Cambridge A Level Chemistry 9701 — 2020 May/June Paper 2 · Variant 1

1 Gallium is a metal in Group 13 of the Periodic Table. (a) There are two stable isotopes of gallium, 69Ga and 71Ga. (i) State, with reference to subatomic particles, how the isotopes 69Ga and 71Ga differ from each other. ............................................................................................................................................. ....................................................................................................................................... [1] (ii) State what further information is needed to calculate the relative atomic mass of gallium. ....................................................................................................................................... [1] (b) Gallium and its compounds show similar properties to aluminium and its compounds. Gallium reacts with excess chlorine to form gallium trichloride. (i) At 500 °C, gallium trichloride is a gas. Suggest the type of attraction that exists at 500 °C ●● between atoms within a gallium trichloride molecule ............................................................................................................................................. ●● between gallium trichloride molecules. ............................................................................................................................................. [2] (ii) When gallium trichloride is cooled a solid, Ga2Cl 6, forms. Suggest the name of the attraction formed between two gallium trichloride molecules to form Ga2Cl 6. ....................................................................................................................................... [1] (c) Gallium metal reacts rapidly when exposed to air. A white solid layer is formed on its surface. (i) Suggest an equation to describe the reaction occurring when gallium metal is exposed to air. ....................................................................................................................................... [2] (ii) The table gives the formula of each gallium-containing product formed when gallium oxide reacts separately with hot aqueous hydrochloric acid and hot aqueous sodium hydroxide. formula of gallium-containing product hot aqueous hydrochloric acid GaCl 3 hot aqueous sodium hydroxide NaGa(OH)4 Give the name of the type of behaviour shown by gallium oxide in these reactions. ....................................................................................................................................... [1] [Total: 8]

Mark scheme: 1(a)(i) (different) number of neutrons. 1 1(a)(ii) the relative abundance / % abundance of (each) the isotopes. 1 1(b)(i) M1 attractions between atoms within a gallium trichloride molecule covalent (bonds) M2 attractions between gallium trichloride molecules temporary induced dipoles 2 1(b)(ii) coordinate / dative (covalent) 1 1(c)(i) 4Ga + 3O2 → 2Ga2O3 M1 correct formula of Ga2O3 M2 correctly balanced equation based on Ga + O2 and formula of gallium oxide in M1 2 1(c)(ii) amphoteric 1

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2 (a) The equation shown in (a)(i) describes the reaction which occurs when aqueous potassium iodide is added to aqueous copper(II) sulfate. A white precipitate of copper(I) iodide forms in a brown solution of iodine and potassium sulfate. (i) Balance the equation and include state symbols. ......CuSO4(.....) + ......KI(.....) → ......CuI(.....) + ......I2(.....) + ......K2SO4(.....) [2] The table gives the oxidation numbers of iodine in the different species in the equation. iodine-containing species oxidation number of iodine KI –1 CuI –1 I2 0 (ii) Deduce the oxidation number of copper in CuSO4 and CuI. ●● oxidation number of copper in CuSO4 ................................ ●● oxidation number of copper in CuI ..................................... [1] (iii) Describe the type of reaction shown by the equation in (a)(i). Explain your answer in terms of electron transfer. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (b) In the reaction described in (a)(i), a student uses 17.43 g of CuSO4•yH2O. By further titration of the reaction products the student concludes that the total amount of CuSO4 in the sample is 0.0982 mol. Use the Data Booklet to complete the table to calculate the value of y, where y is an integer. Show your working. mass of 0.0982 mol CuSO4 .............................. g amount of H2O in 17.43 g of CuSO4•yH2O .............................. mol H2O value of y y = .............................. [4] [Total: 9]

Mark scheme: 2(a)(i) M1 correct balancing M2 correct state symbols 2(a)(ii) Oxidation state of copper in CuSO4 (+)2 AND Oxidation state of copper in CuI (+)1 1 2(a)(iii) M1 redox 1 M2 iodide ions – lost electron(s) AND copper ions – gained electron(s) 1 Question Answer Marks 2(b) Mass of 0.0982mol CuSO4 in 17.43g CuSO4.yH2O M1 calculate Mr CuSO4 using Ar from data booklet 63.5 + 32.1 + 64.0 = 159.6 M2 use Mr to calculate mass of CuSO4 (0.0982 × M1) =15.67272g number of water in 17.43g of CuSO4 yH2O M3 calculate the mass amount of water in sample AND use this value to calculate the amount of water present (17.43-15.67)/18 = 0.097778 mol value of y M4 use the ratio of M2: 0.0982 to find y (mol H2O ÷ mol CuSO4) = 1 4

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3 Nitric acid, HNO3, can be made by reacting nitrogen dioxide with water. The enthalpy change for the reaction can be measured indirectly using a Hess’ cycle. ∆Hr 3NO2(g) + H2O(l) 2HNO3(l) + NO(g) (a) Explain what is meant by the term enthalpy change of formation. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (b) Complete the Hess’ cycle using the values given in the table and hence calculate the enthalpy change, ∆Hr, for this reaction. Show your working. substance ∆Hf / kJ mol–1 NO2(g) 34.0 H2O(l) –286 HNO3(l) –173 NO(g) 91.1 ∆Hr 3NO2(g) + H2O(l) 2HNO3(l) + NO(g) ∆Hr = .............................. kJ mol–1 [3] (c) Nitrogen and oxygen do not react at normal atmospheric temperatures. Explain why. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] Nitrogen oxides can be formed naturally in the Earth’s atmosphere from nitrogen and oxygen in the air. (d) State one way that nitrogen oxides are produced naturally. .............................................................................................................................................. [1] (e) Nitrogen dioxide, NO2, acts as a homogeneous catalyst in the oxidation of atmospheric sulfur dioxide. (i) Explain why NO2 is described as a homogeneous catalyst. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [3] (ii) Write equations which describe the two reactions occurring when NO2 acts as a catalyst in the formation of sulfur trioxide from sulfur dioxide. ............................................................................................................................................. ....................................................................................................................................... [2] [Total: 13]

Mark scheme: 3(a) M1 (enthalpy / energy change) when one mole of a compound/substance is formed M2 from its elements in their standard states 2 3(b) M1 use of correct stoichiometry in calculation 3x∆Hf NO2 1x-∆Hf H2O 2x∆Hf HNO3 1x∆Hf NO M2 correct signs associated with the appropriate ∆Hf values/terms used for the calculation of ∆Hreaction M3 ∆Hreaction = –(102 – 286) + (–346 + 91.1) = –70.9 kJ mol–1 3 3(c) M1 nitrogen has a triple bond M2 EITHER high energy is needed to break the bond OR at normal temperatures there is not enough energy to break the bond / to overcome the activation energy 2 3(d) lightning 1 Question Answer Marks 3(e)(i) M1 define homogeneous (homogeneous catalyst is) in the same phase / state as the reactants M2 and M3 Define catalyst All 3 points scores 2 marks. Any 2 points scores 1 mark increase the rate AND lowers the activation energy AND without being chemically altered at the end of the reaction / are regenerated at the end of the reaction 3(e)(ii) M1 NO2 + SO2  NO + SO3 M2 NO + ½ O2  NO2 2

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4 Calcium nitrate, Ca(NO3)2, reacts with ammonia, carbon dioxide and water to form a mixture of ammonium nitrate and calcium carbonate. Ca(NO3)2 + 2NH3 + CO2 + H2O → 2NH4NO3 + CaCO3 (a) Explain why ammonia is described as a Brønsted‑Lowry base in this reaction. .............................................................................................................................................. [1] The product mixture can then be added to soil. (b) State two reasons why this mixture of products is added to some soils. 1 ................................................................................................................................................. 2 ................................................................................................................................................. [2] (c) Complete the table to name the shape and give the bond angle of each species. name of shape bond angle / ° CO2 NH3 H2O [3] [Total: 6]

Mark scheme: 4(a) Accepts a proton / H+ (ion) 1 4(b) Two reasons why product mixture is added to soil – allow in any order M1 Acts as a fertiliser / adds nutrients (for plants) M2 Neutralise acid soils / increases the pH of acid soil 2 4(c) name of shape bond angle / ° CO2 Linear 180 NH3 Pyramid(al) 107 H2O non-linear / V / bent 104.5 All 6 correct – 3 marks 4 or 5 correct – 2 marks 2 or 3 correct – 1 mark 3

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5 (a) Below is a list of species which can react with organic compounds. CN– HCl Cl H2O CO32– (i) From the list, identify a species which can react with ethane. ....................................................................................................................................... [1] (ii) From the list, identify two species which can attack the π bond in ethene. ....................................................................................................................................... [1] (iii) From the list, identify a species which can be used to distinguish between solutions of propanoic acid and propan-1-ol. Describe any relevant observations. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (b) Cl (g) can be made from Cl 2(g). (i) Describe the conditions required for this process. ....................................................................................................................................... [1] (ii) Name this process. ....................................................................................................................................... [1] (c) (i) Name an organic functional group which reacts with a nucleophile in an addition reaction. ....................................................................................................................................... [1] (ii) Name an organic functional group which tends to react with a nucleophile in an SN1 substitution mechanism. ....................................................................................................................................... [1] (d) But-1-ene reacts with steam in the presence of concentrated phosphoric acid to form two isomers of molecular formula C4H10O. Each reaction occurs via a different intermediate ion. (i) Draw the structure of both intermediate ions. [2] (ii) Circle the more stable intermediate ion drawn in (d)(i). Explain your answer. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] [Total: 12]

Mark scheme: 5(a)(i) 1 5(a)(ii) HCl AND H2O 1 5(a)(iii) M1 CO32– M2 propanoic acid – effervesce. (Propan-1-ol – no reaction) 2 5(b)(i) ultraviolet light / uv 1 5(b)(ii) homolytic fission (of chlorine (gas) / Cl2) 1 5(c)(i) carbonyl / aldehyde / ketone 1 5(c)(ii) tertiary halogenoalkane 1 5(d)(i) Two structures representing the intermediate M1 C2H5C+HCH3 M2 CH3CH2CH2C+H2 2 5(d)(ii) Identify the most stable intermediate M1 C2H5C+HCH3 explanation M2 (more / 2 alkyl groups attached so) it has the greater inductive / electron donating effect 2

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6 2-methylbut-1-ene reacts with acidified manganate(VII) ions, under specific conditions, to produce two organic compounds X and Y. X immediately reacts with the acidified manganate(VII) ions to form carbon dioxide and water. Y has the structural formula CH3CH2COCH3. acidified manganate(VII) ions X Y 2-methylbut-1-ene + CH3CH2COCH3 CO2 + H2O (a) Draw the skeletal formula of 2-methylbut-1-ene. [1] (b) (i) State the specific conditions required for the acidified manganate(VII) ions to react with 2-methylbut-1-ene in this way. ....................................................................................................................................... [1] (ii) Name the type of reaction occurring to the functional group in 2‑methylbut‑1‑ene in the reaction in (b)(i). ....................................................................................................................................... [1] (c) Draw the structural formula of X. .............................................................................................................................................. [1] (d) Describe a chemical test and the expected observation(s) to confirm the presence of the carbonyl functional group in Y. .................................................................................................................................................... .............................................................................................................................................. [2] (e) The infra-red spectrum of 2-methylbut-1-ene is shown. 1 0.8 0.6 relative transmittance 0.4 0.2 4000 3000 2000 1000 wavenumber / cm–1 Predict two main differences that would be seen between the spectra of Y, CH3CH2COCH3, and of 2-methylbut-1-ene. Give reasons for your predictions. Your answer should refer only to the region of each spectrum above 1500 cm–1. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (f) Propanoic acid, CH3CH2CO2H, is reduced by LiAl H4. (i) Write an equation to show this reaction. Use [H] to represent an atom of hydrogen from the reducing agent. ....................................................................................................................................... [1] (ii) Name the organic product formed in this reaction. ....................................................................................................................................... [1] (g) Organic compound W is an ester which is a structural isomer of propanoic acid. (i) State the molecular formula of W. ....................................................................................................................................... [1] (ii) Draw a possible structure of W. [1] [Total: 12]

Mark scheme: 6(a) 1 6(b)(i) hot AND concentrated 1 6(b)(ii) oxidation 1 Question Answer Marks 6(c) Structural formula of X: HCO2H OR HCOOH 1 6(d) M1 reagent (2,4–) DNPH / (2,4)-dinitrophenylhydrazine M2 observation yellow / orange / red precipitate 2 6(e) Predict two differences, with reasons, between spectra of Y, CH3CH2COCH3 and 2-methylbut-1-ene (shown) first difference M1 absence of peak/ absorption at 3100 (cm–1) as no longer any =C–H present (in Y) second difference M2 peak at 1650 (cm-1) moves to the left to any value / range of values between 1670 and 1740) due to disappearance of C=C (in Y) and appearance of C=O (in Y) OR absence of peak at 1650 (cm-1) as no longer any C=C present (in Y) AND appearance of peak (in Y) at (any value / range of values) between 1670-1740(cm-1) due to C=O 2 6(f)(i) CH3CH2CO2H + 4[H] → CH3CH2CH2OH + H2O 1 6(f)(ii) propan-1-ol ALLOW propan-2-ol as error carried forward from 6f(i) 1 6(g)(i) Molecular formula of W C3H6O2 1 6(g)(ii) Possible structure of W CH3COOCH3 OR HCOOCH2CH3 1

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