Cambridge A Level Chemistry 9701 — 2021 May/June Paper 2 · Variant 1

1 Ethanedioic acid, HO2CCO2H, has a relative molecular mass of 90.0. (a) (i) Explain what is meant by the term relative molecular mass. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) State the empirical formula of ethanedioic acid. ....................................................................................................................................... [1] (iii) Calculate how many atoms of carbon are present in 0.18 g of ethanedioic acid, HO2CCO2H. Show your working. atoms of carbon present = .............................. [3] (b) Solid ethanedioic acid reacts with aqueous calcium ions to make a precipitate of calcium ethanedioate, CaC2O4. CaC2O4 breaks down when heated to form calcium oxide, carbon dioxide and carbon monoxide. (i) Construct an equation to represent the reaction of CaC2O4 when heated. Include state symbols. ....................................................................................................................................... [2] (ii) Identify the type of reaction which occurs when CaC2O4 is heated. ....................................................................................................................................... [1] (iii) Identify another compound containing calcium ions which will also produce carbon dioxide and calcium oxide when it is heated. ....................................................................................................................................... [1] [Total: 10]

Mark scheme: 1(a)(i) option 1 M1 the mass of a molecule OR the (weighted) average / (weighted) mean mass of the molecule(s) 1 option 1 and M2 relative / compared to 1 / 12 (the mass) of an atom of carbon–12 1 OR on a scale in which a carbon–12 atom / isotope has a mass of (exactly) 12 (units) option 2 M1 mass of one mol of molecules option 2 M2 relative / compared to 1 / 12 (the mass) of 1 mol of C-12 OR which one mol C-12 (atom / isotope) has a mass of (exactly) 12 g 1(a)(ii) CO2H 1 1(a)(iii) 0.18/90 × 2 × 6.02 × 1023 = 2.408 × 1021 (atoms) OR 2.4(1) × 1021 (atoms) M1 no mole ethanedioic acid 0.18 / 90 = 0.0020 1 M2 no mole ethanedioic acid × 2 0.0020 × 2 = 0.0040 1 M3 no mole ethanedioic acid × 6.02 × 1023 2.4 × 1021 1 1(b)(i) CaC2O4(s)  CaO(s) + CO2(g) + CO(g) M1 correct formulae 1 M2 balancing equation AND state symbols. 1 1(b)(ii) (thermal) decomposition OR disproportionation 1 1(b)(iii) calcium carbonate / CaCO3 1

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2 Carbon monoxide gas, CO(g), and nitrogen gas, N2(g), are both diatomic molecules. (a) The diagram shows the arrangement of outer electrons in a molecule of CO(g). C O (i) State one similarity and one difference in the way the atoms in a carbon monoxide molecule are bonded together compared to the atoms in a nitrogen molecule. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) The table states the electronegativity values of carbon, nitrogen and oxygen atoms. C N O electronegativity 2.5 3.0 3.5 Use the electronegativity values and relevant details from the Data Booklet to complete the table below. N2 CO number of electrons per molecule type(s) of intermolecular (van der Waals’) force [2] (b) N2(g) is less reactive than CO(g) even though N2(g) has a lower bond energy than CO(g). Suggest why CO(g) is more reactive than N2(g). .................................................................................................................................................... .............................................................................................................................................. [1] (c) Both carbon monoxide and nitrogen are gases at room temperature and pressure. They both behave like ideal gases under certain conditions. (i) State the two conditions necessary for these two gases to approach ideal gas behaviour. ............................................................................................................................................. ....................................................................................................................................... [1] (ii) Explain why N2(g) behaves more like an ideal gas than CO(g) does at 20.0 °C and 101 kPa. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (d) Calculate the amount, in mol, of pure nitrogen gas which occupies 100 cm3 at 101 kPa and 20.0 °C. Use relevant information from the Data Booklet. Show your working. Assume nitrogen behaves as an ideal gas. .............................. mol [3] [Total: 11]

Mark scheme: 2(a)(i) M1 both make triple (covalent) bond / 3 shared pairs of electrons 1 M2 one bond in CO is coordinate / dative covalent / formed by donating a pair of electrons from O (to C) 1 2(a)(ii) N2 CO number of electrons per molecule 14 14 type of van der Waals’ temporary / instantaneous dipole–induced dipole permanent dipoles– (permanent) dipoles (and temporary / induced / instantaneous dipoles) 2 2(b) CO / it is a polar molecule / it has a (permanent) dipole (but N2 is non-polar) 1 2(c)(i) high temperature AND low pressure 1 2(c)(ii) M1 CO is polar / has a permanent dipole OR N2 is non-polar 1 M2 IMF in CO are (more) significant / larger OR IMF in N2 are smaller / less significant 1 Alternative answer M1 (Size of) N2 smaller than CO OR volume of N2 molecules / particles smaller Alternative answer M2 volume of N2 molecules / particles is more negligible ORA Question Answer Marks 2(d) M1 correct conversion to consistent units P = 101 000 V = 100 / 1 000 000 = (1 × 10–4) T = 293 1 M2 use of all values from M1 in correct relationship, n = PV / RT 1 M3 calculation = 4.15 × 10–3 mol 1

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3 Sodium halide salts react with concentrated sulfuric acid at room temperature. (a) (i) Write an equation to represent the reaction of NaCl (s) with concentrated sulfuric acid. ....................................................................................................................................... [1] (ii) Name this type of reaction. ....................................................................................................................................... [1] (b) NaI(s) reacts with concentrated sulfuric acid, at room temperature, to form steamy fumes. (i) Identify the chemical responsible for the steamy fumes. ....................................................................................................................................... [1] (ii) The reaction of NaI(s) with concentrated sulfuric acid continues, forming several other products, including a dark grey solid. Identify the chemical responsible for the dark grey solid and one other product of this further reaction. dark grey solid ..................................................................................................................... other product ....................................................................................................................... [2] (c) Explain the differences in observations, at room temperature, when NaI(s) reacts with concentrated sulfuric acid compared to those for NaCl (s). .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (d) Complete the equation for the reaction of Br – with excess concentrated H2SO4 at room temperature. ......Br – + ......H+ + ......H2SO4 → ............................................................................... [1] [Total: 8]

Mark scheme: 3(a)(i) OR 2NaCl + H2SO4  Na2SO4 + 2HCl 1 3(a)(ii) displacement / acid-base (reaction) 1 3(b)(i) hydrogen iodide / HI 1 3(b)(ii) dark grey solid I2 / iodine 1 other product S / sulfur OR H2S / hydrogen sulfide OR H2O / water / steam 1 3(c) M1 iodide ions are strong(er) reducing agents (than chloride ions) ORA 1 M2 HI / iodide is oxidised OR HCl / chloride is not oxidised 1 3(d) 2Br– + 2H+ + H2SO4  Br2 + 2H2O + SO2 1

More questions on The chemical properties of the halogen elements and the hydrogen halides

4 Aqueous bromine reacts with methanoic acid to form hydrogen bromide and carbon dioxide gas. Br2(aq) + HCO2H(aq) → 2HBr(aq) + CO2(g) The table shows the oxidation numbers of bromine and carbon in the species involved in this reaction. Br in Br2 C in HCO2H Br in HBr C in CO2 oxidation number 0 +2 –1 +4 (a) Identify the oxidising agent in this reaction. Explain your reasoning with reference to oxidation numbers. .................................................................................................................................................... .............................................................................................................................................. [1] (b) Suggest one change you would observe, ignoring temperature changes, when bromine reacts with methanoic acid. .............................................................................................................................................. [1] (c) This reaction can be followed by measuring the concentration of bromine present in the mixture at regular time intervals. The graph shows the change in concentration of bromine against time in a reaction carried out at 20 °C. 100 80 60 [Br2] 105 / mol dm–3 40 20 0 0 100 200 300 400 500 600 time / s (i) Use the graph to calculate the average rate of reaction at 20 °C during the first 600 s. State the units of this rate of reaction. average rate of reaction .............................................. units .............................................. [2] The experiment is repeated at a temperature of 40 °C. This relatively small increase in temperature produces a large increase in reaction rate. (ii) Sketch a graph, on the same axes, to show the expected results when repeating the experiment at 40 °C. [1] (iii) The rate of reaction increases when the frequency of successful collisions between reactant particles increases. Explain why an increase in temperature produces this effect. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (d) Complete the ‘dot-and-cross’ diagram, showing outer electrons only, to show the bonding in methanoic acid, HCO2H. O C H O H [2] [Total: 9]

Mark scheme: 4(a) Br / bromine as the oxidation number of Br decreases / goes from 0 → –1 OR bromine as it causes oxidation number of C (in methanoic acid) to increase / go from (+)2 → (+)4 1 4(b) (solution) turns (from brown / orange / red to) colourless / decolorises OR brown / orange / red fades 1 4(c)(i) rate = total change in concentration of Br2 divided by time taken calculation dependent on graph (100 × 10–5 – 12 × 10–5) / 600 M1 average rate of reaction 1.47 × 10–6 1 M2 units mol dm–3 s–1 1 4(c)(ii) graph shown on same axes has steeper initial gradient AND reaches the same final [Br2] 1 4(c)(iii) M1 (at increased temp the average kinetic) energy of particles / species / molecules increases. 1 M2 (many) more/greater proportion of particles with energy ⩾ Ea 1 4(d) M1 correct bonding electrons 1 M2 correct number of non-bonding electrons around each oxygen 1

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5 (a) Naphtha is a mixture which contains only hydrocarbon molecules. (i) What is meant by the term hydrocarbon? ............................................................................................................................................. ....................................................................................................................................... [1] (ii) Name the raw material that is used to produce a sample of naphtha. ....................................................................................................................................... [1] (b) Compound V is found in naphtha. It has a molecular formula C10H22. When V is heated at high pressure in the absence of air, an equal number of moles of ethene, propene and W are made. W is a compound made of straight chain, saturated molecules. (i) Name the process that describes this reaction. ....................................................................................................................................... [1] (ii) Deduce the structure of W. Draw its structure below. [1] (c) Propene is separated from the mixture and heated in air in the presence of a catalyst. Propene is oxidised to X, which contains two functional groups. (i) Effervescence is seen when Na2CO3(aq) is added to X. Identify the functional group present in X which is responsible for this observation. ....................................................................................................................................... [1] (ii) Identify a reagent which could be used to show that X contains a C=C. Include relevant observations. ............................................................................................................................................. ....................................................................................................................................... [2] (d) X reacts with another reagent to form Y. Molecules of Y react together to form addition polymer Z. The diagram shows the repeat unit of polymer Z. repeat unit of polymer Z O O– Na+ Draw the structural formula of monomer Y. [1] (e) Polymer Z is useful because it absorbs large amounts of water. However, there are problems associated with the disposal of products containing polymer Z. Combustion is not an appropriate method to dispose of pure Z because the process releases harmful gases. Some of these gases contribute to the enhanced greenhouse effect. (i) Identify a gas released during the combustion of Z which contributes to the enhanced greenhouse effect. ....................................................................................................................................... [1] (ii) Identify another gas which could be produced during the combustion of pure Z. Describe a consequence, other than the enhanced greenhouse effect, of its release into the atmosphere. gas ...................................................................................................................................... consequence ....................................................................................................................... [1] [Total: 10]

Mark scheme: 5(a)(i) (compounds / molecules) containing only / entirely carbon and hydrogen (atoms) 1 5(a)(ii) crude oil 1 5(b)(i) (thermal) cracking 1 5(b)(ii) structure of W OR CH3(CH2)3CH3 OR 1 5(c)(i) CO2H / carboxylic acid 1 5(c)(ii) M1 (add) Br2(aq) / bromine water 1 M2 (solution) turns (from brown / orange / red to) colourless / decolorises OR brown / orange / red fades 1 5(d) OR CH2CH(CO2(–)Na(+)) OR CH2=CH(COO(–)Na(+)) OR OR , etc. 1 5(e)(i) carbon dioxide / CO2 1 5(e)(ii) CO / hydrocarbons AND toxic / poisonous / harmful to health / (catalyses formation of) photochemical smog 1

More questions on Alkanes

6 Propene, C3H6, reacts with H2O in the presence of an acid catalyst to form an alcohol with molecular formula C3H8O. (a) Name this type of reaction. .............................................................................................................................................. [1] (b) Name the catalyst used and state the conditions needed for this reaction to occur. catalyst ....................................................................................................................................... conditions ................................................................................................................................... [2] (c) Complete the table to show the numbers of sigma (σ) bonds and pi (π) bonds present in propene, C3H6, and C3H8O. σ π C3H6 C3H8O [2] (d) The reaction of propene, C3H6, with H2O occurs in a two-step mechanism. In step 1 C3H6 reacts with the catalyst, H+, to form a carbocation. (i) Draw structures to identify the more stable and less stable carbocations which can form in step 1. Explain your answer. more stable carbocation less stable carbocation explanation .......................................................................................................................... ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. [3] (ii) Name the major organic product formed from the reaction of propene, C3H6, with H2O. ....................................................................................................................................... [1] (e) 2-bromopropane reacts to form propene, hydrogen bromide and water under certain conditions. (i) Name this type of reaction. ....................................................................................................................................... [1] (ii) Describe the reagents and conditions needed to favour this reaction. reagents .............................................................................................................................. conditions ............................................................................................................................ [2] [Total: 12]

Mark scheme: 6(a) addition 1 6(b) M1 catalyst = sulfuric acid / phosphoric(V) acid 1 M2 conditions of reaction = steam / heat (and pressure) 1 6(c) σ π C3H6 8 1 C3H8O 11 0 2 6(d)(i) M1 more stable = CH3C+(H)(CH3) 1 M2 less stable = CH3CH2C+(H2) / 1 M3 greater (positive) inductive effect of two alkyl groups OR greater electron donation of two alkyl groups owtte 1 6(d)(ii) propan-2-ol 1 6(e)(i) elimination 1 6(e)(ii) M1 NaOH / KOH 1 M2 ethanolic solution / ethanol / alcohol + heat 1

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