Chemistry: Decomposition of Carbonates, Lattice Energy, and Transition Metal Complexes, Exams of Chemistry

Download Chemistry: Decomposition of Carbonates, Lattice Energy, and Transition Metal Complexes and more Exams Chemistry in PDF only on Docsity! * 8 9 3 6 5 2 3 Chemistry - 9701 -42 Paper 4 - A Level Structured Questions Question Paper - May - June 2023 AS and A Level - Cambridge International Examination Cambridge International AS & A Level CHEMISTRY 9701/42 Paper 4 A Level Structured Questions May/June 2023 2 hours You must answer on the question paper. No additional materials are needed. INSTRUCTIONS ● Answer all questions. ● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. ● Write your name, centre number and candidate number in the boxes at the top of the page. ● Write your answer to each question in the space provided. ● Do not use an erasable pen or correction fluid. ● Do not write on any bar codes. ● You may use a calculator. ● You should show all your working and use appropriate units. INFORMATION ● The total mark for this paper is 100. ● The number of marks for each question or part question is shown in brackets [ ]. ● The Periodic Table is printed in the question paper. ● Important values, constants and standards are printed in the question paper. This document has 24 pages. DC (CE/SG) 311841/5 © UCLES 2023 [Turn over 4 3 3 4 4 2 3 4 2 3 [Turn over© UCLES 2023 9701/42/M/J/ 23 (c) Potassium sulfite, K2SO3, is used as a food additive. The concentration of sulfite ions, SO 2–, can be determined by titration using aqueous acidified manganate(VII) ions, MnO –. 3 • A 250 cm3 solution contains 3.40 g of impure K2SO3.• 25.0 cm3 of this solution requires 22.40 cm3 of 0.0250 mol dm–3 acidifiedMnO – to reach the end-point. All the SO 2– 4 ions are oxidised. None of the other species in the impure K2SO3 are oxidised. The reaction occurs as shown by the two half-equations. H2O + SO 2– SO 2– + 2H+ + 2e– MnO – + 8H+ + 5e– Mn2+ + 4H O (i) Give the ionic equation for the reaction between SO 2– and acidified MnO –. ........................................................................................................................... .......... [1] (ii) Calculate the percentage purity of the sample of K2SO3. Show your working. percentage purity of K2SO3 =.......................[3] (d) Potassium disulfite, K2S2O5, is another food additive. The disulfite ion, S O 2–, has the 2 5 displayed formula shown in Fig. 1.2. O– O α S S O O O– Fig. 1.2 Deduce the geometry (shape) around the S(α) atom in S O 2–. 2 © UCLES 2023 9701/42/M/J/ 23 geometry around S(α).........................................[1] [Total: 13] 4 © UCLES 2023 9701/42/M/J/ 23 2 (a) State two typical chemical properties of a transition element. 1 ................................................................................................................................................ 2 ................................................................................................................................................ [1] (b) Aqueous solutions of cobalt(II) salts contain the complex ion [Co(H2O)6]2+. (i) Define complex ion. ........................................................................................................................... ................ ........................................................................................................................... .......... [1] (ii) Samples of [Co(H2O)6]2+ are reacted separately with an excess of aqueous ammonia, with an excess of concentrated HCl and with an excess of aqueous sodium hydroxide, as shown in Fig. 2.1. exces s NH3(aq ) A [Co(H2O)6]2+ (aq) excess NaOH(aq ) C excess concentrated HCl B Fig. 2.1 Complete Table 2.1 about the reactions shown by [Co(H2O)6]2+. Table 2.1 reagent added to [Co(H2O)6]2+ (aq) formula of cobalt species formed colour and state of cobalt species formed type of reaction an excess of NH3(aq) A = an excess of concentrated HCl B = 7 [Turn over© UCLES 2023 9701/42/M/J/ 23 3 (a) Complete Table 3.1 by placing one tick (✓) in each row to indicate the sign of each type of energy change under standard conditions. Table 3.1 energy change always positive always negative can be either negative or positive bond energy enthalpy change of atomisation enthalpy change of formation [1] (b) Define standard enthalpy change of atomisation. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) Table 3.2 shows some energy changes. Table 3.2 energy change value / kJ mol– 1 standard enthalpy change of atomisation of silver +285 first ionisation energy of silver +731 second ionisation energy of silver +2074 bond energy of O=O +496 bond energy of O–O +150 first electron affinity of oxygen –141 second electron affinity of oxygen +798 first ionisation energy of oxygen +1314 standard enthalpy change of formation of silver oxide, Ag2O(s) –31 8 © UCLES 2023 9701/42/M/J/ 23 Calculate the lattice energy, Δ o H latt, of Ag2O(s) using relevant data from Table 3.2. It may be helpful to draw a labelled energy cycle. Show your working. oΔH latt of Ag2O(s) = ........................................... kJ mol–1 [3] (d) Suggest the trend in the magnitude of the lattice energies of the silver compounds Ag2S, Ag2O and Ag2Se. Explain your answer. ......................................... ......................................... ......................................... least exothermic most exothermic .................................................................................................................................. ................. .................................................................................................................................. ................. ................................................................................................................................................... [2] 9 [Turn over© UCLES 2023 9701/42/M/J/ 23 (e) Silver sulfite, Ag2SO3(s), is sparingly soluble in water. (i) Give an expression for the solubility product, Ksp, of Ag2SO3. Ksp = [1] (ii) Calculate the equilibrium concentration of Ag+ in a saturated solution of Ag2SO3 at 298 K. [Ksp: Ag2SO3, 1.50 × 10–14 mol3 dm–9 at 298 K] o(f) The standard enthalpy change of solution, Δ [Ag+] = .............................. mol dm–3 [1] –1 H sol, of AgNO3(s) in water is +22.6 kJ mol . Suggest how the feasibility of dissolving AgNO3(s) in water changes with temperature. Explain your answer. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 12] 12 © UCLES 2023 9701/42/M/J/ 23 (b) In aqueous solution, iodide ions react with acidified hydrogen peroxide, as shown. 2I– + H2O2 + 2H+ I2 + 2H2O The initial rate of reaction is found to be first order with respect to I–, first order with respect to H2O2 and zero order with respect to H+. Fig. 4.1 shows a possible four-step mechanism for this reaction. step 1 step 2 H2O2 + I– H+ + IO– IO– + H2O HIO step 3 HIO + I– I2 + OH– step 4 OH– + H+ H2O Fig. 4.1 (i) Suggest which of the steps, 1, 2, 3 or 4, in this mechanism is the rate- determining step. Explain your answer. ........................................................................................................................... ................ ........................................................................................................................... ................ ........................................................................................................................... .......... [1] (ii) Identify a step in Fig. 4.1 that involves a redox reaction. Explain your answer in terms of oxidation numbers. ........................................................................................................................... ................ ........................................................................................................................... ................ ........................................................................................................................... .......... [1] (iii) Suggest the role of HIO in this mechanism. Explain your reasoning. ........................................................................................................................... ................ ........................................................................................................................... ................ ........................................................................................................................... 13 [Turn over© UCLES 2023 9701/42/M/J/ 23 .......... [1] [Total: 10] 14 © UCLES 2023 9701/42/M/J/ 23 5 (a) Methylbenzene can undergo different reactions, as shown in Fig. 5.1. H2 / Pt Br2 / UV light reaction 1 reaction 2 reaction 3 Br2 / FeBr3 + Fig. 5.1 (i) Draw structures in Fig. 5.1 for the possible organic products of the three reactions shown. [3] (ii) Complete Table 5.1. Table 5.1 type of reaction mechanism reaction 1 reaction 2 [2] (b) When methylbenzene reacts with an electrophile, a substitution reaction occurs. No addition reaction takes place under these conditions. Explain why no addition reaction takes place. .................................................................................................................................. ................. .................................................................................................................................. ........... [1] 17 [Turn over© UCLES 2023 9701/42/M/J/ 23 (ii) The reaction shown in Fig. 5.2 produces a small amount of a by-product, P, with the molecular formula C14H14OS. Suggest a structure for by-product P. [1] (d) Acyl bromides, RCOBr, can be synthesised by the reaction of a carboxylic acid and SOBr2. This is a similar reaction to the synthesis of acyl chlorides using SOCl 2. (i) Give an equation for the reaction between ethanoic acid and SOBr2. ..................................................................................................................................... [1] (ii) Suggest the relative ease of hydrolysis of acyl bromides, RCOBr, acyl chlorides, RCOCl, and alkyl chlorides, RCl. Explain your answer. ......................................... > ......................................... > ......................................... easiest to hydrolyse hardest to hydrolyse ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [3] [Total: 14] 18 © UCLES 2023 9701/42/M/J/ 23 6 (a) Perindopril is a drug used to treat heart disease. perindopril O H O O OH N O N Fig. 6.1 (i) State the number of chiral carbon atoms present in one molecule of perindopril. ........................................................................................................................... .......... [1] (ii) Suggest one benefit and one disadvantage of producing a drug such as perindopril as a single pure optical isomer. benefit ............................................................................................................... ................ ........................................................................................................................... ................ disadvantage ..................................................................................................... ................ ........................................................................................................................................... [2] (b) (i) Name all the functional groups in perindopril. ........................................................................................................................................... ..................................................................................................................................... [2] 19 [Turn over© UCLES 2023 9701/42/M/J/ 23 (ii) A sample of perindopril is hydrolysed with hot aqueous acid. Draw the structures of the three organic products of the complete acid hydrolysis of perindopril. [3] [Total: 8] 22 © UCLES 2023 9701/42/M/J/ 23 (ii) Draw the structure of the organic product, R, formed when phenol reacts with an excess of Br2(aq). [1] (iii) State the reagents and conditions for reaction 1 and reaction 2 in Fig. 7.1. reaction 1 .......................................................................................................................... reaction 2 .......................................................................................................................... [2] [Total: 8] Z, C6H13NO2 23 [Turn over© UCLES 2023 9701/42/M/J/ 23 8 (a) Describe the difference in reactivity between chloroethane and chlorobenzene with OH–(aq). Explain your answer. .................................................................................................................................. ................. .................................................................................................................................. ................. .................................................................................................................................. ................. .................................................................................................................................. ........... [2] (b) Compound T, C5H9O2Cl, is a useful synthetic intermediate. Fig. 8.1 shows some reactions of T. T O Cl O excess NaOH(aq ) + heat step 1 O NC O excess HCl (aq) heat + OH step 2 Fig. 8.1 Y XW 24 © UCLES 2023 9701/42/M/J/ 23 (i) Give the systematic name for T. ........................................................................................................................... .......... [1] (ii) Draw the structures of W, X, Y and Z in Fig. 8.1. [4] (iii) State the reagents and conditions for steps 1 and 2 in Fig. 8.1. step 1 ........................................................................................................................... ..... step 2 ........................................................................................................................... ..... [2] c c c 27 [Turn over© UCLES 2023 9701/42/M/J/ 23 9 (a) Define standard cell potential, E  o . .................................................................................................................................. ................. .................................................................................................................................. ........... [1] (b) An electrochemical cell is set up to measure E  o of a cell consisting of an Fe3+ / Fe2+ half-cell and a Cl 2 / Cl  – half-cell. Draw a labelled diagram of this electrochemical cell. Include all necessary substances. It is not necessary to state conditions used. [3] (c) The cell reaction for the electrochemical cell in (b) is shown. Cl 2 + 2Fe2+ 2Fe3+ + 2Cl– E  o = +0.59 V Calculate ΔG o , in kJ mol–1, for this cell reaction. ΔG o = .............................. kJ mol–1 [2] 23 (d) Another experiment is set up using the same electrochemical cell. In this experiment the Fe2+ concentration is 0.15 mol dm–3. All other concentrations remain at their standard values. The Nernst equation is shown. E = E o + (0.059 / z) log [oxidised species] [reduced species] (i) Use the Nernst equation to calculate the electrode potential, E, for the Fe3+ / Fe2+ half-cell in this experiment. [E o : Fe3+ / Fe2+ = +0.77 V] E = .............................. V [1] (ii) Use your answer to (d)(i) to calculate Ecell for this electrochemical cell. Ecell = .............................. V [1] [Total: 8] Important values, constants and standards molar gas constant R = 8.31 J K–1 mol–1 Faraday constant F = 9.65 × 104 C mol–1 Avogadro constant L = 6.022 × 1023 mol–1 electronic charge e = –1.60 × 10–19 C molar volume of gas Vm = 22.4 dm3 mol–1 at s.t.p. (101 kPa and 273 K) Vm = 24.0 dm3 mol–1 at room conditions ionic product of water Kw = 1.00 × 10–14 mol2 dm–6 (at 298 K (25 °C)) specific heat capacity of water c = 4.18 kJ kg–1 K–1 (4.18 J g–1 K–1) 24 © UCLES 2023 9701/42/M/J/ 23 © UCLES 2023 9701/42/M/J/23