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CAIE A Level Chemistry 9701

Atoms, molecules and stoichiometry questions

Exam-style questions on Atoms, molecules and stoichiometry, ordered from foundation to challenge. Pick one, write your answer the way you would in the exam, and it comes back marked against the mark scheme, point by point.

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Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.

  1. Explain4 marksStandardA student adds an excess of aqueous sodium carbonate to an aqueous solution of copper(II) sulfate. A pale blue precipitate of copper(II) carbonate forms and the mixture becomes colourless. Explain how the ionic…
  2. Describe5 marksStandardMagnesium is in Group 2 of the Periodic Table and nitrogen is in Group 5. Describe, in terms of outer-shell electrons, how the charge on the nitride ion can be predicted from nitrogen's position in the Periodic Table…
  3. Compare5 marksStandardA sample of carbon contains 99% carbon-12 atoms and 1% carbon-13 atoms. Compare the relative isotopic mass of one carbon-13 atom with the relative atomic mass of carbon in this sample.
  4. Compare5 marksStandardNitrogen reacts with oxygen to form nitrogen monoxide. N2(g) + O2(g) → 2NO(g) In an experiment, 40 cm³ of nitrogen is mixed with 60 cm³ of oxygen and the mixture is sparked so that the reaction goes to completion. All…
  5. Explain4 marksStandardThe Avogadro constant, L, is 6.02 × 10^23\ mol^-1. One atom of carbon-12 has a mass of exactly 12 atomic mass units (u), where 1\ u = 1.66 × 10^-24\ g. Explain what is meant by one mole of carbon-12 atoms in terms of…
  6. Suggest4 marksStandardThe mole is sometimes described as a counting unit, in the same way as a dozen. A student writes: 'A mole is just a large number: one mole of any substance contains 6.02 × 10^23 particles.' Suggest two ways in which…
  7. Compare5 marksStandardA student reacts aqueous sodium carbonate with dilute nitric acid. Compare the full balanced equation with the ionic equation for this reaction. Give both equations with state symbols and identify any spectator ions.
  8. Compare5 marksStandardSodium chloride, NaCl, is ionic; sulfur dioxide, SO2, is covalent. Compare relative molecular mass and relative formula mass, explaining what each is based on and why relative formula mass is used for ionic compounds…
  9. Describe5 marksStandardThe mole is defined using the isotope carbon-12. Describe, with reference to carbon-12 and the Avogadro constant, what is meant by one mole of a substance.
  10. Suggest4 marksStandardThe Avogadro constant, L, is 6.02 × 10²³ mol⁻¹. A student has one mole of methane, CH4, and one mole of sulfur dioxide, SO2. The two samples contain the same number of molecules, but the sulfur dioxide has the greater…
  11. Compare5 marksStandardA sample contains 0.5 mol of oxygen gas, O2, and a separate sample contains 0.5 mol of helium gas, He. The Avogadro constant is 6.02 × 10^23 mathrmmol^-1. Compare the two samples in terms of the numbers of particles…
  12. Compare5 marksStandardThe mole is a unit of amount of substance defined using the Avogadro constant. Compare the number of atoms in one mole of helium gas, He, with the number of atoms in one mole of carbon dioxide gas, CO2. Use the…
  13. Compare5 marksStandardThe mole is an SI base unit. A ream of paper contains exactly 500 sheets and is also a counting unit. The Avogadro constant is 6.02 × 10^23 mol⁻¹. Compare the mole with the ream in terms of what each unit counts, and…
  14. Explain4 marksStandardSulfur has a relative atomic mass of 32.06. A sample of the element contains several isotopes, including sulfur-32 and sulfur-34. Elemental sulfur exists as molecules with the formula S8. Explain what is meant by each…
  15. Suggest4 marksStandardBenzene can be represented by the empirical formula CH and the molecular formula C6H6. Suggest what is meant by the terms empirical formula and molecular formula, and suggest why the empirical formula alone is not…
  16. Compare5 marksStandardAnhydrous magnesium sulfate, MgSO4, and hydrated magnesium sulfate, MgSO4.7H2O, are two forms of the same salt. (a) Compare the formulas of these two compounds, using the terms anhydrous, hydrated and water of…
  17. Compare5 marksStandardBlue hydrated copper(II) sulfate, CuSO4.5H2O, turns white when heated. The white solid formed is anhydrous copper(II) sulfate, CuSO4. Compare the hydrated and anhydrous forms of copper(II) sulfate. In your answer…
  18. Explain4 marksStandardA student compares 1 mol of oxygen gas, O2, with 1 mol of hydrogen gas, H2, and finds that the oxygen sample has the greater mass. The student concludes that one mole of oxygen contains more molecules than one mole of…
  19. Suggest4 marksStandardIron reacts with chlorine to form iron(III) chloride, FeCl3. A student heats 5.6 g of iron powder with 3.55 g of chlorine gas and collects the product. Suggest, without calculating any numerical answer, how the student…
  20. Suggest4 marksStandardAcidified water was electrolysed using inert electrodes. The hydrogen and oxygen produced were collected and their volumes measured at the same temperature and pressure. The volume of hydrogen collected was twice the…
  21. Explain4 marksStandardCalcium nitrate crystallises from water as the hydrated salt Ca(NO3)2.4H2O. (a) Explain how the formula of the anhydrous salt, Ca(NO3)2, follows from the charges on the calcium and nitrate ions. (b) Explain what is…
  22. Suggest4 marksStandardA naturally occurring sample of element X contains two isotopes. The relative atomic mass of X in this sample is not a whole number. Suggest what is meant by the relative atomic mass of X, and suggest why the value is…
  23. Explain4 marksStandardThe relative atomic mass of hydrogen is 1.0 and that of oxygen is 16.0, based on the carbon-12 scale. With reference to the definition of the unified atomic mass unit, explain the meanings of relative atomic mass and…
  24. Compare5 marksStandardA student investigates two reactions. Reaction A: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) The student reacts 5.00 g of CaCO3 with 25.0 cm^3 of 2.00 mol dm^-3 HCl. Reaction B: N2(g) + 3H2(g) → 2NH3(g) The…
  25. Explain4 marksStandardA student is told that a white solid is a pure ionic compound containing only aluminium ions and oxide ions. Explain how the formula of this compound can be deduced from the charges on the ions. In your answer, state…
  26. Describe5 marksStandardDescribe what is meant by each of the following terms. (a) the unified atomic mass unit (b) relative atomic mass, Ar (c) relative isotopic mass (d) relative molecular mass, Mr (e) relative formula mass
  27. Explain4 marksStandardPropane has the molecular formula C3H8. Explain, in terms of the Avogadro constant, what is meant by one mole of propane molecules and what this amount of propane tells you about the amounts of carbon and hydrogen…
  28. Explain4 marksStandardA student determines the concentration of a sample of hydrochloric acid by adding an excess of calcium carbonate to 25.0 cm³ of the acid and collecting the carbon dioxide produced in a gas syringe. CaCO3(s) + 2HCl(aq)…
  29. Explain4 marksStandardWater has the formula H2O. Its relative molecular mass, Mr, is 18. Explain what is meant by the unified atomic mass unit, by the relative atomic mass of an element, and by the relative molecular mass of a molecule. Use…
  30. Compare5 marksStandardA student is studying the properties of neon gas and carbon dioxide gas. They want to understand how the masses of atoms and molecules are described. Compare the terms 'relative atomic mass' and 'relative molecular…
  31. Describe5 marksChallengeWater is sold in bottles, and the number of water molecules in one bottle is far too large to be counted individually. A manufacturer records the amount of water used in each batch in moles. The Avogadro constant is…
  32. Suggest6 marksChallengeBenzene, C6H6, and ethyne, C2H2, have the same empirical formula, CH. A student is given a third hydrocarbon, X, and is told only that its empirical formula is also CH. The student also has samples of anhydrous…
  33. Describe5 marksChallengeHydrochloric acid reacts with sodium hydroxide as shown. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) A student mixes 20.0 cm^3 of 2.00 mol dm^-3 hydrochloric acid with 40.0 cm^3 of 1.50 mol dm^-3 sodium hydroxide. Describe…
  34. Suggest6 marksChallengeA student is shown a 1 mol sample of hydrogen gas and a 1 mol sample of oxygen gas at the same temperature and pressure. The two gas samples occupy the same volume but have very different masses. Suggest, in terms of…
  35. Describe5 marksChallengeDescribe the reaction when an excess of zinc powder is added to an aqueous solution of copper(II) sulfate and the mixture is stirred until no further change occurs. The solution had been prepared by dissolving hydrated…
  36. Describe7 marksChallengeGreen hydrated chromium(III) sulfate has the formula Cr2(SO4)3.12H2O. When heated, it loses water of crystallisation to form the anhydrous salt. Describe: (a) the meaning of the terms hydrated, anhydrous and water of…
  37. Explain5 marksChallengeA student writes the following definition in a notebook. 'The relative atomic mass of an element is the mass of one atom of its most abundant isotope divided by one twelfth of the mass of a carbon-12 atom. The relative…
  38. Explain5 marksChallengeThe Avogadro constant is 6.02 × 10^23 mol^-1. Two students are discussing the mole. Student A: One mole of any substance contains the same number of elementary entities as 12 g of carbon-12, so 1 mol of ethanol and 1…
  39. Describe7 marksChallengeA sample of chlorine contains two isotopes, ce^35Cl and ce^37Cl. The relative atomic mass of chlorine is 35.5. Describe the meanings of the following terms, using chlorine as an example where appropriate: unified…
  40. Describe7 marksChallengeA student makes the following statement: 'One mole of carbon-12 atoms has a mass of 12 g and contains 6.02 × 10^23 atoms. One mole of oxygen-16 atoms has a mass of 16 g, so it must contain more atoms than one mole of…
  41. Describe5 marksChallengeSodium chloride is an ionic solid. Natural chlorine is a mixture of ce^35Cl and ce^37Cl atoms. (a) Describe what is meant by the unified atomic mass unit. (b) Describe what is meant by the relative atomic mass of…
  42. Explain5 marksChallengeAnhydrous iron(III) sulfate forms a hydrated salt with the formula Fe2(SO4)3.18H2O. (a) Explain, in terms of the ions present, why the formula of the anhydrous salt is Fe2(SO4)3 and not FeSO4 or Fe3(SO4)2. (b) Explain…
  43. Suggest6 marksChallengeAn element, E, has two naturally occurring isotopes. Samples of E taken from two different rock deposits give slightly different relative atomic masses. Suggest, in terms of the definitions of the unified atomic mass…
  44. Compare7 marksChallengeHydrated iron(II) sulfate, FeSO4.7H2O, is a pale green crystalline solid. On strong heating it changes to anhydrous iron(II) sulfate, a white solid. Both solids dissolve in water to give the same pale green solution…
  45. Suggest6 marksChallengeAcidified water was electrolysed using inert electrodes, and the hydrogen and oxygen produced were collected in graduated syringes at room temperature and pressure. In one run the volumes collected were 36.0 cm3 of…
  46. Describe6 marksChallengeChlorine exists as a mixture of isotopes, and chlorine gas consists of diatomic molecules. Describe what is meant by each of the following terms, using the unified atomic mass unit in your definitions. the unified…