Chemistry 9701/42 May/June 2022: question paper and mark scheme

Question

(a) The solubility of the Group 2 hydroxides increases down the group. Explain this trend. . …… . …… . …… . …… . …… [3] (b) The solubility of Be(OH)2 in water is 2.40 × 10–6 g dm–3 at 298 K. (i) Write an expression for the solubility product, Ksp, of Be(OH)2 and state its units. Ksp = units = …… [2] (ii) Calculate the numerical value of Ksp for Be(OH)2 at 298 K. Ksp = …… [2] (c) Be(OH)2 is soluble in aqueous solutions containing an excess of hydroxide ions and forms the complex ion [Be(OH)4]2–. This complex ion has a similar shape to that of [CuCl 4]2–. (i) Define the term complex ion. . …… . …… [1] (ii) Draw a three-dimensional diagram to show the structure of the complex ion [Be(OH)4]2–. Name the shape of the [Be(OH)4]2– complex ion. shape . …… [1] (d) (i) Explain why transition elements can form complex ions. . …… . …… [1] (ii) Complete Table 1.1 to show the coordination number of each metal ion, and the shapes and overall polarities of the complex ions listed. Table 1.1 coordination polar or complex ion shape number non-polar cis-[Pt(H2NCH2CH2NH2)Cl 2] square planar [Ag(NH3)2]+ non-polar [Fe(C2O4)3]3– 6 [2] (e) (i) Define stability constant, Kstab. . …… . …… [1] (ii) Nickel can form complexes with the ligands en, H2NCH2CH2NH2, and tn, H2NCH2CH2CH2NH2, as shown. equilibrium 1 [Ni(H2O)6]2+ + 3en [Ni(en)3]2+ + 6H2O Kstab = 6.76 × 1017 equilibrium 2 [Ni(H2O)6]2+ + 3tn [Ni(tn)3]2+ + 6H2O Kstab = 1.86 × 1012 Construct an expression for the stability constant, Kstab, for equilibrium 1. State the units for Kstab. Kstab = units = …… [2] (iii) Describe what the Kstab values indicate about the position of equilibrium for equilibrium 1 and 2. Use the Kstab values to deduce which complex, [Ni(en)3]2+ or [Ni(tn)3]2+, is more stable. . …… . …… [1] [Total: 16]

Question

(a) Explain why transition elements have variable oxidation states. . …… . …… [1] (b) Sketch the shape of a 3dxy orbital. z y x [1] (c) Explain why transition elements form coloured compounds. . …… . …… . …… . …… . …… . …… [3] (d) Aqueous solutions of copper(II) salts contain [Cu(H2O)6]2+ ions. Equilibrium 3 and equilibrium 4 show two reactions of these ions. equilibrium 3 [Cu(H2O)6]2+(aq) + 2OH–(aq) Cu(OH)2(s) + 6H2O(l) equilibrium 4 [Cu(H2O)6]2+(aq) + 4NH3(aq) [Cu(NH3)4(H2O)2]2+(aq) + 4H2O(l) (i) State the colour of Cu(OH)2(s) and [Cu(NH3)4(H2O)2]2+(aq). colour of Cu(OH)2(s) …… colour of [Cu(NH3)4(H2O)2]2+(aq) …… [1] (ii) Use Le Chatelier’s principle to explain why a precipitate is formed when NaOH(aq) is added dropwise to [Cu(H2O)6]2+(aq). . …… . …… . …… [1] (e) There are two possible stereoisomers with the formula [Cu(NH3)4(H2O)2]2+. Draw three-dimensional diagrams to show the two stereoisomers. Cu Cu [2] [Total: 9]

Question

(a) (i) Define first electron affinity. . …… . …… . …… [2] (ii) The first electron affinity of an atom is usually an exothermic process, whereas the second electron affinity is an endothermic process. Suggest why. . …… . …… [1] (iii) Describe the general trend in first electron affinities for Cl, Br and I. Explain your answer. . …… . …… . …… [2] (b) Table 3.1 shows energy changes to be used in this question and in (c). Table 3.1 energy change value / kJ mol–1 standard enthalpy change of atomisation of zinc +131 first ionisation energy of zinc +906 second ionisation energy of zinc +1733 standard enthalpy change of formation of ZnI2(s) –208 lattice energy, , of zinc iodide, ZnI2(s) –2605 first ionisation energy of iodine +1008 second ionisation energy of iodine +1846 I–I bond energy +151 enthalpy change of sublimation of iodine, I2(s) → I2(g) +62 Calculate the first electron affinity for iodine. Use relevant data from Table 3.1 in your working. It may be helpful to draw a labelled energy cycle. Show all working. first electron affinity for iodine = …… kJ mol–1 [3] (c) Predict how of CdI2(s) differs from of ZnI2(s). Place a tick (✓) in the appropriate box in Table 3.2. Table 3.2 of CdI2(s) is less of CdI2(s) is the of CdI2(s) is more negative than of ZnI2(s) same as of ZnI2(s) negative than of ZnI2(s) Explain your answer. . …… . …… [1] [Total: 9]

Question

(a) Calcium carbonate decomposes on heating. CaCO3(s) → CaO(s) + CO2(g) Table 4.1 shows the values of the Gibbs free energy change, ∆G o, for this reaction at various temperatures. Table 4.1 T/K ∆G o / kJ mol–1 1050 9.9 1085 4.3 1120 –1.3 1148 –5.8 1176 –10.3 Assume the standard enthalpy change, ∆H o, and the standard entropy change, ∆S o, for this reaction remain constant over this temperature range. (i) Use the data in Table 4.1 to plot a graph of ∆G o against T on the grid. 12.5 10.0 7.5 5.0 G o / kJ mol–1 2.5 0.0 T/K 1040 1060 1080 1100 1120 1140 1160 1180 1200 –2.5 –5.0 –7.5 –10.0 –12.5 [2] (ii) Calculate the gradient of your graph. Determine the ∆S o in J K–1 mol–1 for this reaction. Show all working. ∆S o = …… J K–1 mol–1 [2] (b) Group 1 hydrogencarbonates, MHCO3, decompose on gentle heating to give the corresponding metal carbonate, carbon dioxide and water vapour. (i) Write an ionic equation for the decomposition of the hydrogencarbonate ion. . …… [1] (ii) The thermal stability of Group 1 hydrogencarbonates increases down the group. Suggest an explanation for the trend in thermal stability of the Group 1 hydrogencarbonates. . …… . …… . …… . …… [2] (c) The buffer system in seawater contains a mixture of HCO3– and H2CO3. equilibrium 5 H2CO3 + H2O HCO3– + H3O+ (i) Define a buffer solution. . …… . …… . …… [2] (ii) Construct two equations to show how equilibrium 5 acts as a buffer solution. . …… . …… [2] (iii) The [HCO3–] / [H2CO3] ratio in a sample of seawater is 14.1. Calculate the pH of this sample. [pKa: H2CO3, 6.35] pH = …… [3] [Total: 14]

Question

(a) Complete Table 5.1 to predict the substance liberated at each electrode during electrolysis of the indicated electrolyte with inert electrodes. Table 5.1 substance liberated substance liberated electrolyte at the anode at the cathode PbBr2(l) concentrated NaCl (aq) Cu(NO3)2(aq) [3] (b) An electrolytic cell is set up to determine a value for the Avogadro constant, L. The electrolyte is dilute sulfuric acid and both electrodes are copper. When a current of 0.600 A is passed through the acid for 30.0 minutes, the anode decreases in mass by 0.350 g. (i) State the relationship between the Faraday constant, F, and the Avogadro constant, L. . …… [1] (ii) Use the experimental information in (b) and data from the table on page 23 to calculate a value for the Avogadro constant, L. Show all working. Avogadro constant, L = …… [4] [Total: 8]

Question

(a) The reagent and conditions required for the nitration of benzene, benzoic acid and phenol are shown in Table 6.1. Table 6.1 compound reagents and conditions for nitration benzene concentrated HNO3, 50 °C, concentrated H2SO4 catalyst benzoic acid concentrated HNO3, 100 °C, concentrated H2SO4 catalyst phenol dilute HNO3(aq), 20 °C Concentrated HNO3 reacts with concentrated H2SO4 to generate the electrophile NO2+. (i) Complete Fig. 6.1 to show the mechanism of the reaction between benzene and NO2+. Include all relevant curly arrows and charges. NO2+ Fig. 6.1 [3] (ii) Write an equation to show how H2SO4 is regenerated. . …… [1] (b) Draw the major products from the mononitration of benzoic acid and of phenol. major product from benzoic acid major product from phenol [2] (c) Compare the relative ease of nitration of benzene, benzoic acid and phenol. Explain your reasoning; include reference to the structures of the three compounds in your answer. …… > …… > …… easiest least easy . …… . …… . …… . …… . …… [4] (d) The azo compound Congo Red is used as an acid–base indicator and can be made by the route shown in Fig. 6.2. In step 3 of this synthesis, compound Y reacts with compound Z. Compound Z is made from compound X. Assume that the –SO3– Na+ groups do not react. X C12H12N2 step 1 O2N NO2 step 2 Y C10H8NO3SNa Z + NaOH(aq) step 3 Congo Red NH2 N SO3– Na+ N N SO3– Na+ N NH2 Fig. 6.2 (i) Suggest structures for compounds X, Y and Z and draw them in the boxes in Fig. 6.2. [3] (ii) Give the reagents and conditions for step 1 and step 2. step 1 . …… step 2 . …… [3] [Total: 16]

Question

(a) State the uses of TMS and D2O in NMR spectroscopy. TMS …… D2O …… [1] (b) The three isomeric ketones with molecular formula C5H10O are: ● pentan-2-one ● entan-3-one p ● -methylbutanone. 3 (i) Complete Table 7.1 to show the number of peaks observed in the proton (1H) NMR spectrum and in the carbon-13 NMR spectrum for each compound listed. Table 7.1 number of peaks observed in number of peaks observed in ketone the proton (1H) NMR spectrum the carbon-13 NMR spectrum pentan-2-one pentan-3-one 3-methylbutanone [2] (ii) State all the ketones with molecular formula C5H10O that have: a doublet in their proton (1H) NMR spectrum . …… a singlet in their proton (1H) NMR spectrum. . …… [2] (c) Cortisone, C21H28O5, is a naturally occurring chemical that contains chiral carbon atoms. cortisone OH O CH3 O OH CH3 O Fig. 7.1 (i) Deduce the number of chiral carbon atoms in one molecule of cortisone. . …… [1] (ii) Cortisone is reacted with an excess of NaBH4. State the molecular formula of the organic compound formed. . …… [1] (iii) Cortisone is an optically active molecule. Explain what is meant by optically active. . …… . …… . …… [1] [Total: 8]

Question

(a) Compare the relative acidities of ethanol, ethanoic acid, chloroethanoic acid and phenol. Explain your reasoning. …… > …… > …… > …… most acidic least acidic . …… . …… . …… . …… . …… . …… [4] (b) An excess of ethanedioic acid, HOOCCOOH(aq), is reacted with warm acidified KMnO4(aq). State the type of reaction undergone by ethanedioic acid. Describe what you would observe. Write an equation for this reaction. Your equation can use [O] or [H] as necessary. type of reaction …… observations …… equation . …… [2] (c) A section of a polyester is shown. polyester O O O O O CH2 C O CH C O CH2 C O CH C CH3 CH3 Fig. 8.1 Draw the structures of the two monomers that form this polyester. [2] (d) Serine can polymerise to form two different types of condensation polymer; a polyester and a polypeptide. serine OH H2C O H2N C C H OH Fig. 8.2 Draw the structure of the polypeptide showing two repeat units. The peptide linkage should be shown displayed. [2] (e) Explain why condensation polymers normally biodegrade more readily than addition polymers. . …… . …… [1] [Total: 11]

Question

The structure of cyclohexylamine is shown in Fig. 9.1. cyclohexylamine NH2 Fig. 9.1 (a) Compare the relative basicities of ammonia, cyclohexylamine and phenylamine. Explain your reasoning. …… > …… > …… most basic least basic . …… . …… . …… . …… . …… [3] (b) Cyclohexylamine reacts with ethanoyl chloride to form the corresponding amide, L. L O C NH2 HN CH3 CH3COCl Fig. 9.2 (i) Name the mechanism for the reaction shown in Fig. 9.2. . …… [1] (ii) Complete the mechanism of the reaction between cyclohexylamine and CH3COCl. R–NH2 is used to represent cyclohexylamine. Include all relevant lone pairs of electrons, curly arrows, charges and partial charges. O H 3C C products Cl R NH2 [4] (iii) The reaction between cyclohexylamine and an excess of CH3COCl forms compound M. Compound M has the molecular formula C10H17NO2. Suggest and draw the structure of M. [1] [Total: 9] 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) The Periodic Table of Elements Group 1 2 13 14 15 16 17 18 1 2 H He hydrogen helium Key 1.0 4.0 3 4 atomic number 5 6 7 8 9 10 Li Be atomic symbol B C N O F Ne lithium beryllium name boron carbon nitrogen oxygen fluorine neon 6.9 9.0 relative atomic mass 10.8 12.0 14.0 16.0 19.0 20.2 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar sodium magnesium aluminium silicon phosphorus sulfur chlorine argon 23.0 24.3 3 4 5 6 7 8 9 10 11 12 27.0 28.1 31.0 32.1 35.5 39.9 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton 39.1 40.1 45.0 47.9 50.9 52.0 54.9 55.8 58.9 58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 at www.cambridgeinternational.org after the live examination series. Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon 85.5 87.6 88.9 91.2 92.9 95.9 – 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3 55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 lanthanoids Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 24 caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon 132.9 137.3 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 – – – 87 88 89–103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 actinoids Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson – – – – – – – – – – – – – – – – – 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 lanthanoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium 138.9 140.1 140.9 144.4 – 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.1 175.0 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 actinoids Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium – 232.0 231.0 238.0 – – – – – – – – – – – Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge