Cambridge A Level Chemistry 9701 — 2025 May/June Paper 2 · Variant 4

1 Elements in Period 3 of the Periodic Table show trends in their properties. (a) Complete Table 1.1 by identifying the lattice structures of the crystalline solids of Mg, Si and P. Table 1.1 element Mg Si P lattice structure in crystalline solid [3] (b) The relative electrical conductivities of the Period 3 elements are shown in Fig. 1.1. electrical conductivity Na Mg Al Si P S Cl Ar element Fig. 1.1 Explain why there is an increase in conductivity from Na to Al and why P, S and Cl are non‑conductors of electricity. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) The third ionisation energies of the Period 3 elements are shown in Fig. 1.2. third ionisation energy Na Mg Al Si P S Cl Ar element Fig. 1.2 (i) Write an equation, including state symbols, to represent the third ionisation energy of argon. ..................................................................................................................................... [2] (ii) The differences in the values for third ionisation energy shown in Fig. 1.2 are due to differences in the strength of attraction between the nucleus and the outer electron of each ion. State two factors that affect the strength of attraction between the nucleus and the outer electron. 1 ........................................................................................................................................ 2 ........................................................................................................................................ [2] (iii) Use Fig. 1.2 to suggest the most significant factor that determines the size of attraction between the nucleus and the outer electron. Explain your answer. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iv) In the third ionisation energy of argon, the ion produced has the electronic configuration 1s2 2s2 2p6 3s2 3p3. Complete Fig. 1.3 to show the arrangement of electrons in the orbitals of this ion. 1s 2s 2p 3s 3p Fig. 1.3 [1] (d) Most Period 3 elements react with oxygen to form oxides. (i) Write an equation for the reaction of phosphorus with oxygen. ..................................................................................................................................... [1] (ii) Write an equation for the reaction of aluminium oxide with an excess of aqueous sodium hydroxide. ..................................................................................................................................... [1] [Total: 14]

Mark scheme: Question Answer Marks 1(a) 3 Mg Si P M1 Giant metallic M2 Giant molecular M3 Simple molecular 1(b) M1 Na to Al have (delocalised) electrons that can move (through the structure / lattice) 2 AND (P / S / Cl) do not (have delocalised electrons / mobile charge carriers) M2 Na to Al increasing number of delocalised electrons 1(c)(i) Ar2+(g) → Ar3+(g) + e(–) 2 M1 a correct equation which represents an ionisation process e.g. Xn+ → X(n+1)+ + e(–) M2 correct equation to show third ionisation energy of Ar including (g) state symbols 1(c)(ii) M1 nuclear charge 2 M2 distance of outer electron(s) from nucleus OR ionic radius OR shielding (by inner shells and / or sub-shells) 1(c)(iii) M1 (most significant factor) = distance of outer electron(s) from nucleus OR ionic radius OR shielding OR shells 2 M2 (3rd IE) value for (Na and) Mg is (much) greater than Al (to Ar) OR (Na and) Mg has electron(s) removed from a shell that is closer to the nucleus / less shielding OR (Na and) Mg has electron(s) removed from a shell that is lower in energy 1(c)(iv) 1 1(d)(i) P4 + 5O2 → P4O10 1 1(d)(ii) Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4 1

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2 (a) Fig. 2.1 shows the covalent bonds and lone pairs of electrons in a molecule of SCl 2. Cl S Cl Fig. 2.1 (i) Use VSEPR theory to predict the shape of a molecule of SCl 2. ..................................................................................................................................... [1] (ii) Predict the bond angle in a molecule of SCl 2. ................... ° [1] (b) SCl is a red liquid that reacts with water. 2 2SCl 2(l) + 3H2O(l) H2SO3(aq) + S(s) + 4HCl (aq) (i) Describe two observations, other than temperature change, that are made when an excess of water is added to SCl 2. ........................................................................................................................................... ..................................................................................................................................... [2] (ii) When SCl reacts with water, the SCl is broken down and a disproportionation reaction 2 2 occurs. State the oxidation numbers of sulfur in SCl and 2 H2SO3. oxidation number of S in SCl ........................................................................................... 2 oxidation number of S in H2SO3 ........................................................................................ [2] (iii) State the general name to describe the type of reaction that occurs when a substance is broken down by water. ..................................................................................................................................... [1] [Total: 7]

Mark scheme: 2(a)(i) non-linear 1 2(a)(ii) 104.5° 1 2(b)(i) In any order: 2 M1 (solution / liquid) (red) to colourless M2 yellow solid appears 2(b)(ii) oxidation number of S in SCl 2 = (+) 2 / (+) II 2 oxidation number of S in H2SO3 = (+) 4 / (+) IV 2(b)(iii) hydrolysis 1

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3 H2(g) and I2(g) react to form HI(g) in a reversible reaction, as shown in equation 1. equation 1 H2(g) + I2(g) 2HI(g) In three separate experiments, a student combines different amounts of two or more of the gases from equation 1. In each experiment, the gases are left to reach equilibrium at a given temperature. (a) In experiment 1, H2(g) and I2(g) are combined. Water is then added to the equilibrium mixture to produce 1.00 dm3 of solution A. The amount of I2(aq) present in 1.00 dm3 of solution A is found by titration with Na2S2O3(aq). Exactly 32.90 cm3 of 0.200 mol dm–3 Na2S2O3 reacts with all of the I2 in a 25.0 cm3 sample of solution A. I2(aq) + 2S2O32–(aq) 2I–(aq) + S4O62–(aq) (i) Calculate the amount, in mol, of S2O32– that reacts in the titration. amount of S2O32– = .............................. mol [1] (ii) Use your answer to (a)(i) to calculate the amount, in mol, of I2 present in 1.00 dm3 of solution A. (If you were unable to obtain an answer in (a)(i), then use 9.42 × 10–3 mol. This is not the correct answer.) amount of I2 in 1.00 dm3 of solution A = .............................. mol [2] (b) In experiment 2, 0.100 mol of H2(g), 0.200 mol of I2(g) and 0.300 mol of HI(g) are combined. At equilibrium 0.154 mol of I2 is present. Calculate the amounts, in mol, of H2 and HI in the equilibrium mixture produced in experiment 2. amount of H2 in equilibrium mixture = .............................. mol amount of HI in equilibrium mixture = .............................. mol [3] (c) In experiment 3, 0.0772 mol of H2 and 0.0986 mol of I2 are present in an equilibrium mixture at 298 K. H2(g) + I2(g) 2HI(g) Kc = 7.94 × 102 Use the equilibrium constant, Kc, to calculate the amount, in mol, of HI present in the equilibrium mixture in experiment 3. amount of HI in equilibrium mixture = .............................. mol [1] (d) The value of Kc for the dissociation of HCl at 298 K is 5.50 × 10–34. 2HCl (g) H2(g) + Cl 2(g) Kc = 5.50 × 10–34 (i) Define covalent bond. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Describe and explain the relative thermal stabilities of the hydrogen halides HCl and HI. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iii) Use the data given in (c) and (d) to suggest a value for the equilibrium constant for the dissociation of HBr(g) at 298 K. ..................................................................................................................................... [1] [Total: 11]

Mark scheme: 3(a)(i) 0.00658(0) mol 1 3(a)(ii) M1 I2 in 25.0 cm3 0.00658 / 2 = 0.00329 (mol) 2 M2 0.00329 × 1000 / 25.0 = 0.132 (mol) alternative answer using 9.42 × 10–3: M1 0.00471 M2 0.1884 3(b) M1 0.2 – 0.154 = 0.046 (mol H2 and / or I2 reacts) 3 M2 mol H2 at equilibrium 0.1 – 0.046 = 0.054 M3 mol HI at equilibrium 0.3 + (0.046 × 2) = 0.392 3(c) 2.46 1 3(d)(i) (electrostatic) attraction between the nuclei (of two atoms) and a shared pair of electrons 1 3(d)(ii) M1 HCl is more stable 2 AND (because) Cl atom is smaller / less distance between electron pair and nucleus / shorter (H-X) bond length M2 (In HCl ) stronger attraction between nucleus and shared pair of electrons OR (In HCl ) (fewer shells of electrons so) less shielding OR (In HCl ) greater orbital overlap so stronger interaction 3(d)(iii) any value or range of values for Kc between 1 –3 5.50 × 10–34 < Kc < 1.26 × 10

More questions on Reacting masses and volumes (of solutions and gases)

4 The skeletal formula of E is shown in Fig. 4.1. E O O Fig. 4.1 (a) State the molecular formula of E. ............................................................................................................................................. [1] (b) Name E. ............................................................................................................................................. [1] (c) E is made when a carboxylic acid and an alcohol react together. (i) Name the type of reaction that takes place during this esterification reaction. ..................................................................................................................................... [1] (ii) Write an equation for the formation of E from a carboxylic acid and an alcohol. Use structural formulae to represent the organic species. ..................................................................................................................................... [1] (iii) State the systematic name of the alcohol used to make E. ..................................................................................................................................... [1] (d) F is an isomer of E. F reacts with HCl (aq) to produce G and H. G is a secondary alcohol. H is also produced when HCl (aq) is added to CH3CN. (i) Construct an equation for the acid hydrolysis of CH3CN with HCl (aq). ..................................................................................................................................... [1] (ii) Draw the displayed formula of G. [2] (iii) CH3OH is used to make CH3CN in a two‑step process, as shown in Fig. 4.2. step 1 step 2 CH3OH CH3Cl CH3CN Fig. 4.2 State the reagents and conditions required for steps 1 and 2. step 1 ................................................................................................................................ step 2 ................................................................................................................................ [3] [Total: 11]

Mark scheme: 4(a) C5H10O2 1 4(b) propyl ethanoate 1 4(c)(i) condensation 1 4(c)(ii) CH3COOH + CH3CH2CH2OH → CH3COOCH2CH2CH3 + H2O 1 4(c)(iii) propan-1-ol 1 4(d)(i) CH3CN + HCl + 2H2O → CH3COOH + NH4Cl 1 4(d)(ii) 2 4(d)(iii) M1 step 1 PCl 3 and heat 3 OR HCl (g) OR PCl 5 OR SOCl 2 OR NaCl / KCl and conc. H2SO4 / conc. H3PO4 M2 step 2 reagent KCN M3 conditions for step 2 dissolved in ethanol AND heat

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5 The skeletal formula of W is shown in Fig. 5.1. W Fig. 5.1 (a) W has two positional isomers. Only one shows stereoisomerism. Draw the structures of the two positional isomers of W in the boxes. [2] (b) (i) Describe the origin of stereoisomerism in W. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State why W shows stereoisomerism but one of the positional isomers in (a) does not. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (c) Draw the skeletal structure of the stereoisomer of W. [1] (d) W reacts with reagent X to produce ethanoic acid and pentanoic acid. (i) State the role of X in this reaction. ..................................................................................................................................... [1] (ii) Identify X and state the conditions used for this reaction. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 7]

Mark scheme: 5(a) M1 2 M2 OR 5(b)(i) no rotation / restricted rotation of C=C / pi bond 1 5(b)(ii) (W / it has two) different groups bonded to each C of the double bond 1 5(c) 1 5(d)(i) oxidising agent 1 5(d)(ii) hot concentrated acidified KMnO4 1

More questions on Isomerism: structural isomerism and stereoisomerism

6 P, Q and R are three different hydrocarbon molecules. (a) (i) Define empirical formula. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Hydrocarbon P contains 85.7% by mass of carbon. Calculate the empirical formula of P. Show your working. empirical formula of P = .............................. [2] (iii) Molecules of P have straight chains. Name the homologous series to which P belongs. ..................................................................................................................................... [1] (b) Q is a volatile hydrocarbon. 0.194 g of gaseous Q occupies a volume of 71.5 cm3 at 100 °C and 100 kPa. Use the ideal gas equation to calculate the Mr of Q. Mr of Q = .............................. [2] (c) The mass spectrum of hydrocarbon R is recorded. Information about the two peaks with m / e greater than 135 is shown in Fig. 6.1. 100 relative abundance 11.0 136 137 138 139 m / e Fig. 6.1 (i) Use Fig. 6.1 to deduce the number of carbon atoms in a molecule of R. Show your working. number of carbon atoms = .............................. [2] (ii) Use Fig. 6.1 and your answer to (c)(i) to deduce the molecular formula of R. ..................................................................................................................................... [1] (iii) Suggest the molecular formula of the fragment of R with m / e = 57. ..................................................................................................................................... [1] [Total: 10]

Mark scheme: 6(a)(i) simplest (whole number) ratio of atoms (of the elements) in a compound 1 6(a)(ii) C : H 2 85.7 14.3 M1 or 7.14 : or 14.3 12 1 1 : 2 M2 CH2 6(a)(iii) alkene(s) 1 6(b) M1 convert temp to 373 K (and use) 2 M2 correct rearrangement and use 7.15 = n8.31(4) × T to find n AND Mr = 0.194 / n Mr = 84.1 6(c)(i) 100 11 2 M1  1.1 100 M2 10 6(c)(ii) C10H18 1 6(c)(iii) (C4H9)+ 1

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