Cambridge A Level Chemistry 9701 — 2021 Oct/Nov Paper 2 · Variant 2

1 Hydrogen iodide, HI, is a colourless gas at room temperature. (a) (i) Explain why HI has a higher boiling point than HCl and HBr. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) The bar chart shows the boiling points of HCl, HBr and HI. The boiling point of HF is not shown. 300 280 260 240 boiling point / K 220 200 180 160 HF HCl HBr HI Hydrogen bonds form between HF molecules. Draw a bar on the bar chart to predict the boiling point of HF. Explain your answer. ............................................................................................................................................. ....................................................................................................................................... [2] (b) The standard enthalpy change of formation, , of HI(g) is +26.5 kJ mol–1. Define the term standard enthalpy change of formation. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (c) HI(g) can be formed by reacting H2(g) with I2(g). The reaction is reversible, and an equilibrium forms quickly at high temperatures. H2(g) + I2(g) 2HI(g) (i) Construct an expression for the equilibrium constant, Kp, for the reaction of H2(g) and I2(g) to form HI(g). Kp = [1] (ii) The equilibrium partial pressures of the gases at 200 °C are as follows. pH2(g) = 895 Pa pI2(g) = 895 Pa pHI(g) = 4800 Pa Calculate Kp for this reaction. Kp = .............................. [1] (iii) State how the value of Kp would change, if at all, if the reaction were carried out at 100 °C rather than 200 °C. Explain your answer. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (d) HI reacts with oxygen to form iodine and water. (i) Construct an equation for the reaction of HI with oxygen. ....................................................................................................................................... [1] (ii) Explain, with reference to oxidation numbers, why this reaction is a redox reaction. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (e) HI(g) can also be formed by the reaction of I2(g) with hydrazine, N2H4(g). 2I2(g) + N2H4(g) → 4HI(g) + N2(g) State the change in pressure that would occur when 2 mol I2(g) fully reacts with 1 mol N2H4(g) in a sealed container at constant temperature. Explain your answer. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (f) In the laboratory, HI(aq) can be formed in a two-step process. step 1 3I2(s) + 2P(s) → 2PI3(s) step 2 PI3(s) + 3H2O(l) → H3PO3(aq) + 3HI(aq) (i) Draw a ‘dot-and-cross’ diagram of a PI3 molecule. [2] (ii) Name the type of reaction in step 2. ....................................................................................................................................... [1] (iii) H3PO3(aq) and HI(aq) are both strong Brønsted–Lowry acids. Give the meaning of the term strong Brønsted–Lowry acid. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iv) Give the formula of the conjugate base of H3PO3. ....................................................................................................................................... [1] (g) HI(g) reacts with propene, CH3CH=CH2(g) to form a mixture of 1-iodopropane and 2-iodopropane. (i) Identify which of 1-iodopropane and 2-iodopropane is the major product of this reaction. Explain your answer. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Complete the diagram to show the mechanism of the reaction between HI and CH3CH=CH2 that forms the major product identified in (g)(i). Include curly arrows, lone pairs of electrons and charges as necessary. H3C H C C H H H I + – [3] [Total: 26]

Mark scheme: 1(a)(i) M2 greater induced dipoles (between molecules) 2 1(a)(ii) M1 bar at HF shows any boiling point above HI on graph M2 explanation of difference in boiling point of a sample of HF in terms of strength (sum of) hydrogen bonds (and induced dipoles in HF) are stronger than (sum of) induced dipoles (and permanent dipoles in HCl / HBr / HI) 2 1(b) (enthalpy / energy change) when one mole of a compound is formed from its elements in their standard states 2 1(c)(i) 𝐾௣= 𝑝HIଶ 𝑝Hଶ 𝑝 Iଶ 1 1(c)(ii) 28.76 OR 28.8 OR 29 1 1(c)(iii) EITHER option 1 which assumes ∆Hreaction is (still) endothermic (using the value shown in (b)). M1 (Kp) decreases AND endothermic / ∆H(f) = + / positive M2 reaction favours formation of reactants / hydrogen and iodine OR (product) yield / partial pressure of HI decreases / equilibrium shifts to the left OR option 2 which realises that ∆Hreaction is in fact exothermic (using bond energy data in Data Booklet) M1 (Kp) increases AND exothermic / ∆H(f) = + / negative M2 reaction favours formation of products / hydrogen iodide yield increases / partial pressure of HI increases / equilibrium shifts to the right 2 1(d)(i) 4HI + O2 → 2I2 + 2H2O 1 Question Answer Marks 1(d)(ii) M1 I / iodine (increases) oxidation number –1 → 0 so oxidation / is oxidised OR HI / is oxidised as I (increases) oxidation number –1 → 0 M2 O (decreases) oxidation number 0 → –2 so reduction / is reduced 2 1(e) M1 pressure increases M2 (pressure goes up as) number of moles/molecules increases in ratio 3 (gas) reactants to 5 (gas) products OR pressure is (directly) proportional to number of moles/molecules 2 1(f)(i) M1 correct bonding pairs M2 correct number of remaining outer electrons on each atom 2 1(f)(ii) hydrolysis 1 1(f)(iii) proton donor / H+ donor fully dissociates / fully ionises 2 1(f)(iv) H2PO3– 1 1(g)(i) M1 2-iodopropane – formed from a (more) stable (secondary) (carbo)cation/intermediate M2 (because of) greater (positive) inductive effect / (+)I of two alkyl groups OR (because of positive) inductive effect / (+)I of more R / more methyl / more alkyl groups 2 Question Answer Marks 1(g)(ii) M1 curly arrow from = of C=C to H AND curly arrow from bond of H—I to I M2 curly arrow from lone pair of I– to C(+) of their intermediate M3 correct carbocation AND product for 2-iodopropane 3

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2 (a) Table 1 gives physical data for some of the Period 3 elements. Table 1 atomic number, Z 11 12 13 14 15 16 17 bonding present in element M C first ionisation energy / kJ mol–1 494 736 577 786 1060 1000 1260 maximum oxidation number +7 anionic radius / nm – – – 0.271 0.212 0.184 0.181 (i) Complete the row in the table labelled ‘bonding present in element’. Use C = covalent, I = ionic, M = metallic, as appropriate. [1] (ii) Explain the difference between the first ionisation energies of the elements with atomic numbers 11 and 17. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iii) Explain the difference between the first ionisation energies of the elements with atomic numbers 15 and 16. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iv) Complete the row in the table labelled ‘maximum oxidation number’. [1] (v) Explain the variation in anionic radius for the elements with atomic numbers 14 to 17. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (b) Use the axes to sketch a graph that shows the trend in melting points of the elements with atomic numbers 11 to 17. melting point of element 11 12 13 14 15 16 17 atomic number, Z [2] (c) Dmitri Mendeleev published the first Periodic Table in 1869. Mendeleev used his knowledge of chemical periodicity to propose the properties of gallium, 31Ga, a Group 13 element. Table 2 gives some chemical and physical data of elements in Group 13. Table 2 density boiling point cationic radius element / g cm–3 / K / nm 5B 2.34 3930 0.020 13Al 2470 0.050 31Ga 5.91 2400 49In 7.30 0.081 81Tl 11.8 1460 0.095 Complete the table by predicting values for the missing data. [3] (d) Indium and aluminium are elements in Group 13 of the Periodic Table. Indium has very similar chemical properties to aluminium. ● Indium reacts vigorously with hydrochloric acid to form a colourless gas and a salt in solution. ● Indium oxide, In2O3, is amphoteric. ● Gaseous indium bromide has the formula In2Br6. This molecule contains coordinate bonds. (i) Identify the formula of the salt formed when indium reacts with hydrochloric acid. ....................................................................................................................................... [1] (ii) Construct an equation for the reaction of In2O3 with excess aqueous NaOH. ....................................................................................................................................... [1] (iii) Draw a diagram that clearly shows the types of bond present in In2Br6(g). [2] [Total: 17]

Mark scheme: 2(a)(i) M M M C C C C 1 2(a)(ii) All 3 points correct scores two marks Any 2 points scores one mark • nuclear charge increases OR increasing proton number e.g. 17 / Cl has a greater nuclear charge • describe the similarity in shielding between the two elements e.g. they have almost the same shielding • describe the overall effect in terms of greater nuclear attraction for (outer) electrons e.g. (outer) electrons are attracted more (strongly) to the nucleus 2 2(a)(iii) M1 describes the difference between 1st IE of elements 15 and 16 (P and S) in terms of either: spin-pair repulsion (in element 16 / S) OR electron pair repulsion (in element 16 / S) M2 describes the location of the electron pair in the (3)p orbital which repel each other 2 2(a)(iv) (+)1 (+)2 (+)3 (+)4 (+)5 (+)6 1 2(a)(v) M1 (anions have) same number of electrons (but increasing proton number) M2 increasing proton number / nuclear charge AND increasing attraction of nucleus for (outer) electrons OR (outer) electrons attracted more (strongly) to the nucleus AND because of increasing proton number / nuclear charge 2 2(b) 2 Question Answer Marks 2(c) M1 density of 13Al: value within range 2.5–5.0 (g cm–3) M2 cationic radius of 31Ga: value within range 0.055–0.075 (nm) M3 boiling point of 49In: value within range 1500–2300 (K) 3 2(d)(i) InCl3 1 2(d)(ii) In2O3 + 2NaOH + 3H2O → 2NaIn(OH)4 1 2(d)(iii) M1 correct connectivity of In2Br6 M2 showing the two correct dative covalent bonds 2

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3 Compound T is an isomer of C6H12. T (a) Name T. .............................................................................................................................................. [1] (b) Draw the skeletal formula of a structural isomer of T that shows cis-trans (geometrical) isomerism. [1] (c) Each carbon atom in T forms a sigma (σ) bond to at least one other carbon atom, as shown. H3C CH3 C C H3C CH3 (i) n the diagram, draw the orbitals that represent the pi (π) bond that is also present in T. [1] (ii) State the hybridisation of the two carbon atoms between which the pi (π) bond forms. ....................................................................................................................................... [1] (d) A reaction scheme starting with T is shown. Reaction 2 occurs in the presence of a catalyst; knowledge of the mechanism for this reaction is not required. T U V HO OH reaction 1 reaction 2 O catalyst (i) Give the reagent(s) and conditions for reaction 1. ....................................................................................................................................... [1] (ii) State and explain how 2,4-dinitrophenylhydrazine (2,4-DNPH) can be used to detect the presence of V as a product of reaction 2. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iii) The progress of reaction 2 can be monitored by infrared spectroscopy. The absorption caused by O–H bonds is always present because water is used as a solvent. Identify two absorptions, and the bonds responsible for these absorptions, whose appearance will change significantly during the reaction. 1 .......................................................................................................................................... ............................................................................................................................................. 2 .......................................................................................................................................... ............................................................................................................................................. [2] (e) V is used in a wide range of organic reactions. Some reactions of V are shown. V W reaction 3 O O alkaline aqueous I2 O– reaction 4 NaBH4 X Y reaction 5 reaction 6 OH Z dehydration addition polymerisation (i) V and W are colourless and soluble in water. State what you would observe in reaction 3. ....................................................................................................................................... [1] (ii) Reaction 3 is a redox reaction. Identify which of the reactants is reduced in this reaction. ....................................................................................................................................... [1] (iii) Construct an equation for reaction 4. Use [H] in the equation to represent an atom of hydrogen from NaBH4. C6H12O + ��������������������������������������������������������������������������������������������������������������������� [1] (iv) X is a mixture of two optical isomers. Draw the two optical isomers in the boxes provided. [2] (v) Both optical isomers of X can be dehydrated to form a single product, Y. Give the reagent(s) and conditions required for reaction 5. ....................................................................................................................................... [1] (vi) Y can form an addition polymer Z. Draw one repeat unit of Z. [1] (vii) Reaction 6 does not proceed quickly at room temperature. Suggest why this is the case. ............................................................................................................................................. ....................................................................................................................................... [1] [Total: 17]

Mark scheme: 3(a) (2,3-)dimethylbut-2-ene 1 3(b) OR OR OR 1 3(c)(i) 1 3(c)(ii) sp2 1 3(d)(i) cold dilute acidified potassium manganate(VII) 1 3(d)(ii) M1 (2,4-DNPH will produce a) red / orange / yellow precipitate M2 V has a carbonyl group 2 3(d)(iii) M1 C—O in range 1040–1300 (cm–1) M2 C=O in range 1670–1740 (cm–1) 2 3(e)(i) yellow precipitate 1 3(e)(ii) Iodine / I2 1 3(e)(iii) C6H12O + 2[H] → C6H14O 1 Question Answer Marks 3(e)(iv) Draw two optical isomers of X. eg OR M1 One correct 3-dimensional representation of X M2 3-d structure which represents the enantiomer of their X 1 1 3(e)(v) heat AND concentrated H2SO4 / concentrated H3PO4 / concentrated sulfuric [(VI)] acid / concentrated phosphoric[(V)] acid 1 3(e)(vi) OR 1 3(e)(vii) high activation energy 1

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