Cambridge A Level Chemistry 9701 — 2019 Feb/March Paper 2 · Variant 2

1 Nitrogen, N2, is the most abundant gas in the Earth’s atmosphere and is very unreactive. (a) State why N2 is very unreactive. .............................................................................................................................................. [1] (b) Magnesium and lithium both form nitrides with N2. These compounds both contain the N3– ion. (i) Write an equation for the reaction of magnesium with N2 to form magnesium nitride. ....................................................................................................................................... [1] (ii) Solid lithium nitride, Li3N, reacts with water according to the following equation. Li3N(s) + 3H2O(l) 3LiOH(aq) + NH3(aq) State one observation you would make during this reaction. ....................................................................................................................................... [1] (c) (i) State the industrial importance of ammonia. ....................................................................................................................................... [1] (ii) One method of producing NH3 is by heating ammonium chloride, NH4Cl, with CaO. 2NH4Cl + CaO 2NH3 + CaCl 2 + H2O Explain why the reaction of NH4Cl with CaO produces ammonia. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (d) Three oxides of nitrogen, NO, NO2 and N2O, can be formed under different conditions. (i) Complete the table to give the oxidation numbers of nitrogen in NO and NO2. compound NO NO2 oxidation number of N [1] (ii) NO2 can be formed by different chemical reactions. Write equations for the formation of NO2 by: ● the reaction of N2 with O2 ............................................................................................................................................. ● the thermal decomposition of magnesium nitrate. ............................................................................................................................................. [2] (iii) Molecules of N2O can be formed by the reaction between N2 and O2. The bond between the N and O atoms (N O) is a co-ordinate (dative covalent) bond. 2N2(g) + O2(g) 2N≡N O(g) The enthalpy change of reaction for this reaction is +82 kJ mol–1. Calculate the bond enthalpy, in kJ mol–1, of the N O bond. Use relevant data from the Data Booklet to answer this question. bond enthalpy of the N O bond = ............................. kJ mol–1 [2] (e) Nitrosyl chloride, NOCl, is a reactive gas that is sometimes formed when NO reacts with Cl 2. nitrosyl chloride O N δ+ Cl δ– NOCl is a strong electrophile and readily undergoes an addition reaction with alkenes. Complete the diagram to show the mechanism of the electrophilic addition reaction of NOCl with ethene. Include all necessary charges, lone pairs and curly arrows, and the structure of the organic intermediate. H H C C H H H H H C C H δ+ N Cl O N O Cl δ– [2] [Total: 13]

Mark scheme: 1(a) strong triple bond / strong N≡N OR high activation energy / Ea OR non-polar 1 1(b)(i) 3Mg + N2 → Mg3N2 1 1(b)(ii) solid disappears 1 1(c)(i) (it is used to make) fertilisers 1 1(c)(ii) M1 CaO displaces NH3 (from its salt / NH4+) M2 CaO is a stronger base / more basic (than NH3) 2 1(d)(i) NO NO2 (+)2 / (+)II (+)4 / (+)IV 1 1(d)(ii) M1 ½N2 + O2 → NO2 M2 Mg(NO3)2 → MgO + 2NO2 + ½O2 2 1(d)(iii) M1 +82 (= Eo=o – 2EN→O) = (+)496 – 2 × EN→O M2 EN→O = ½ × (496–82) = ½ × 414 = 207 (kJ mol–1) 2 Question Answer Marks 1(e) M1 curly arrow from C=C to Nδ+ AND curly arrow from N—Cl to Cl δ– M2 intermediate AND curly arrow from lone pair on Cl – to C(+) 2

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2 The elements in Group 17 of the Periodic Table are called the halogens. They form stable compounds with both metals and non-metals. The table gives some data about F2, HCl and CaF2. F2 HCl CaF2 boiling point / K 85 188 2773 relative formula mass 38.0 36.5 78.1 (a) (i) State what is meant by the term relative formula mass. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) F2 and HCl are both covalent molecules. Suggest why the boiling point of HCl is higher than that of F2. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iii) Explain why CaF2 has a very high boiling point. ............................................................................................................................................. ....................................................................................................................................... [1] (iv) CaF2(aq) can be made by the reaction of calcium carbonate with hydrofluoric acid, HF(aq). Write an equation for this reaction. Include state symbols. ....................................................................................................................................... [2] (b) (i) Complete the electronic configuration of a chloride ion. 1s2 ................................................................................................................................. [1] (ii) When Cl 2 is passed over hot iron, FeCl 3 is formed. However, when I2(g) is passed over hot iron, the following reaction occurs. Fe(s) + I2(g) FeI2(s) State what you would observe during the reaction between Fe and I2. Explain why FeI2(s) is formed rather than FeI3(s). observation .......................................................................................................................... ............................................................................................................................................. explanation .......................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. [2] (iii) FeI2 is soluble in water. A student carries out a chemical test to confirm that a solution of FeI2 contains aqueous iodide ions, I–(aq). The student adds a single reagent and a precipitate forms. Identify the reagent the student uses. State the colour of the precipitate that forms. reagent ................................................................................................................................ colour of precipitate ............................................................................................................. [2] (iv) Compounds containing I– are often contaminated by bromide ions, Br –. Identify a further reagent that the student could use to show that the precipitate formed in (iii) contained iodide ions. ....................................................................................................................................... [1] (c) HOF is the only known molecule that contains only the elements hydrogen, oxygen and fluorine. (i) Draw a ‘dot-and-cross’ diagram to represent the bonding in a molecule of HOF. Show the outer shell electrons only. [2] (ii) HOF can be made by the reaction of F2 with ice at – 40 °C. The reaction is similar to the reaction of Cl 2 with cold water. Suggest an equation for the reaction of F2 with ice. ....................................................................................................................................... [1] (iii) HOF is an unstable compound and decomposes to form HF and O2. HOF → HF + 12 O2 ΔH = –139 kJ mol–1 Draw a fully labelled reaction pathway diagram on the axes provided to show the decomposition of HOF into HF and O2. enthalpy progress of reaction [2] (iv) Pure HF is a colourless liquid at 273 K. The liquid contains HF molecules that have strong hydrogen bonds between them. Draw a fully labelled diagram to suggest how a hydrogen bond can form between two HF molecules. [3] (d) Interhalogen compounds, such as BrCl or IF5, contain two or more different halogen atoms that are covalently bonded. D is an interhalogen compound that contains only chlorine and fluorine. At 0 °C and 101 325 Pa, 1 dm3 of D has a mass of 4.13 g. (i) Use the general gas equation to calculate the relative molecular mass, Mr, of D. Mr = .............................. [3] (ii) Use your answer to (i) to determine the molecular formula of D. If you were unable to calculate the Mr in (i), assume that the Mr is 130.5. This is not the correct value. molecular formula of D = .............................. [1] [Total: 25] Question 3 starts on the next page.

Mark scheme: 2(a)(i) M1 c mass of a molecule OR d (weighted) average / mean mass of the molecules OR e mass of one mole of molecules M2 c / d compared to 1 12 (the mass) of an atom of carbon-12 OR on a scale in which a carbon-12 atom / isotope has a mass of (exactly) 12 (units) e relative / compared to 1 12 (the mass) of 1 mole of carbon-12 OR on a scale in which 1 mole of carbon-12 (atoms / isotope) has a mass of (exactly) 12 g 2 Question Answer Marks 2(a)(ii) M1 identification of the IMF between F2 molecules and between HCl molecules HCl has (permanent) dipoles and / or induced dipoles F2 has induced dipoles M2 comparison of strength of IMF’s in F2 and HCl Intermolecular forces in HCl are stronger than F2 2 2(a)(iii) strong (electrostatic) forces of attraction between (oppositely charged) ions 1 2(a)(iv) CaCO3(s) + 2HF(aq) → CaF2(aq) + CO2(g) + H2O(l) M1 species and balancing M2 state symbols 2 2(b)(i) 1s2 2s2 2p6 3s2 3p6 1 2(b)(ii) M1 purple gas / vapour disappears M2 iodine is not a strong enough oxidising agent ORA 2 2(b)(iii) M1 silver nitrate / AgNO3 M2 yellow 2 2(b)(iv) (aqueous) ammonia / NH3(aq) / ammonium hydroxide / NH4OH(aq) 1 2(c)(i) M1 bonding pairs correct M2 rest of molecule, incl. lone pairs. 2 2(c)(ii) F2 + H2O → HF + HOF 1 H O F Question Answer Marks 2(c)(iii) M1 labelled reactants AND products lower on right M2 labelled enthalpy change with correct arrow 2 2(c)(iv) M1 H-bond labelled / shown as distinct from H—F bond M2 correct sequence of three correct dipoles M3 lone pair on F in line with H-bond 3 2(d)(i) pV 101 325 0.001 pV = nRT n = = = 0.0447 mol RT 8.31 273 ∴ × × r m 4.13 M = = = 92.4 or 92.5 n 0.0447 ∴ M1 Use of T = 273 K, V = 0.001 m3 and p = 101325 Pa M2 correct use of pV = nRT using values from M1 M3 correct calculation of Mr using 4.13 ÷ moles from M2 3 2(d)(ii) Cl F3 1

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3 P, Q and R all contain five carbon atoms. P Q R OH O OHC H H3C C C N C C C H3C CH2CH2CH3 CH2CH3 H CH2CH3 A student carries out several tests to distinguish between P, Q and R. (a) Complete the table, identifying any observations for the reaction of each reagent with P, Q and R. If no reaction occurs, write ‘no reaction’. observations with reagent P Q R Na(s) 2,4-DNPH no reaction acidified K2Cr2O7(aq) no reaction [3] (b) Q is reduced by NaBH4. Write an equation for the reaction of Q with NaBH4. In your answer, use [H] to represent NaBH4. C5H10O + ............................................................................................................................. [1] (c) R exists as a pair of stereoisomers. Identify the type of stereoisomerism shown by R and draw the structure of the other stereoisomer. type of stereoisomerism ................................................. stereoisomer of R [2] (d) The infra-red spectrum shown corresponds to one of P, Q or R. 100 transmittance 50 0 4000 3000 2000 1500 1000 500 wavenumber / cm–1 Deduce which of the compounds, P, Q or R, produces this spectrum. Explain your reasoning. In your answer, identify any relevant absorptions in the infra-red spectrum and the bonds that correspond to these absorptions in the region above 1500 cm–1. compound ........................ explanation ................................................................................................................................. .................................................................................................................................................... .................................................................................................................................................... [3] [Total: 9]

Mark scheme: 3(e) P Q R Na(s) effervescence no reaction no reaction 2,4-DNPH no reaction orange ppt orange ppt acidified K2Cr2O7(aq) no reaction no reaction (turns) green 3 3(b) C5H10O + 2[H] → C5H12O 1 3(c) M1 geometric(al) M2 2 3(d) M1 compound P M2 (absorption at) 2250 cm–1 AND C≡N (stretch) M3 (absorption at) 3100–3700 cm–1 AND O—H (stretch) 3

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4 Allyl chloride is an important chemical used in the manufacture of plastics, pharmaceuticals and pesticides. allyl chloride Cl (a) Give the systematic name of allyl chloride. .............................................................................................................................................. [1] (b) Allyl chloride can be produced by many different methods. The most common method is chlorination of propene which proceeds via a free-radical substitution mechanism. Cl 2 Cl (i) The initiation step in this reaction is the formation of chlorine radicals (Cl ●) from Cl 2 molecules. State the conditions required to initiate this reaction. ....................................................................................................................................... [1] (ii) The propenyl radical, CH2=CHCH2●, is formed in the first propagation step of the reaction. Write an equation to show the formation of CH2=CHCH2● in this propagation step. ....................................................................................................................................... [1] (iii) Explain why the free-radical substitution reaction gives a low yield of allyl chloride. ............................................................................................................................................. ....................................................................................................................................... [1] (iv) Allyl chloride can also be formed by the following substitution reaction. reagent X OH Cl Suggest the identity of reagent X. ....................................................................................................................................... [1] (c) A series of reactions starting from allyl chloride is shown. OH reaction 1 Cl HO Cl reaction 2 Y CH3COO CH3COO reaction 3 CH3COO Cl CH3COO CN HCN and NaCN (i) Suggest a reagent that can be used in reaction 1. ....................................................................................................................................... [1] (ii) In reaction 2, the organic product of reaction 1 is mixed with concentrated H2SO4 and an organic acid, and then heated under reflux. State the role of the concentrated H2SO4. Identify the organic acid used. role of the concentrated H2SO4 ........................................................................................... identity of the organic acid .................................................................................................. [2] (iii) State the name of the mechanism that occurs in reaction 3. ....................................................................................................................................... [1] (iv) The organic product of reaction 3 is Y. Y can be hydrolysed using excess aqueous H2SO4 to form Z. The molecular formula of Z is C4H8O4. Draw the structure of Z. [2] (d) 2-bromo-1-chloropropane, CH3CHBrCH2Cl, is the major product of the reaction of allyl chloride with HBr. major product minor product Br HBr Cl Cl Br Cl and Explain why 2-bromo-1-chloropropane is the major product of this reaction. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] [Total: 13]

Mark scheme: 4(a) 3-chloroprop-1-ene 1 4(b)(i) ultra-violet (light) / sun(light) 1 4(b)(ii) CH2=CHCH3 + Cl ● → CH2=CHCH2● + HCl OR C3H6 + Cl ● → C3H5● + HCl 1 Question Answer Marks 4(b)(iii) free-radical (substitution) reactions are uncontrolled OR further chlorination / substitution occurs 1 4(b)(iv) SOCl 2 OR PCl 5 OR PCl 3 OR c(oncentrated) HCl 1 4(c)(i) cold, dilute acidified KMnO4 / potassium manganate(VII) 1 4(c)(ii) M1 catalyst M2 ethanoic acid / CH3CO2H 2 4(c)(iii) nucleophilic substitution / SN2 1 4(c)(iv) M1 hydrolysed nitrile on straight-chain 4C backbone M2 3,4-diol 2 4(d) M1 major product formed from more stable intermediate / carbocation OR (intermediate has) 2°carbocation which is (more) stable M2 (positive) inductive effect / (+)I of alkyl groups (on the intermediate) 2

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