Cambridge A Level Chemistry 9701 — 2018 Oct/Nov Paper 2 · Variant 1

1 Iron pyrite, FeS2, has a yellow colour that makes it look like gold metal. The compound contains the ions Fe2+ and S22–. (a) (i) Give the full electronic configuration of Fe2+. 1s2 ................................................................................................................................. [1] (ii) Calculate the oxidation number of sulfur in the S22– ion. Assume that each sulfur atom in the ion has the same oxidation number. oxidation number of sulfur in the S22– ion = .............................. [1] (b) Describe the metallic bonding in gold. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (c) Iron pyrite is often called fool’s gold because of its appearance. Impure samples of iron pyrite often contain a small amount of gold. The gold can be obtained from impure iron pyrite. The impure iron pyrite is roasted in oxygen, to produce iron(III) oxide and sulfur dioxide. Gold does not react with oxygen. (i) The sulfur dioxide produced during roasting would cause environmental consequences if released into the atmosphere. State and explain one of these environmental consequences. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iii) A sample of impure iron pyrite was roasted in oxygen. The composition of the mixture of solid products is shown. solid product mass / g Fe2O3 33.18 Au 0.37 Calculate the mass of FeS2 present in the sample of impure iron pyrite. Assume that all the FeS2 was converted to Fe2O3 during the roasting process. (Mr: FeS2, 120.0; Fe2O3, 159.6) mass of FeS2 = .............................. g [2] (iv) Use your answer to (iii) to calculate the percentage by mass of gold in this sample of impure iron pyrite. Assume that gold is the only impurity in this sample of impure iron pyrite. Give your answer to two significant figures. (If you were unable to calculate an answer to (iii), use 55.00 g as the mass of FeS2 in this calculation. This is not the correct answer.) percentage by mass of gold = .............................. % [1] [Total: 11]

Mark scheme: 1(a)(i) 1 1(a)(ii) –1 1 1(b) M1 attraction/hold M2 positive ions / cations AND delocalised electrons (may be seen in a labelled diagram) 2 1(c)(i) M1 acid rain M2 • destroys / damages / weathers / erodes / buildings / statues • kills/harms fish / coral / plants / crops / trees / deforestation • leaches salts / ions (aluminium) from soil (into rivers / lakes) • leaches away soil nutrients • breathing difficulties • lowers pH / increases acidity of soil / rivers / oceans / seas 2 1(c)(ii) balanced equation with 11O2 and 8SO2 M1: O2 and SO2 M2: 11 and 8 2 1(c)(iii) M1 is for process of calculating number of moles of Fe2O3 33.18 ÷ 159.6 (= 0.2079 mol) M2 for correct use of stoichiometry and 120.0 with candidate’s M1 M2 (0.2079) × 4 / 2 × 120.0 = 49.89 (g) 2 1(c)(iv) (0.37/(0.37+49.89)) = 0.74 1 Que estion Answer Ma arks

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2 (a) Nitrogen, N2, is an inert gas that makes up 78% of the Earth’s atmosphere. (i) Explain why nitrogen is inert. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Draw a ‘dot-and-cross’ diagram of a nitrogen molecule. Show outer electrons only. [1] (b) Nitrogen, N2, and oxygen, O2, react together in the air during lightning strikes to form nitrogen monoxide, NO. (i) Explain why the reaction of N2 and O2 occurs during lightning strikes. ............................................................................................................................................. ....................................................................................................................................... [1] (ii) Write two equations to suggest how the NO formed reacts further to create nitric acid, HNO3. 1 .......................................................................................................................................... 2 .......................................................................................................................................... [2] (c) Nitrate fertilisers are used to provide nitrogen for plant growth. Uncontrolled use of these can cause a reduction in animal and plant life in natural water supplies. Explain how uncontrolled use of nitrate fertilisers can cause this problem. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] (d) Some soils have compounds such as ammonium nitrate, calcium carbonate and calcium hydroxide added to them. (i) Suggest why calcium hydroxide is added to some soils. ....................................................................................................................................... [1] (ii) When calcium hydroxide reacts with compounds containing the ammonium ion, NH4+, a gas is produced. State the identity of this gas and explain why the reaction occurs. gas ...................................................................................................................................... explanation .......................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. [2] (iii) Another fertiliser, calcium ammonium nitrate, is formed when solid calcium carbonate is added to a mixture of aqueous ammonium nitrate and dilute nitric acid. Suggest what would be observed in this reaction. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iv) Calcium nitrate decomposes at a higher temperature than calcium ammonium nitrate. Write an equation for the thermal decomposition of calcium nitrate. ....................................................................................................................................... [1] [Total: 15]

Mark scheme: 2 2( 2 2( 2 2 2( (a)(i) 1 mark • trip • no • ne (a)(ii) 6 e– be (b)(i) (lightn (b)(ii) M1 NO M2 2N 2(c) M1 fertilise OR fertilise M2 alg AND sunligh AND bacter M3 dro (d)(i) to incre (d)(ii) M1 am M2 dis k for each bullet ple bond on-polar / no dipo eeds a lot of ene etween atoms A ing) provides the O + ½ O2 → NO NO2 + H2O + ½ er / nitrates disso er / nitrates are w gal bloom / prom ht is blocked out ria break down o op in oxygen (co ease / raise pH mmonia / NH3 splaces NH3 , max 2 ole rgy to break / str AND two electron e (high) activatio O2 ½ O2 → 2HNO3 olve in (river / gro washed / leache ote algal growth t (preventing pho or decay dead o oncentration) rong ns on each N ato on energy ound water) ed out / flows int h / explosion of p otosynthesis) / p rganisms / plants om to (river/groundw plant growth plants can no lon s / algae water) nger carry out ph hotosynthesis (a and die) 2 1 1 2 3 1 2 Question Answer Marks 2(d)(iii) M1 effervescence / fizzing / bubbling M2 solid disappears 2 2(d)(iv) 2Ca(NO3)2 → 2CaO + 4NO2 + O2 1

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3 Trihalomethanes are organic molecules in which three of the hydrogen atoms of methane are replaced by halogen atoms, for example CHCl 3. (a) CHCl 3 is a colourless liquid with a high vapour pressure. (i) Explain what is meant by high vapour pressure. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) An important reaction of CHCl 3(g) is the manufacture of CHCl F2(g), using the following reversible reaction. CHCl 3(g) + 2HF(g) CHCl F2(g) + 2HCl (g) Use the data to calculate the enthalpy change of reaction, ΔHr , for the formation of CHCl F2(g) as shown in the equation. enthalpy change of compound formation, ΔHf / kJ mol–1 CHCl 3(g) –103.2 CHCl F2(g) – 482.2 HF(g) –273.3 HCl (g) –92.3 enthalpy change of reaction, ΔHr = .............................. kJ mol–1 [3] (iii) The reaction in (ii) is carried out using a heterogeneous catalyst. Explain fully the meaning of the terms heterogeneous and catalyst. heterogeneous .................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. catalyst ................................................................................................................................ ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. [3] (b) CHCl F2 was used as an alternative to chlorofluorocarbons (CFCs). CHCl F2 should no longer be used because it was found to contribute to the enhanced greenhouse effect. (i) Give the meaning of the term enhanced greenhouse effect. ............................................................................................................................................. ....................................................................................................................................... [1] (ii) Explain how CHCl F2(g) may contribute to this effect. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iii) Suggest another environmental problem associated with the use of CHCl F2. ....................................................................................................................................... [1] (c) CHCl F2 is also used to produce the monomer tetrafluoroethene, C2F4. This monomer can be used to produce poly(tetrafluoroethene), PTFE. (i) State the type of polymerisation that occurs during the production of PTFE. ....................................................................................................................................... [1] (ii) Draw the repeat unit of PTFE. [1] (iii) Suggest why PTFE is used as a coating for cooking pans. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [1] (iv) Waste disposal can cause litter problems. State two other difficulties associated with the disposal of PTFE. 1 .......................................................................................................................................... ............................................................................................................................................. 2 .......................................................................................................................................... ............................................................................................................................................. [2] [Total: 17] Question 4 starts on the next page.

Mark scheme: 3(a)(i) M1 gas / vapour (particles / molecules) in equilibrium (with liquid / solid) M2 greater proportion of gas (particles) than liquid (particles) (in comparison to a liquid of lower vapour pressure) 2 3(a)(ii) –17.(0) (kJ mol–1) 999 M1 ∆Hr = x(–482.2) + y(–92.3) – v(–103.2) – w(–273.3) where x y v and w are integers ⩾1 (ignore stoichiometry) M2 use of correct stoichiometry where x = 1 y = 2 v = 1 and w = 2 3 3(a)(iii) M1 in a different phase / state from reactants M2 a substance that speeds up a (chemical) reaction M3 catalyst is regenerated / not used up / undergoes temporary chemical change / recovered unchanged 3 3(b)(i) Human activity creates / additional / more/increase / thicker layer in greenhouse gas(es) / CHCl F2 OR Human activity has an impact on climate change / temperature at earth’s surface / temperature of sea 1 3(b)(ii) M1 traps (more)heat M2 (in the atmosphere leading to) greater global warming or wtte 2 3(b)(iii) ozone depletion / thinning 1 3(c)(i) addition 1 Question Answer Marks 3(c)(ii) 1 3(c)(iii) molecule unreactive / inert 1 3(c)(iv) non-biodegradable creates toxic / harmful gases / HF / CO2 / CO if burnt 2

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4 The structure of glycolic acid is shown. H O H C C OH OH glycolic acid (a) Complete the table to show what you would observe when an aqueous solution of glycolic acid is added separately to each of the reagents. If a reaction occurs, state the functional group of glycolic acid that is responsible for the reaction. does a reagent observation with glycolic acid reaction functional group occur? / Na2CO3(aq) 2,4-DNPH acidified Cr2O72– [4] (b) Two reaction sequences to make glycolic acid are shown. HCN and NaCN sequence A HCHO X CH2(OH)CO2H reaction 1 reaction 2 Br2 sequence B CH3CO2H CH2BrCO2H CH2(OH)CO2H reaction 3 reaction 4 (i) Draw the structure of X. [1] (ii) Name the reagent for reaction 2. ....................................................................................................................................... [1] (iii) Name the mechanism of reaction 3. ....................................................................................................................................... [1] (iv) Suggest the essential condition for reaction 3. ....................................................................................................................................... [1] (v) Reaction 4 occurs via an SN2 mechanism. Complete the diagram for the mechanism for reaction 4. Include all relevant charges, partial charges, curly arrows and lone pairs. H O H O H C C OH H C C OH Br OH –OH [2] (c) Glycolic acid can also be made by reacting glyoxylic acid with NaBH4. H O H O NaBH4 C C H C C OH O OH OH glyoxylic acid glycolic acid (i) State the role of NaBH4 in this reaction. ....................................................................................................................................... [1] (ii) Write an equation for this reaction using molecular formulae. Use [H] to represent NaBH4. ....................................................................................................................................... [2] (d) When glycolic acid is heated in the presence of a sulfuric acid catalyst, a new compound, Y, C4H4O4, is formed. The equation for the reaction is given. 2CH2(OH)CO2H C4H4O4 + 2H2O glycolic acid Y (i) The infra-red spectrum of Y is shown. 100 transmittance 50 0 4000 3000 2000 1500 1000 500 wavenumber / cm–1 State how this spectrum differs from an infra-red spectrum of glycolic acid. Explain your answer with particular reference to the peaks within the range 1500 – 4000 cm–1. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Suggest a structure for Y. [2] [Total: 17]

Mark scheme: 4(a) reagent observation with glycolic acid does a reaction occur? 9 / × functional group Na2CO3(aq) effervescence / fizzing / bubbling 9 COOH / carboxylic acid 2,4–DNPH no visible reaction owtte × (no group required) acidified Cr2O7 2- orange to green 9 –OH / alcohol 1 mark for each in column 2 (obs) 1 mark for COOH and OH 4 Question Answer Marks 4(b)(i) 1 4(b)(ii) hydrochloric / sulfuric / nitric / phosphoric acid 1 4(b)(iii) free-radical substitution 1 4(b)(iv) UV (light) / sunlight 1 4(b)(v) M1 lone pair on –OH AND curly arrow from lone pair to C of C—Br M2 correct dipole on C—Br AND curly arrow from bond to Br 2 4(c)(i) reducing agent / reductant 1 4(c)(ii) C2H2O3 + 2[H] → C2H4O3 M1 for correct molecular formulae C2H2O3 and C2H4O3 M2 for balancing 2 Question Answer Marks 4(d)(i) EITHER Glycolic acid would have: M1 2500–3000 due to − 2 RCO H M2 range within 3200–3650 due to RO–H OR Spectrum Y would NOT have: M1 2500–3000 due to − 2 RCO H M2 range within 3200–3650 due to RO–H 2 4(d)(ii) M1 ANY ester group AND valid C4H4O4 molecule M2 correct cyclic structure 2 O O O O

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