9701 Chemistry November 2025 Question Paper 23

1 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] , ,

(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 Cr2O7 2– + 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] , ,

(d) In acidic conditions, a dynamic equilibrium is established between CrO4 2–(aq) and Cr2O7 2–(aq). 2CrO4 2–(aq) + 2H+(aq) Cr2O7 2–(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) CrO4 2–(aq) ions are yellow and Cr2O7 2–(aq) ions are orange.

State what is observed when the following changes are made to an equilibrium mixture of acidified CrO4 2–(aq) and Cr2O7 2–(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] , ,

2 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. 0 Na Mg Al Si P S Cl 50 100 150 250 200 radius / pm atomic radius ionic radius Key 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] , ,

(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 A oxidation number of Period 3 element +3 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] , ,

3 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] , ,

(d) Fig. 3.2 shows a reaction cycle involving cyclopentane, cyclopentene and C5H9Cl . ΔH2 reaction 2 Cl2 reaction 1 H2 reaction 3 ΔH3 = –53 kJ mol–1 Cl 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 compound enthalpy change of combustion, ΔHc / kJ mol–1 –3292 –3115 H2 –286

ΔH2 = kJ mol–1 [2] , ,

(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. 4000 0 50 transmittance / % 100 3000 2000 1500 wavenumber / cm–1 1000 500 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] , , Table 3.3 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 carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3650

[Total: 13] , ,

4 Fig. 4.1 shows a possible synthesis of propene, C3H6. C2H5COOH C2H5CH2OH reaction 1 reaction 2 reaction 3 NaOH C2H5CH2Cl C3H6 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] , ,

(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] , ,

(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. 10 20 30 40 50 m / e 60 70 80 0 20 40 60 relative abundance 80 100 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] , , 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) , , Group The Periodic Table of Elements 1 H hydrogen 1.0 2 He helium 4.0 1 2 13 14 15 16 17 18 3 4 5 6 7 8 9 10 11 12 3 Li lithium 6.9 4 Be beryllium 9.0 atomic number atomic symbol Key name relative atomic mass 11 Na sodium 23.0 12 Mg magnesium 24.3 19 K potassium 39.1 20 Ca calcium 40.1 37 Rb rubidium 85.5 38 Sr strontium 87.6 55 Cs caesium 132.9 56 Ba barium 137.3 87 Fr francium – 88 Ra radium – 5 B boron 10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 81 Tl thallium 204.4 6 C carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sn tin 118.7 82 Pb lead 207.2 22 Ti titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium 178.5 104 Rf rutherfordium – 23 V vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium – 24 Cr chromium 52.0 42 Mo molybdenum 95.9 74 W tungsten 183.8 106 Sg seaborgium – 25 Mn manganese 54.9 43 Tc technetium – 75 Re rhenium 186.2 107 Bh bohrium – 26 Fe iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium – 27 Co cobalt 58.9 45 Rh rhodium 102.9 77 Ir iridium 192.2 109 Mt meitnerium – 28 Ni nickel 58.7 46 Pd palladium 106.4 78 Pt platinum 195.1 110 Ds darmstadtium – 29 Cu copper 63.5 47 Ag silver 107.9 79 Au gold 197.0 111 Rg roentgenium – 30 Zn zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200.6 112 Cn copernicium – 114 Fl flerovium – 116 Lv livermorium – 7 N nitrogen 14.0 15 P phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 83 Bi bismuth 209.0 8 O oxygen 16.0 16 S sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium – 9 F fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 53 I iodine 126.9 85 At astatine – 10 Ne neon 20.2 18 Ar argon 39.9 36 Kr krypton 83.8 54 Xe xenon 131.3 86 Rn radon – 113 Nh nihonium – 115 Mc moscovium – 117 Ts tennessine – 118 Og oganesson – 21 Sc scandium 45.0 39 Y yttrium 88.9 57–71 lanthanoids 89–103 actinoids 57 La lanthanum 138.9 89 Ac lanthanoids actinoids actinium – 58 Ce cerium 140.1 90 Th thorium 232.0 59 Pr praseodymium 140.9 91 Pa protactinium 231.0 60 Nd neodymium 144.2 92 U uranium 238.0 61 Pm promethium – 93 Np neptunium – 62 Sm samarium 150.4 94 Pu plutonium – 63 Eu europium 152.0 95 Am americium – 64 Gd gadolinium 157.3 96 Cm curium – 65 Tb terbium 158.9 97 Bk berkelium – 66 Dy dysprosium 162.5 98 Cf californium – 67 Ho holmium 164.9 99 Es einsteinium – 68 Er erbium 167.3 100 Fm fermium – 69 Tm thulium 168.9 101 Md mendelevium – 70 Yb ytterbium 173.1 102 No nobelium – 71 Lu lutetium 175.0 103 Lr lawrencium – , ,