect of carbon monoxide on health. … [1] [Total: 8]

6(a) 1 mark each for any 5 of: volatility: • sodium chloride: (very) low / does not evaporate (at room temperature) • pentane: high / evaporates rapidly (at room temperature) solubility: • sodium chloride: soluble / dissolves • pentane: insoluble / does not dissolve electrical conductivity: • sodium chloride: conducts • pentane: does not conduct / poor conductor 5 6(b) chlorine 1 6(c)(i) incomplete combustion / combustion in limited air / combustion in limited oxygen 1 6(c)(ii) poisonous / toxic 1 (a) You must describe the differences in volatility (sodium chloride: low/does not evaporate; pentane: high/evaporates rapidly), solubility in water (sodium chloride: soluble/dissolves; pentane: insoluble/does not dissolve), and electrical conductivity when molten (sodium chloride: conducts; pentane: does not conduct/poor conductor) for both substances. (b) You must name the gas produced at the positive electrode as chlorine. (c) (i) You must state that carbon monoxide is formed due to incomplete combustion or combustion in limited air/oxygen. (ii) You must state that carbon monoxide is poisonous or toxic.

7 Sodium is manufactured by electrolysis. (a) Explain why sodium is manufactured by electrolysis and not by reduction with carbon. … [1] (b) The diagram shows the equipment for the production of sodium. + – power supply sodium molten sodium chloride (i) The anode is inert. Suggest a suitable substance that can be used for the anode. … [1] (ii) Label the anode on the diagram. [1] (iii) Describe, by reference to the diagram, how you know that sodium is less dense than molten sodium chloride. … [1] (c) When concentrated aqueous sodium chloride is electrolysed, gases are produced at each electrode. State the names of the products and give the observations at each electrode. product at the negative electrode … observations at the negative electrode … … product at the positive electrode … observations at the positive electrode … … [4] (d) Give two ways in which the physical properties of sodium are different from the physical properties of transition elements. 1 … 2 … [2] (e) The symbol equation for the production of sodium hydride is shown. 2Na + H2 → 2NaH (i) Write a word equation for this reaction. … [1] (ii) Suggest why the hydrogen must be dry. … [1] (iii) Sodium hydride reduces iron(III) oxide to iron. Fe2O3 + 3NaH → 2Fe + 3NaOH Explain how this equation shows that iron(III) oxide is reduced. … [1] (f) State the colour observed in the flame test for sodium. … [1] [Total: 14]

7(a) sodium is too reactive / sodium is high in the electrochemical series / it takes too high a temperature to extract sodium using carbon 1 7(b)(i) graphite / platinum 1 7(b)(ii) ‘square’ in middle of diagram labelled anode 1 7(b)(iii) the sodium floats on top of the sodium chloride 1 7(c) negative electrode: hydrogen (1) bubbles / fizzing / colourless gas (1) positive electrode: chlorine (1) bubbles / fizzing / green gas / yellow-green gas (1) 4 7(d) 1 mark each for any 2 of: • sodium is soft / not strong / more malleable / more ductile • sodium has low density • sodium has (relatively) low melting point 2 7(e)(i) sodium + hydrogen → sodium hydride 1 7(e)(ii) so that sodium does not react with water / sodium reacts with water 7(e)(iii) the iron oxide has lost oxygen 1 7(f) yellow (1) 1

Cambridge IGCSE Chemistry · 0620

IGCSE Chemistry (0620) Electrochemistry past paper questions

These questions cover electrolysis, electrode products, and simple cells.

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

Electrochemistry in IGCSE Chemistry 0620 exams, 2020–2025

Across 2020–2025, Electrochemistry accounted for 279 questions worth 1,196 marks in Cambridge IGCSE Chemistry (0620) papers.

By year
Year	Questions	Marks
2020	43	207
2021	42	177
2022	41	172
2023	43	197
2024	59	244
2025	51	199

Most-tested subtopics

4.1 Electrolysis of molten compounds625 marks
4.2 Electrolysis of aqueous solutions361 marks
4.5 Ionic half-equations357 marks

Appears in

Paper 1 · 76 qs
Paper 2 · 117 qs
Paper 3 · 47 qs
Paper 4 · 34 qs
Paper 5 · 1 q
Paper 6 · 4 qs

All most-tested Chemistry topics

2021 Oct/Nov · Paper 3 · Q6 · 9 marks
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2021 Oct/Nov · Paper 3 · Q6 · 10 marks
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2021 Oct/Nov · Paper 3 · Q6 · 8 marks
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2021 Feb/Mar · Paper 3 · Q7 · 14 marks
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2021 May/Jun · Paper 1 · Q10 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q10
Answer: A
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