Chemistry 9701/23 October/November 2025: question paper and mark scheme

Question

Chromium, Cr, and its compounds are widely used in many chemical reactions. (a) Cr exists as four stable isotopes. (i) The most common isotope of Cr is chromium-52. Determine the number of protons, neutrons and electrons in an atom of chromium-52. number of protons …… neutrons …… electrons …… [1] (ii) Describe how an atom of chromium-54 differs from an atom of chromium-52. Refer to numbers of particles in your answer. …… [1] (iii) The relative isotopic masses of the isotopes of Cr can be determined using mass spectrometry. State what other information is needed to calculate the relative atomic mass, Ar , of Cr. …… [1] (iv) Atoms of 52Cr, 53Cr and 54Cr make up more than 95% of naturally occurring chromium atoms. The Ar of naturally occurring Cr is 51.996. Suggest what these statements imply about the relative isotopic mass of the fourth stable isotope of chromium. …… [1] (b) The shorthand electronic configuration of chromium is [Ar] 3d54s1. (i) Complete the full electronic configuration of chromium. …… 3d54s1 [1] (ii) Deduce the total number of unpaired electrons in an atom of chromium. …… [1] * 0000800000003 * DFD 3 (c) Acidified dichromate(VI) ions will convert methanal, CH2O, to carbon dioxide. The movement of electrons to or from relevant species is shown in the following half-equations. half-equation 1 CH2O + H2O CO2 + 4H+ + 4e– half-equation 2 Cr2O72– + 14H+ + 6e– 2Cr3+ + 7H2O (i) Identify the species that is reduced in half-equation 2. Explain your answer. …… [1] (ii) The oxidation state of the carbon atom in methanal is 0. Calculate the oxidation state of carbon in carbon dioxide. …… [1] (iii) Construct the ionic equation for the reaction of dichromate(VI) ions with methanal in acidic conditions. …… [2] (iv) Methanal is a liquid at –30 °C but carbon dioxide is a gas at this temperature. Explain why. …… [2] * 0000800000004 * DFD 4 (d) In acidic conditions, a dynamic equilibrium is established between CrO42–(aq) and Cr2O72–(aq). 2CrO42–(aq) + 2H+(aq) Cr2O72–(aq) + H2O(l) ΔH > 0 (i) State what is meant by dynamic equilibrium. …… [1] (ii) Identify the condition necessary to establish dynamic equilibrium. …… [1] (iii) CrO42–(aq) ions are yellow and Cr2O72–(aq) ions are orange. State what is observed when the following changes are made to an equilibrium mixture of acidified CrO42–(aq) and Cr2O72–(aq) ions. Explain your answers. • The equilibrium mixture is warmed gently. observation …… explanation …… • Dilute HCl (aq) is added to the equilibrium mixture. observation …… explanation …… [4] (e) Chromium(IV) fluoride, CrF4, is a covalent molecule that shows similar chemical properties to SiCl 4. Suggest the type of reaction that occurs when CrF4 is placed in water. Construct a relevant equation for this reaction. type of reaction …… equation …… [2] [Total: 20] * 0000800000005 * DFD 5 * 0000800000006 * DFD 6

Question

The Period 3 elements show trends in physical and chemical properties across the period. (a) Fig. 2.1 shows the variation in atomic and ionic radii of the Period 3 elements Na to Cl . The ionic radius of Si is not shown. 250 200 150 Key radius / pm atomic radius 100 ionic radius 50 0 Na Mg Al Si P S Cl Fig. 2.1 (i) Explain the trend shown in the atomic radii of the Period 3 elements Na to Cl . …… [2] (ii) Explain why there is a large difference in the ionic radii of Al and P. …… [2] * 0000800000007 * DFD 7 (b) Table 2.1 gives some information about some of the Period 3 oxides. Row B gives the pH of the solution that forms when the Period 3 oxide is added to water. Table 2.1 formula of Period 3 oxide Na2O MgO Al 2O3 SiO2 P4O10 SO3 oxidation number of A +3 Period 3 element B pH of solution — — (i) Complete Table 2.1. [2] (ii) State why there is no data given in row B for Al 2O3 and SiO2. …… [1] (c) (i) Write an equation for the reaction of Na2O with dilute hydrochloric acid. …… [1] (ii) Construct an equation for the reaction of Al 2O3 with a base to form NaAl O2. …… [1] (d) Group 2 nitrates decompose on heating to form oxides. (i) State the trend in thermal stability of the Group 2 nitrates down the group. …… [1] (ii) Identify the other products of the thermal decomposition of Group 2 nitrates. …… [1] [Total: 11] * 0000800000008 * DFD 8

Question

Cycloalkanes show similar chemical properties to alkanes but have the same empirical formula as alkenes. (a) Define empirical formula. …… [1] (b) Cyclopentane, C5H10, has four cyclic structural isomers. One of these isomers is C, shown in Fig. 3.1. Complete Fig. 3.1 to show two other cyclic structural isomers of C5H10. cyclopentane C Fig. 3.1 [2] (c) Cyclopentane reacts with Cl 2 in the presence of ultraviolet light to form C5H9Cl. (i) The reaction is initiated by the bond fission of Cl 2. State the type of bond fission shown in the initiation step. …… [1] (ii) Complete the equations to show the two propagation steps that follow the initiation step. propagation 1 C5H10 + …… C5H9• + …… propagation 2 C5H9• + …… …… [2] (iii) The final step is shown. C5H9• + Cl • C5H9Cl Give the name for this step in the reaction. …… [1] * 0000800000009 * DFD 9 (d) Fig. 3.2 shows a reaction cycle involving cyclopentane, cyclopentene and C5H9Cl . ΔH2 reaction 1 reaction 2 H2 Cl2 ΔH3 = –53 kJ mol–1 Cl reaction 3 Fig. 3.2 (i) Identify a suitable reagent for reaction 3. …… [1] (ii) Use the data in Fig. 3.2 and in Table 3.1 to calculate the enthalpy change of reaction 2, ΔH2. Table 3.1 enthalpy change of compound combustion, ΔHc / kJ mol–1 –3292 –3115 H2 –286 ΔH2 = …… kJ mol–1 [2] * 0000800000010 * DFD 10 (e) Cyclopentene, C5H8, reacts with hot concentrated acidified KMnO4 to form compound W, C5H8O4. (i) Draw the structure of W. [1] (ii) The infrared spectrum of W is shown in Fig. 3.3. 100 transmittance / % 50 0 4000 3000 2000 1500 1000 500 wavenumber / cm–1 Fig. 3.3 Identify two absorptions in the infrared spectrum of W that would not be present in the infrared spectrum of cyclopentene. • Write 1 or 2 on Fig. 3.3 against each of these two absorptions. • Complete Table 3.2 to show which bond is responsible for each absorption that you have identified in Fig. 3.3. Table 3.2 absorption 1 2 bond responsible [2] * 0000800000011 * DFD 11 Table 3.3 characteristic infrared absorption range bond functional groups containing the bond (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 amide 1640–1690 C=O carbonyl, carboxyl 1670–1740 ester 1710–1750 C N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 carboxyl 2500–3000 O–H hydroxy 3200–3650 [Total: 13] * 0000800000012 * DFD 12

Question

Fig. 4.1 shows a possible synthesis of propene, C3H6. reaction 1 reaction 2 reaction 3 C2H5COOH C2H5CH2OH C2H5CH2Cl C3H6 NaOH Fig. 4.1 (a) (i) Identify the type of reaction that occurs in reaction 1. …… [1] (ii) Suggest a suitable reagent for reaction 2. …… [1] (iii) Reaction 3 is an elimination reaction. Write an equation for this reaction and identify the solvent and conditions used. equation …… solvent and conditions …… [2] (iv) C2H5CH2OH can be directly converted to C3H6. Suggest the reagent and conditions for this conversion. …… [1] (b) Under suitable conditions, propene polymerises to form poly(propene). Poly(propene) exhibits stereoisomerism. (i) Identify the type of polymerisation that forms poly(propene) from propene. …… [1] (ii) Define stereoisomerism. …… [2] * 0000800000013 * DFD 13 (iii) Draw a section of poly(propene), showing two repeat units. Use your diagram to identify the type of stereoisomerism shown by poly(propene). Explain your answer. section of poly(propene) [3] (iv) State two difficulties associated with the disposal of poly(propene). 1 …… 2 …… [2] * 0000800000014 * DFD 14 (c) Under different conditions, two molecules of propene can combine to form compounds X and Y. X Y (i) Name X. …… [1] (ii) Fig. 4.2 shows the mass spectrum of either compound X or compound Y. 100 80 60 relative abundance 40 20 0 10 20 30 40 50 60 70 80 m/e Fig. 4.2 Identify which of X and Y gives this mass spectrum. Give one reason for your answer, referring to the fragmentation pattern. …… [1] (iii) The molecular ion peak in the spectrum in Fig. 4.2 has relative abundance 34.7. Calculate the relative abundance of the [M+1]+ peak in this spectrum. relative abundance of [M+1]+ peak = …… [1] [Total: 16] * 0000800000015 * DFD 15 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 = 6.02 × 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 DFD 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. 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