Chemistry 9701/21 May/June 2024: question paper and mark scheme

Question

(a) The elements of Group 17 are called halogens. Complete Table 1.1. Table 1.1 halogen colour at 293 K chlorine bromine iodine [1] (b) State the trend in volatility of the halogens chlorine, bromine and iodine. Explain your answer. …… [3] (c) Iodine is made by reacting bromine with sodium iodide. (i) Construct an ionic equation for the reaction of bromine with sodium iodide. …… [1] (ii) State the role of bromine in the reaction. Explain your answer. …… [1] (d) Concentrated sulfuric acid is added to separate samples containing equal amounts of NaCl , NaBr and NaI. All three samples initially react to produce the hydrogen halide. (i) Write an equation to describe the acid–base reaction that occurs when concentrated sulfuric acid reacts with NaBr. …… [1] (ii) Deduce which sodium halide, NaCl , NaBr or NaI, produces the largest percentage yield of hydrogen halide when concentrated sulfuric acid is added. Explain your answer by considering the relative reactivity of the halide ions as reducing agents. identity of sodium halide …… explanation …… [3] [Total: 10]

Question

(a) Sulfur chloride, SCl 2, is a liquid at room temperature. When SCl 2 is added to water, misty fumes are seen and a solution is made that turns universal indicator red. (i) Identify the type of reaction that occurs when SCl 2 is added to water. …… [1] (ii) Name a chloride of a different Period 3 element that is also a liquid at room temperature and produces misty fumes when added to water. …… [1] (b) A molecule of SCl 2 contains two S–Cl covalent bonds. (i) Complete the dot-and-cross diagram in Fig. 2.1 to show the arrangement of the outer electrons in a molecule of SCl 2. Use × to show electrons from the chlorine atoms. Use ● to show electrons from the sulfur atom. Cl S Cl Fig. 2.1 [2] (ii) Predict the shape of, and bond angle in, a molecule of SCl 2 by using VSEPR theory. shape …… bond angle …… [2] (c) Solid magnesium nitride, Mg3N2, is a crystalline solid. (i) Deduce the oxidation numbers of magnesium and nitrogen in magnesium nitride to complete Table 2.1. Table 2.1 oxidation number in Mg3N2 magnesium nitrogen [1] (ii) Magnesium nitride reacts with an excess of water to produce ammonia and magnesium hydroxide only. Construct an equation to describe this reaction. …… [1] (iii) Explain why the solution produced in the reaction in (c)(ii) has a pH greater than 7. Refer to the products of the reaction in your answer. …… [2] (d) Boron nitride is a white solid that melts above 2900 °C. Fig. 2.2 shows part of the lattice structure of a crystal of boron nitride. boron atom nitrogen atom van der Waals’ forces covalent bond Fig. 2.2 (i) Use Fig. 2.2 to deduce the empirical formula of boron nitride. …… [1] (ii) Suggest the identity of another crystalline solid that has atoms arranged in layers similar to that of solid boron nitride. …… [1] [Total: 12]

Question

(a) Define Le Chatelier’s principle. …… [2] (b) Reaction 1 describes the reversible reaction between yellow Fe3+(aq) and colourless SCN–(aq) to produce red FeSCN2+(aq). reaction 1 Fe3+(aq) + SCN–(aq) FeSCN2+(aq) ∆H = –x kJ mol–1 yellow colourless red A mixture of Fe3+(aq), SCN–(aq) and FeSCN2+(aq) is at equilibrium at 20 °C. The temperature of this mixture is then increased to 50 °C and allowed to reach equilibrium. Deduce the changes that occur, if any, in the equilibrium mixture at 50 °C compared to the equilibrium mixture at 20 °C. • change in appearance • change in relative concentration of FeSCN2+(aq) • change in value of the equilibrium constant, Kc [3] (c) In another experiment, equimolar amounts of Fe3+(aq) and SCN–(aq) are mixed together and allowed to reach equilibrium. The total volume of the mixture is 25.0 cm3. reaction 1 Fe3+(aq) + SCN–(aq) FeSCN2+(aq) At equilibrium the mixture contains: • [SCN–] = 1.30 × 10–3 mol dm–3 • [FeSCN2+] = 0.300 × 10–3 mol dm–3. (i) Calculate the initial amount, in mol, of Fe3+(aq) added to SCN–(aq) to produce this mixture. initial amount of Fe3+(aq) = …… mol [2] (ii) Calculate Kc for reaction 1 and state its units. Show your working. Kc = …… units …… [2] [Total: 9]

Question

(a) Define enthalpy change of formation. …… [2] (b) Iron is made when iron(III) oxide is heated with carbon monoxide, as shown by reaction 2. reaction 2 Fe2O3 + 3CO 2Fe + 3CO2 Table 4.1 shows enthalpy change of formation data measured at 298 K and 101 kPa. Table 4.1 substance equation value for ∆H of / kJ mol–1 Fe2O3 –824.2 CO –110.5 CO2 C(s) + O2(g) CO2(g) –393.5 (i) Complete Table 4.1 by adding equations with relevant state symbols to represent: • standard enthalpy change of formation for Fe2O3 • standard enthalpy change of formation for CO. [2] (ii) Use the data in Table 4.1 to calculate the enthalpy change of reaction, ∆Hr , in kJ mol–1, for reaction 2. Show your working. ∆Hr = …… kJ mol–1 [2] [Total: 6]

Question

Hydrocarbon molecules contain covalent bonds. (a) Define covalent bond. …… [1] (b) A C=C bond in an alkene is made from a σ bond and a π bond. (i) Identify the hybridisation of the carbon atoms in a C=C bond in an alkene. …… [1] (ii) Draw labelled diagrams to show, in terms of orbital overlap, how the σ and π bonds are made in a C=C bond. σ bond π bond [2] (c) In electrophilic reactions involving alkenes the π bond of C=C is broken. (i) Suggest one difference between σ and π bonds that explains why the π bond is broken in electrophilic addition reactions involving alkenes. …… [1] (ii) Complete Fig. 5.1 to show the mechanism for the electrophilic addition of hydrogen bromide to 2-methylpropene to produce the major organic product. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. H CH3 H C C CH3 H Br Fig. 5.1 [4] [Total: 9]

Question

(a) V shows stereoisomerism. V O O O Fig. 6.1 (i) Explain what is meant by stereoisomerism. …… [1] (ii) Deduce the number of stereoisomers of V. Explain your reasoning. …… [2] (iii) Deduce the molecular formula of V. …… [1] (iv) Name all the functional groups present in V. …… [1] (b) Fig. 6.2 shows two reactions involving V. V O O O reaction 1 reaction 2 + reagent T + reagent U W X OH OH O O O O Fig. 6.2 (i) Identify the role of reagent T for each functional group that reacts in reaction 1. …… [1] (ii) Suggest the identity of reagent U in reaction 2. …… [1] (c) Both functional groups in one molecule of Y react with an inorganic reagent to form one molecule of Q and one molecule of methanol, CH3OH, as shown in Fig. 6.3. Y O O inorganic reagent Q + CH3OH O Fig. 6.3 (i) Part of the mass spectrum for Q is shown in Fig. 6.4. Only peaks with m / e greater than 198 are shown. relative 100 abundance x 198 199 200 201 m/e Fig. 6.4 Calculate the relative abundance, x, of the peak at m / e = 201. Show your working. x = …… [2] (ii) Q contains only hydroxyl functional groups. Complete Table 6.1 to show the observations that occur when 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) is added to separate samples of Y and Q. Table 6.1 observation on addition of 2,4-DNPH reagent Y Q [1] (iii) Under certain conditions, 0.0020 mol of Q reacts with an excess of sodium to produce a total of 44.8 cm3 of gas at s.t.p. Calculate the number of hydroxyl groups present in a molecule of Q. Show your working. number of hydroxyl groups = …… [2] (iv) Use Table 6.2 to describe and explain two differences between the infrared spectrum of Y and Q in the region above 1500 cm–1. …… [2] Table 6.2 bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide 1640–1690 carbonyl, carboxyl 1670–1740 ester 1710–1750 C≡N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 O–H carboxyl 2500–3000 hydroxy 3200–3650 [Total: 14] 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 at www.cambridgeinternational.org after the live examination series. 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 16 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 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 138.9 140.1 140.9 144.2 – 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. 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