1 Choose from the following compounds to answer the questions. C C H H3C H3C CH3 CH3 CH3 CH3 H2C H3C H3C H2C CH2 CH2 C O C H H H H H H A O C C H H O H F D C O C H O O CH3 C O C H H H C CH3 G O H2N C O C H CH3 H H H H H H C H3C C H E B Each compound may be used once, more than once or not at all. (a) State which compound: (i) has a molecule with only 11 atoms … [1] (ii) is oxidised to form ethanoic acid … [1] (iii) is an isomer of butene … [1] (iv) reacts with hydrogen in the presence of a catalyst to make an alkane … [1] (v) contains four different elements chemically combined. … [1] (b) Identify two compounds that have a pH of less than 7 in aqueous solution. … [1] [Total: 6]

1(a)(i) C 1 1(a)(ii) A 1 1(a)(iii) B 1 1(a)(iv) D 1 1(a)(v) H 1 1(b) C and F 1 To earn marks, you must correctly identify the specific compound (A, B, C, D, E, F, G, H) that matches each description, and for part (b), identify both compounds C and F.

1 Choose from the following oxides to answer the questions. aluminium oxide calcium oxide iron(II) oxide magnesium oxide silicon dioxide sodium oxide sulfur dioxide Each oxide may be used once, more than once or not at all. State which oxide: (a) has a simple molecular structure … [1] (b) is a coloured solid … [1] (c) contains ions with a 3+ charge … [1] (d) is a product of the thermal decomposition of calcium carbonate … [1] (e) contributes to acid rain. … [1] [Total: 5]

1(a) sulfur dioxide 1 1(b) iron(II) oxide 1 1(c) aluminium oxide 1 1(d) calcium oxide 1 1(e) sulfur dioxide 1 (a) To earn the mark, you must correctly identify sulfur dioxide as the oxide with a simple molecular structure. (b) To earn the mark, you must correctly identify iron(II) oxide as the coloured solid. (c) To earn the mark, you must correctly identify aluminium oxide as the oxide containing ions with a 3+ charge. (d) To earn the mark, you must correctly identify calcium oxide as the product of the thermal decomposition of calcium carbonate. (e) To earn the mark, you must correctly identify sulfur dioxide as the oxide that contributes to acid rain.

2 Helium, neon, argon, krypton, xenon and radon are noble gases in Group VIII. (a) Name the noble gas which has the greatest volume composition in air. … [1] (b) State one use for helium. … [1] (c) Radon is very unreactive. Use the electronic structure of radon to explain why. … … [1] (d) Two isotopes of radon are shown. 220 86Rn 222 86Rn (i) Give one similarity in the atomic structure of these two isotopes. … [1] (ii) Give one difference in the atomic structure of these two isotopes. … [1] (e) Xenon forms a compound that contains only xenon, oxygen and fluorine. The compound contains 22.1% oxygen by mass and 17.5% fluorine by mass. Calculate the empirical formula of this compound. empirical formula … [3] (f) A sample of neon has a volume of 21 dm3 at room temperature and pressure. (i) The temperature of the sample is increased. The pressure remains constant. Describe and explain, using kinetic particle theory, what happens to the volume of the sample. … … [1] (ii) The pressure of the sample is increased. The temperature remains constant. Describe and explain, using kinetic particle theory, what happens to the volume of the sample. … … [1] (iii) Calculate the mass of neon in the 21 dm3 sample. Give your answer to two significant figures. mass … g [2] [Total: 12]

2(a) argon 1 2(b) (air) balloons / undersea breathing apparatus 1 2(c) outer shell has 8 electrons 1 2(d)(i) 86 protons / 86 electrons / same electronic structure 1 2(d)(ii) radon-222 has two more neutrons / radon-220 has two fewer neutrons / radon-220 has 134 neutrons and radon-222 has 136 neutrons 1 2(e) percentage of xenon = 60.4 (1) mole ratio Xe : O : F is 60.4 / 130 : 22.1 / 16 : 17.5 / 19 OR 0.46 : 1.38 : 0.92 (1) empirical formula XeO3F2 (1) 3 2(f)(i) volume increases AND particles move faster / particles spread out more / particles move further apart 1 2(f)(ii) volume decreases AND particles move closer together / distance between particles decreases 1 2(f)(iii) moles = 21 / 24 OR 0.875 (1) mass = 18 (g) (1) 2 To earn marks, you must correctly name argon, state a valid use for helium, explain radon's unreactivity by mentioning its full outer electron shell, identify a similarity (protons/electrons/electronic structure) and a difference (number of neutrons) between the isotopes, and correctly calculate the empirical formula by showing the percentage of xenon, the mole ratios, and the final formula. For parts (f)(i) and (f)(ii), you need to state the change in volume and explain it in terms of particle movement. For (f)(iii), you must correctly calculate the moles and then the mass.

2 Oxygen, sulfur, selenium, tellurium and polonium are in Group VI. (a) State the percentage composition by volume of oxygen in dry air. … [1] (b) State one large-scale use for oxygen. … [1] (c) Two isotopes of polonium are shown. 20 8 9 4Po 21 8 0 4Po (i) Explain why both isotopes have the same chemical properties. … [1] (ii) Give one difference in the atomic structure of these two isotopes. … [1] (d) Selenium forms a compound that contains only selenium, oxygen and chlorine. The compound contains 9.6% oxygen by mass and 42.8% chlorine by mass. Calculate the empirical formula of this compound. empirical formula … [3] (e) A sample of oxygen has a volume of 11.5 dm3 at room temperature and pressure. (i) The temperature of the sample is decreased. The pressure remains constant. Describe and explain, using kinetic particle theory, what happens to the volume of the sample. … … [1] (ii) The pressure of the sample is decreased. The temperature remains constant. Describe and explain, using kinetic particle theory, what happens to the volume of the sample. … … [1] (iii) Calculate the mass of oxygen in the 11.5 dm3 sample at room temperature and pressure. Give your answer to two significant figures. mass … g [2] [Total: 11]

2(a) 21 (%) 1 2(b) steel making / welding / cutting metals / oxygen tents in hospitals / breathing apparatus / fuel cells 1 2(c)(i) same electronic structure / same electronic configuration 1 2(c)(ii) polonium-210 has one more neutron / polonium-209 has one less neutron / polonium-209 has 125 neutrons and polonium- 210 has 126 neutrons 1 2(d) percentage of selenium = 47.6 (1) mole ratio Se : O : Cl is 47.6 / 79 : 9.6 / 16 : 42.8 / 35.5 OR 0.60 : 0.60 : 1.21 (1) empirical formula SeOCl 2 (1) 3 2(e)(i) volume decreases AND particles move slower / particles less spread out / particles closer together 1 2(e)(ii) volume increases AND particles move further apart / particles more spread out / distance between particles increases 1 2(e)(iii) mol = 11.5 / 24 OR 0.479(117) (1) mass = 15 (g) (1) 2 To earn marks, you must provide the correct percentage for oxygen in air, state a valid large-scale use for oxygen, explain that isotopes have the same chemical properties due to identical electronic structures, and identify the difference in neutron count between the given isotopes. For the empirical formula calculation, you need to correctly calculate the percentage of selenium, determine the mole ratios, and then state the correct empirical formula. For part (e)(i), you must state that the volume decreases and explain this using kinetic particle theory by mentioning particles moving slower or being closer together. For part (e)(ii), you must state that the volume increases and explain this by mentioning particles moving further apart or being more spread out. For part (e)(iii), you must correctly calculate the moles of oxygen and then use this to find the mass.

Cambridge O Level Chemistry · 5070

O-Level Chemistry (5070) Atoms, elements and compounds past paper questions

Revise O-Level Chemistry (5070) — Atoms, elements and compounds 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.

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

Atoms, elements and compounds in O-Level Chemistry 5070 exams, 2020–2025

Across 2020–2025, Atoms, elements and compounds accounted for 237 questions worth 924 marks in Cambridge O Level Chemistry (5070) papers.

By year
Year	Questions	Marks
2020	45	200
2021	34	156
2022	43	160
2023	35	141
2024	38	128
2025	42	139

Most-tested subtopics

2.5 Simple molecules and covalent bonds331 marks
2.4 Ions and ionic bonds304 marks
2.2 Atomic structure and the Periodic Table175 marks

Appears in

Paper 1 · 150 qs
Paper 2 · 85 qs
Paper 4 · 2 qs

All most-tested Chemistry topics

2021 May/Jun · Paper 2 · Q1 · 6 marks
Marking scheme
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2021 Oct/Nov · Paper 2 · Q1 · 5 marks
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2021 May/Jun · Paper 2 · Q2 · 12 marks
Marking scheme
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2021 May/Jun · Paper 2 · Q2 · 11 marks
Marking scheme
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2021 May/Jun · Paper 1 · Q6 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q6
Answer: C
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