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

1 Gallium is an element in Group 13. A sample of gallium is analysed using a mass spectrometer. The mass spectrum produced is shown. 60.11% 39.89% % relative abundance 69 71 mass (a) Explain what is meant by the term relative atomic mass. .................................................................................................................................................... .............................................................................................................................................. [2] (b) Calculate the relative atomic mass of gallium in this sample. Give your answer to 4 significant figures. Show your working. relative atomic mass = .............................. [2] (c) Complete the table which describes a gaseous atom of gallium. total number type of orbital which nucleon isotope of electrons in contains the electron in number lowest energy level the highest energy level 71Ga [3] (d) When gallium is heated in excess chlorine, gallium trichloride, GaCl 3, is made. Draw the shape of the gallium trichloride molecule and suggest the Cl –Ga–Cl bond angle. shape of molecule bond angle ................................................................. [2] (e) Gallium oxide, Ga2O3, and aluminium oxide react in the same way with HCl (aq) and with NaOH(aq). (i) Suggest the equation for the reaction between Ga2O3 and HCl (aq). ....................................................................................................................................... [1] (ii) Suggest an equation for the reaction between gallium oxide and NaOH(aq). ....................................................................................................................................... [2] [Total: 12]

Mark scheme: 1(a) EITHER M1 (weighted) average/mean mass of the isotope(s)/an atom(s) M2 relative to 1/12 of the mass (of an atom) of 12C (where an atom of 12C is exactly12). OR M1 mass of one mol of atoms M2 relative / compared to 1/12 (the mass) of 1 mol of C-12 OR in which one mol C-12 (atom) has a mass of (exactly) 12 g 2 1(b) M1 60.11/100 x 69 + 39.89/100x71 M2 69.80 2 1(c) isotope nucleon number total number of electrons in lowest energy level type of orbital contains the electron in the highest energy level 71Ga M1 71 M2 2 M3 p (-orbital) 3 1(d) M1 shape M2 bond angle 120(°) 2 1(e)(i) Ga2O3+ 6HCl  2GaCl3 + 3H2O 1 Question Answer Marks 1(e)(ii) M1 Identity of correct gallium containing product NaGa(OH)4 OR NaGaO2 M2 correctly balanced equation for reaction of Ga2O3 with NaOH(aq) EITHER Ga2O3+ 2NaOH + 3H2O  2NaGa(OH)4 OR Ga2O3+ 2NaOH  2NaGaO2 + H2O 2

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2 Nitric acid can be made in a 3-stage process. Stage 1 Ammonia is oxidised by oxygen from the air, to form nitrogen monoxide and water. This reaction is carried out at 10–13 atmospheres pressure and 900 °C in the presence of a platinum catalyst. Stage 2 Nitrogen monoxide reacts with more oxygen to form nitrogen dioxide. 2NO + O2 2NO2 ∆H = –114 kJ mol–1 Stage 3 Nitrogen dioxide reacts with water to make nitric acid and nitrogen monoxide. 3NO2 + H2O → 2HNO3 + NO (a) Write an equation to show the reaction occurring in stage 1. .............................................................................................................................................. [1] (b) Draw a ‘dot-and-cross’ diagram to show the arrangement of outer electrons in a molecule of ammonia. [1] (c) (i) In the boxes, give the oxidation numbers of nitrogen in the nitrogen-containing species for the reaction in stage 3. 3NO2 + H2O → 2HNO3 + NO [2] (ii) Explain why the reaction in stage 3 is described as a disproportionation reaction. Include reference to transfer of electrons in your answer. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (d) The release of nitrogen monoxide into the atmosphere causes atmospheric pollution. State and explain the effect of nitrogen monoxide gas in contact with moist air. .................................................................................................................................................... .............................................................................................................................................. [2] (e) The nitric acid made in stage 3 can then be reacted with ammonia to form ammonium nitrate. Stage 3 3NO2 + H2O → 2HNO3 + NO NH3 + HNO3 → NH4NO3 Calculate the volume of nitrogen dioxide, measured at room temperature and pressure, required to make 40 tonnes of ammonium nitrate. [1 tonne = 1000 kg] Show your working. volume of nitrogen dioxide = .............................. [3] (f) State one use of ammonium nitrate. .............................................................................................................................................. [1] [Total: 12]

Mark scheme: 2(a) 4NH3 + 5O2 → 4NO + 6H2O 2(b) xx H x N x H x H 1 2(c)(i) 3NO2 + H2O → 2HNO3 + NO 3 correct oxidation numbers – 2 marks 2 correct oxidation numbers – 1 mark 2 2(c)(ii) relates the term disproportionation to the reaction described M1 nitrogen /N (in nitrogen dioxide) is both gaining electrons and losing electrons during the reaction M2 refer to relevant transfer of electrons when NO2 reacts to form HNO3 and NO NO2 to HNO3 involves loss of electron(s) AND NO2 to NO involves gain of electron(s) (+)4 (+)5 (+)2 Question Answer Marks 2(d) M1 state the effect of NO gas on contact with moist air NO reacts with water OR NO reacts with oxygen and water. M2 consequence of M1 in terms of atmospheric pollution causing acid rain OR photochemical smog / ground level ozone OR destroy ozone layer 2 2(e) M1 number of mol in sample of NH4NO3 40t NH4NO3 = 500 000 mol ammonium nitrate M2 ratio of mol NO2: NH4NO3 3/2 mol NO2 :1 mol NH4NO3 M3 volume of no mol NO2 at rtp using 1 mol = 24dm3 18 000 000 dm3 of NO2 3 2(f) fertiliser 1

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3 Sucrose, C12H22O11, reacts with water to form glucose and fructose in reaction A. glucose fructose O H O CH2OH C C H C OH HO C H HO C H H C OH C12H22O11 + H2O + H C OH H C OH H C OH CH2OH CH2OH reaction A (a) Suggest a name for this type of reaction. .............................................................................................................................................. [1] (b) Explain in detail, why glucose and fructose are a pair of structural isomers. Your answer should refer specifically to these two molecules. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (c) Reaction A occurs faster in the presence of an enzyme. This is reaction B. (i) The activation energy for reaction B is +29 kJ mol–1. Predict a value for the activation energy of reaction A. ....................................................................................................................................... [1] (ii) The enthalpy change for reaction A is –14 kJ mol–1. Predict a value for the enthalpy change for reaction B. ....................................................................................................................................... [1] (iii) Sketch a labelled energy level diagram for reaction B. Use relevant values from (c)(i) and (c)(ii). energy / kJ mol–1 progress of reaction [2] (d) 1.00 g of sucrose, C12H22O11, is completely combusted. The heat energy produced is used to increase the temperature of 250 g of water inside a calorimeter from 25.0 °C to 40.7 °C. These data can be used to calculate the enthalpy change of combustion of sucrose. (i) Explain what is meant by the term enthalpy change of combustion of sucrose. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Use the Data Booklet to calculate the enthalpy change, in kJ mol–1, for the combustion of sucrose. Assume that all of the heat energy produced is transferred to the water. Show your working. enthalpy change of combustion of sucrose = .............................. kJ mol–1 [3] [Total: 12]

Mark scheme: 3(a) hydrolysis 1 3(b) M1 both have molecular formula - C6H12O6 M2 idea that in glucose and fructose there are the same number and type of atoms present but the atoms are arranged in a different order ie one has a carbonyl group at the end of the chain/molecule and the other has a carbonyl group in the middle of the chain/molecule 2 3(c)(i) value for the activation energy for the reaction A (no enzyme) compared to reaction B (with enzyme) value / range of values that are more (+) 29 kJ mol-1 1 3(c)(ii) value for the enthalpy change for reaction A (no enzyme) compared to reaction B (with enzyme) -14 kJ mol-1 1 Question Answer Marks 3(c)(iii) M1 show the energy of the reactants > products AND label ∆H using the predicted value given in (ii) M2 show activation energy ‘hump’ AND label using the value given in (i) 2 3(d)(i) M1 (enthalpy change) when 1 mole of sucrose M2 burns/combusts/reacts in excess air/oxygen OR completely burns/combusts/reacts in air/oxygen 2 3(d)(ii) M1 for finding amount of energy released per gram of sucrose using ∆H /Q = mc∆T OR ∆H = – mc∆T = (-)250x4.18x(40.7-25) = (-)16406.5 J per gram OR(-)16.4065 kJ / g M2 for finding amount (mol) sucrose in1g = 1/342 mol M3 = M1 / (M2x1000) ∆H = - 5610 kJ mol-1 (3 sig figs) OR -5611 kJ mol-1 (4 sig figs) 3

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4 (a) An unlabelled bottle contains a straight-chain halogenoalkane, Q. The molecular formula of Q is C5H11X, where X is a halogen; bromine, chlorine or iodine. A test is carried out to identify the halogen present in Q. A sample of Q is added to NaOH(aq) and warmed. Dilute nitric acid is then added followed by a few drops of aqueous silver nitrate. A cream precipitate is observed. (i) Suggest the identity of X. ....................................................................................................................................... [1] (ii) Write an ionic equation to describe the formation of the cream precipitate. Include state symbols. ....................................................................................................................................... [1] (iii) Describe a further test which would confirm the identity of X. test ...................................................................................................................................... expected result .................................................................................................................... [2] (b) The reaction of Q with NaOH(aq) tends to proceed via an SN2 mechanism. (i) Suggest the structural formula of the straight-chain halogenoalkane Q. [1] (ii) Explain why the reaction tends to proceed via an SN2 mechanism rather than an SN1 mechanism. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (c) Two different halogenoalkanes, P and R, both with the molecular formula C4H9Cl, are separately dissolved in ethanol and heated under reflux with sodium hydroxide. The major organic product of each of these reactions is methylpropene. (i) Name the type of reaction occurring. ....................................................................................................................................... [1] (ii) Write an equation, using molecular formulae, to represent the reaction occurring. ....................................................................................................................................... [1] (iii) Draw the skeletal formula of methylpropene. [1] (iv) Give the names of P and R. ....................................................................................................................................... [2] [Total: 12]

Mark scheme: 4(a)(i) Bromine / Br 1 4(a)(ii) Ag+(aq) + X-(aq)  AgX(s) OR Ag+(aq) + Br-(aq)  AgBr(s) 1 4(a)(iii) M1 reagent Add (aqueous) ammonia M2 expected result EITHER (Dilute ammonia) – partial amount precipitate dissolves OR not much precipitate dissolves OR add concentrated ammonia – precipitate dissolves 2 Question Answer Marks 4(b)(i) CH3CH2CH2CH2CH2Br 1 4(b)(i) M1 primary/ 1o (carbo)cation formed is not very stable M2 EITHER (as) only one alkyl group exerting an inductive effect OR only one alkyl group so the charge is (more) localised on the C+ 2 4(c)(i) elimination 1 4(c)(ii) C4H9Cl + NaOH → C4H8 + NaCl + H2O 1 4(c)(iii) ONLY 1 4(c)(iv) M1 2-chloro(-2-)methylpropane M2 1-chloro(-2-)methylpropane ALLOW in any order 2

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5 The reaction sequence shows how ethene, C2H4, can be converted into other organic molecules. C2H4 reaction 1 reaction 5 OH Cl reaction 2 reaction 6 O NH2 reaction 3 HO N reaction 4 heat with dilute acid W (a) Complete the table to give ●● the name of the reaction mechanisms of reactions 1 and 6 ●● the reagents and conditions required for reactions 1, 2 and 6. name of name of reagents reaction mechanism and conditions 1 2 6 [6] (b) In reaction 3 the organic molecule reacts with HCN and a KCN catalyst. (i) Complete the diagram to show the mechanism of the reaction occurring. Include all relevant dipoles, lone pairs and curly arrows in your answer. H H H – C O H3C C O H3C C OH H3C CN CN C – H C C – N N N [3] (ii) Name the functional groups present in the product of reaction 3. ....................................................................................................................................... [2] (c) Draw the structure of the organic molecule W formed in reaction 4. [1] [Total: 12]

Mark scheme: 5(a) Rxn. name of mechanism Name of reagents and conditions 1 M1 electrophilic addition M2 steam AND concentrated phosphoric acid (catalyst) 2 M3 & M4 Two marks for name of reagent and both conditions. One mark for name of reagent and one conditions acidified potassium dichromate ((VI)) condition 1 warm condition 2 distil NOT reflux 6 M5 nucleophilic substitution M6 ammonia (alcoholic) AND heat in a sealed tube / heat under pressure 6 5(b)(i) mechanism for ethanal and HCN using CN- (from KCN) as the catalyst M1arrow from lone pair of electrons on :CN- to C of C=O M2 correct dipole on Cδ+=Oδ- AND arrow from the double bond to or beyond the O of C=O M3 arrow from lone pair of electrons on O of intermediate to H of HCN AND arrow from H-C bond to C of H-C≡N 3 Question Answer Marks 5(b)(ii) ALLOW in any order M1 nitrile M2 (secondary) alcohol 2 5(b)(iii) ALLOW any unambiguous structure 1

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