Cambridge A Level Chemistry 9701 — 2025 Oct/Nov Paper 2 · Variant 2

1 Manganese, Mn, and its compounds are widely used in many chemical reactions. (a) Mn is usually found as a single isotope, manganese-55. (i) Determine the number of protons, neutrons and electrons in an atom of manganese-55. number of protons .......................... neutrons .......................... electrons .......................... [1] (ii) Define isotopes. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) A sample of manganese from the Moon is found to contain manganese-53 in addition to manganese-55. State the two pieces of information needed to determine the relative atomic mass, Ar , of manganese in this sample. 1 ........................................................................................................................................ 2 ........................................................................................................................................ [2] (b) The shorthand electronic configuration of manganese is [Ar] 3d5 4s2. (i) Complete the full electronic configuration of manganese. ......................................................................... 3d5 4s2 [1] (ii) Deduce the total number of unpaired electrons in an atom of manganese. ..................................................................................................................................... [1] (c) Manganese(IV) oxide reacts with methanal, CH2O, in acidic conditions to produce 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 MnO2 + 4H+ + 2e– Mn2+ + 2H2O (i) Identify the species that is reduced in half-equation 2. Explain your answer. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) The oxidation state of carbon in methanal is 0. Calculate the oxidation state of carbon in carbon dioxide. ..................................................................................................................................... [1] (iii) Construct the ionic equation for the reaction of manganese(IV) oxide with methanal in acidic conditions. ..................................................................................................................................... [2] [Total: 10]

Mark scheme: Question Answer Marks 1(a)(i) 25 protons 30 neutrons 25 electrons 1 1(a)(ii) (atoms of an element) with the same number of protons and different number of neutrons 1 1(a)(iii) M1 (relative) isotopic mass. 2 OR (relative isotopic) mass of Mn-55 and Mn-53 M2 (relative) abundance of each isotope 1(b)(i) 1s2 2s2 2p6 3s2 3p6 (3d5 4s2) 1 1(b)(ii) 5 1 1(c)(i) Mn / MnO2 AND it gains electrons 1 1(c)(ii) (+)4 1 1(c)(iii) Due to an issue with question 1(c)(iii), the question has been removed from the question paper. N/A

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2 The Period 3 elements show trends in physical and chemical properties across the period. (a) (i) Explain why the elements Na to Al are good electrical conductors. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Explain why the elements P, S and Cl do not conduct electricity. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Fig. 2.1 shows the variation in melting point of the Period 3 elements Si to Cl. 1800 1600 1400 1200 1000 melting point / K 800 600 400 200 0 Si P S Cl Fig. 2.1 The Period 3 elements Si to Cl are all non-metals. Explain why there is a large difference between the melting point of Si and the melting points of P, S and Cl. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) Table 2.1 gives some information about some Period 3 chlorides. Row B refers to the pH of the solution that forms when the Period 3 chloride is added to water. Table 2.1 formula of Period 3 chloride NaCl MgCl Al Cl PCl 2 3 SiCl4 5 oxidation number of A element bonded to Cl B pH of solution 6.5 C bonding ionic D structure giant Complete Table 2.1. You may use the following abbreviations. I = ionic, C = covalent, M = metallic G = giant, S = simple [4] (d) (i) Write an equation for the formation of Al Cl from its elements. 3 ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Write an equation for the formation of H3PO4 from PCl 5. ..................................................................................................................................... [1] (e) S2Cl2(l) reacts with Cl2(g) in a reversible reaction to form SCl2(l). Under certain conditions, a dynamic equilibrium is established. S2Cl2(l) + Cl2(g) 2SCl2(l) ΔH = – 41 kJ mol–1 (i) State what is meant by dynamic equilibrium. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Identify the condition necessary to establish dynamic equilibrium. ..................................................................................................................................... [1] (iii) S2Cl2(l) is yellow and SCl2(l) is red. S2Cl2(l) + Cl2(g) 2SCl2(l) ΔH = – 41 kJ mol–1 State what is observed when the following changes are made to an equilibrium mixture of S2Cl2(l) and SCl2(l). Explain your answers. • The equilibrium mixture is warmed gently. observation ................................................................................................................ explanation ................................................................................................................ .................................................................................................................................... .................................................................................................................................... • The overall pressure of the equilibrium mixture is increased. observation ................................................................................................................ explanation ................................................................................................................ .................................................................................................................................... .................................................................................................................................... [4] (f) Aqueous MgCl reacts with aqueous to form a white precipitate. Upon heating, the 2 Na2CO3 white precipitate undergoes thermal decomposition. (i) Construct an equation to show the reaction of aqueous MgCl with aqueous 2 Na2CO3. Use state symbols in your equation. ..................................................................................................................................... [2] (ii) Identify the products of the thermal decomposition of the white precipitate. ..................................................................................................................................... [1] (iii) State the trend in thermal stability of the Group 2 carbonates down the group. ..................................................................................................................................... [1] [Total: 20]

Mark scheme: 2(a)(i) delocalised electrons move (through the structure / between layers) 1 2(a)(ii) P / S / Cl have no charge carriers 1 OR (no ions and) no delocalised electrons OR no mobile / moving ions 2(b) M1 Si has (lots of) strong covalent bonds broken 2 M2 P / S / Cl (only) has weak Van der Waals’ (forces) broken 2(c) 4 M1 +1 +2 +3 +4 +5 M2 7 6.5 0–4 0–4 0–4 M3 I I I C C M4 G G G S S 2(d)(i) 2Al + 3Cl2 → 2AlCl3 1 2(d)(ii) PCl5 + 4H2O → H3PO4 + 5HCl 1 2(e)(i) rate of forward and backward (reaction) are the same / equal 1 OR (ratio of) concentrations of reactants and products are constant 2(e)(ii) closed system 1 2(e)(iii) M1 (mixture / solution becomes more) yellow 4 M2 (forward) reaction is exothermic (equilibrium shifts left) OR equilibrium / reaction shifts (left) to absorb (additional) heat / energy M3 (mixture / solution becomes more) red M4 fewer moles of gas on right-hand side OR (gas on left and) no gas on the right 2(f)(i) MgCl2(aq) + Na2CO3(aq) → MgCO3(s) + 2NaCl(aq) 2 M1 formulae in balanced equation M2 state symbols 2(f)(ii) MgO / magnesium oxide AND CO2 / carbon dioxide 1 2(f)(iii) (thermal stability) increases (down the group) 1

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3 The alkanes are a homologous series of organic molecules. Alkanes are generally unreactive and are commonly used as fuels. (a) Define homologous series. ................................................................................................................................................... ............................................................................................................................................. [2] (b) Give two reasons to explain the general unreactivity of alkanes. 1 ................................................................................................................................................ 2 ................................................................................................................................................ [2] (c) Alkanes with low relative molecular mass, Mr , are more useful than those found in heavier crude oil fractions. Name the process that is used to obtain alkanes with low Mr from heavier crude oil fractions. ............................................................................................................................................. [1] (d) Hexane, C6H14, has four structural isomers. Fig. 3.1 shows hexane and two of its structural isomers. hexane A B C D Fig. 3.1 (i) Complete Fig. 3.1 by drawing structures for C and D, the other two structural isomers of hexane. [2] (ii) A, B and hexane have different boiling points. Arrange A, B and hexane in order of increasing boiling point. Explain your answer. lowest .................................... < .................................... < .................................... highest ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [3] (e) Hexane can be converted into compounds E and F at high temperature and pressure. Fig. 3.2 shows the reaction scheme involving hexane, E and F. ∆H1 = +215 kJ mol−1 ∆H2 reaction 1 reaction 2 E F 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 formation, ∆Hf / kJ mol−1 −156 +48 ΔH2 = ........................................... kJ mol–1 [2] (iii) Write an equation for the complete combustion of hexane. ..................................................................................................................................... [1] [Total: 14]

Mark scheme: 3(a) M1 (family of molecules / compounds / series with) same general formula 2 OR (family of molecules where) molecular formula differs (only) by (units of) CH2(n). M2 similar chemical properties / reactions 3(b) M1 strong C—H (bonds) 2 M2 non-polar (C—H / molecule / bonds) 3(c) cracking 1 3(d)(i) 2 M1 M2 3(d)(ii) M1 B < A < hexane. 3 M2 hexane / unbranched has stronger / more IMFs M3 hexane / unbranched requires most / more energy 3(e)(i) H2 ((g)) OR hydrogen (gas) 1 3(e)(ii) M1 +215 + (–156) – (+48) = 2 M2 +11 kJ mol–1 3(e)(iii) C6H14 + 9½O2 → 6CO2 + 7H2O 1

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4 Fig. 4.1 shows how propane, C3H8, can be converted to propanoic acid, CH3CH2COOH. reaction 1 reaction 2 reaction 3 C3H8 CH3CH2CH2Cl CH3CH2CH2OH CH3CH2COOH Fig. 4.1 (a) Reaction 1 in Fig. 4.1 takes place in the presence of sunlight. C3H8 + Cl 2 CH3CH2CH2Cl + HCl The reaction takes place via initiation, propagation and termination steps. (i) Name the mechanism shown by reaction 1. ..................................................................................................................................... [1] (ii) Complete the mechanism for reaction 1. Construct equations to describe the steps of the mechanism. initiation Cl → 2Cl• 2 propagation 1 .................................................................................................................... propagation 2 .................................................................................................................... termination ............................................................................................ CH3CH2CH2Cl [3] (iii) Reaction 1 is initiated by the bond fission of Cl 2. State the type of bond fission shown in the initiation step. ..................................................................................................................................... [1] (iv) Compound Q is a by-product of reaction 1. Q H Cl H H C C C Cl H H H Name Q. ..................................................................................................................................... [1] (v) The molecular formula of Q is C3H6Cl 2. Identify the types of structural isomerism and stereoisomerism that a molecule with molecular formula C3H6Cl 2 can show. type of structural isomerism .............................................................................................. type of stereoisomerism .................................................................................................... [2] (b) State the reagent and solvent required for reaction 2. ............................................................................................................................................. [1] (c) Reaction 3 takes place when CH3CH2CH2OH is heated under reflux with acidified potassium dichromate(VI) solution. (i) State the colour change that takes place in the reaction mixture. ..................................................................................................................................... [1] (ii) Construct an equation to represent reaction 3. Use [O] to represent an atom of oxygen from the oxidising agent. ..................................................................................................................................... [1] (d) CH3CH2COOH reacts with an unsaturated alcohol R to form unsaturated ester S. (i) State the type of reaction that forms S. ..................................................................................................................................... [1] (ii) The infrared spectrum of S is shown in Fig. 4.2. 100 transmittance / % 50 0 4000 3000 2000 1500 1000 500 wavenumber / cm−1 Fig. 4.2 Three absorptions in the infrared spectrum in Fig. 4.2 confirm that S is an ester and is unsaturated. • Write 1, 2 or 3 on Fig. 4.2 against each of these three absorptions. • Complete Table 4.1 to show which bond is responsible for each absorption that you have identified in Fig. 4.2. Table 4.1 absorption 1 2 3 bond responsible [3]

Mark scheme: 4(a)(i) free-radical substitution 1 4(a)(ii) M1 C3H8 + Cl● → CH3CH2CH2● + HCl 3 OR C3H8 + Cl● → C3H7● + HCl M2 CH3CH2CH2● + Cl2 → CH3CH2CH2Cl + Cl● OR C3H7● + Cl2 → C3H7Cl + Cl● etc M3 CH3CH2CH2● + Cl● → CH3CH2CH2Cl OR C3H7● + Cl● → CH3CH2CH2Cl 4(a)(iii) homolytic 1 4(a)(iv) 1,2-dichloropropane 1 4(a)(v) M1 (type of structural isomerism) positional 2 M2 (type of stereoisomerism) optical 4(b) sodium hydroxide AND water 1 4(c)(i) orange to green 1 4(c)(ii) CH3CH2CH2OH + 2[O] → CH3CH2COOH + H2O 1 4(d)(i) condensation 1 4(d)(ii) M1 absorption labelled at approx. 1750 cm–1 identified as C=O 3 M2 absorption labelled at approx. 1650 cm–1 identified as C=C M3 absorption labelled at approx. 1170 cm–1 identified as C—O 4(d)(iii) (0.31 / 4.7  100 / 1.1) = 6 carbon atoms 1

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