OCR AS Level Chemistry A H032/02 Depth in Chemistry 2019 QUESTIONS

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PMT Oxford Cambridge and RSA AS Level Chemistry A H032/02 Depth in Chemistry Friday 25 May 2019 – Morning Time allowed: 1 hour 30 minutes * H 0 3 2 0 2 * INSTRUCTIONS • Use black ink. HB p... encil may be used for graphs and diagrams. • Complete the boxes above with your name, centre number and candidate number. • Answer all the questions. • Write your answer to each question in the space provided. If additional answer space is required, you should use the lined page(s) at the end of the booklet. The question number(s) must be clearly shown. • Do not write in the barcodes. INFORMATION • The total mark for this paper is 70. • The marks for each question are shown in brackets [ ]. • Quality of extended responses will be assessed in questions marked with an asterisk (*). • This document consists of 20 pages. © OCR 2018 [601/5256/4] DC (LK/SG) 152268/5 OCR is an exempt Charity Turn over You must have: the Data Sheet for Chemistry A (sent with general stationery) You may use: a scientific or graphical calculator * 7 0 0 4 2 5 7 6 2 3 * First name Last name Centre CandidatePMT 2 © OCR 2018 Answer all the questions. 1 A student carries out a titration to determine the molar mass and structure of a weak acid A. The student follows the method below. • Dissolve a weighed mass of A in 100cm3 of distilled water and make the solution up to 250 cm3 in a beaker. • Add the solution of A to a burette. • Titrate the solution of A with a standard solution of sodium hydroxide, NaOH. (a) What is meant by the term standard solution? ................................................................................................................................................... .............................................................................................................................................. [1] (b) Sodium hydroxide is an alkali. What is meant by the term alkali? ................................................................................................................................................... .............................................................................................................................................. [1] (c) The student carries out a trial, followed by three further titrations. The diagram shows the initial and final burette readings for the three further titrations. The student measures all burette readings to the nearest 0.05cm3 . Titration 1 Titration 2 Titration 3 Initial reading Final reading Initial reading Final reading Initial reading Final reading 0 27 0 27 0 27 1 28 1 28 1 28 2 29 2 29 2 29© OCR 2018 Turn over PMT 3 (i) Record the student’s readings and the titres in the table below. Calculate the mean titre, to the nearest 0.05 cm3 , that the student should use for analysing the results. Titration 1 Titration 2 Titration 3 Final reading/cm3 Initial reading/cm3 Titre/cm3 mean titre = ................................................... cm3 [4] (ii) The uncertainty in each burette reading is ± 0.05 cm3 . Calculate the percentage uncertainty for the titre in Titration 1. percentage uncertainty = ...................................................... % [1] (iii) The student realised that the solution of A had not been prepared correctly. How should the student have made up the solution? ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]© OCR 2018 PMT 4 (d) A student repeats the titration to determine the molar mass and structure of A. • The student prepares a 250.0 cm3 solution from 1.513 g of A. • The solution of A is added to the burette and titrated with 25.0cm3 volumes of 0.112 moldm–3 NaOH(aq). • 1 mol of A reacts with 2 mol of NaOH. • The student obtains a mean titre of 27.30 cm3 . (i) Calculate the molar mass of A from these results. Give your answer to the nearest whole number. Show your working. molar mass of A = .............................................. g mol–1 [4] (ii) A is an organic acid, containing C, H and O only. One molecule of A contains two COOH groups. Suggest the structure of A. [1]© OCR 2018 Turn over PMT 5 2 Sodium sulfide, Na2S, is an ionic compound of sodium, Na, and sulfur, S. (a) Draw a ‘dot-and-cross’ diagram to show the bonding in sodium sulfide. Show outer electrons only. [2] (b) The table below compares the properties of sodium sulfide, sodium and sulfur. Complete the table. Sodium sulfide Sodium Sulfur Melting point / °C 1180 98 113 Type of structure (giant or simple) Electrical conductivity (good or poor) solid liquid [3] (c) Selenium is in the same group of the periodic table as sulfur. (i) Complete the full electron configuration of a selenium atom. 1s2...............................................................................................................................[1] (ii) Sodium selenide reacts with hydrochloric acid to form a toxic gas, B, with a relative molecular mass of 81.0. Identify gas B and write an equation for this reaction. Gas B ..................... Equation...................................................................................................................... [2]© OCR 2018 PMT 6 3 This question is about halogens. (a) Bromine is used to extract iodine from a solution containing iodide ions. (i) Write an ionic equation for the reaction. ...................................................................................................................................... [1] (ii) Explain why iodine is less reactive than bromine. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3] (b) Iodine can be used for the small-scale purification of drinking water. (i) Iodine reacts with water as shown below. I2 + H2O HI + HIO Using oxidation numbers, explain why this reaction is a disproportionation. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3] (ii) Chlorine is used to purify water on a large scale. State one disadvantage of using chlorine for the purification of drinking water. ........................................................................................................................................... ...................................................................................................................................... [1]© OCR 2018 Turn over PMT 7 (c) Hydrogen reacts with chlorine to form hydrogen chloride, HCl: H2 (g) + Cl 2 (g) 2HCl(g) ∆H = –184 kJ mol–1 Table 3.1 shows bond enthalpies. Bond Bond Enthalpy/kJ mol–1 H–H +436 Cl–Cl +243 Table 3.1 Calculate the bond enthalpy for the H–Cl bond from the information above. bond enthalpy = .............................................kJ mol–1 [2] (d) ‘Enthalpy change of vaporisation’ is the enthalpy change when one mole of a substance changes from a liquid to a gas at its boiling point. (i) Write an equation, including state symbols, to represent the enthalpy change of vaporisation of bromine. ...................................................................................................................................... [1] (ii) Suggest whether the enthalpy change of vaporisation of bromine is exothermic or endothermic. Explain your answer. ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]PMT © OCR 2018 8 4 The reaction of ammonia, NH3 , with oxygen to form nitrogen monoxide, NO, is an important industrial process. The equation for this reaction is shown in equilibrium 4.1 below. 4NH3 (g) + 5O2 (g) 4NO(g) + 6H2O(g) ∆H = –905 kJ mol–1 Equilibrium 4.1 (a) The forward reaction in equilibrium 4.1 converts NH3 into NO. (i) Complete the enthalpy profile diagram for this reaction. On your diagram: • Label the activation energy, Ea • Label the enthalpy change of reaction, ∆H • Include the formulae of the reactants and products. Enthalpy Progress of reaction [2] (ii) 5.10 tonnes of NH3 are converted into NO. Calculate the energy released, in kJ, for this conversion. Give your answer in standard form and to an appropriate number of significant figures. energy released = ......................................................kJ [4]PMT 9 © OCR 2018 Turn over (b) Write an expression for the equilibrium constant, Kc , in equilibrium 4.1. [1] (c) Predict the conditions of temperature and pressure for a maximum equilibrium yield of nitrogen monoxide in equilibrium 4.1. • Explain your prediction in terms of le Chatelier’s principle. • State and explain how these conditions could be changed to achieve a compromise between equilibrium yield, rate and other operational factors. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5]PMT 10 © OCR 2018 5 (a) 1-Bromobutane is an organic liquid with a boiling point of 102 °C. A student prepares 1-bromobutane by reacting butan-1-ol with sulfuric acid and sodium bromide. The student boils the mixture for one hour. The equation is shown below. CH3CH2CH2CH2OH + H + + Br – CH3CH2CH2CH2Br + H2O The student obtains a reaction mixture containing an organic layer (density = 1.27g cm–3 ) and an aqueous layer (density = 1.00g cm–3 ). (i)* Draw a labelled diagram to show how you would safely set up apparatus for thepreparation. Outline a method to obtain a pure sample of 1-bromobutane from the reaction mixture. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [6]PMT © OCR 2018 Turn over 11 (ii) The student used 0.150mol of butan-1-ol. The student obtained a 61.4% percentage yield of 1-bromobutane. Calculate the mass of 1-bromobutane obtained. Give your answer to three significant figures. mass = ....................................................... g [2]PMT 12 © OCR 2018 (b) A student investigates the rate of reaction of 1-bromobutane with aqueous hydroxide ions. The graph shows how the hydroxide ion concentration, [OH– (aq)], changes during the reaction. [OH– (aq)] / mol dm–3 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0 50 100 time / min 150 200 Using the graph, calculate the rate of reaction, in moldm–3min–1 , at 30 minutes. Show your working on the graph and in the space below. rate of reaction = .................................. mol dm–3 min–1 [2]PMT © OCR 2018 Turn over 13 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGEPMT © OCR 2018 14 6 Two reactions of compound C are shown in the flowchart below. H Cl C C H Cl Compound C Reaction 1 Reaction 2 H Cl H Cl H C C OH H C C Cl H Cl Br Br Compound D (a) State the reagents and conditions for reaction 1. ................................................................................................................................................... .............................................................................................................................................. [1] (b) In reaction 2, compound C reacts with bromine to form compound D. (i) Give the systematic name of compound D. ...................................................................................................................................... [1] (ii) Outline the mechanism for reaction 2. Include curly arrows, charges and relevant dipoles. [3]PMT 15 © OCR 2018 Turn over (c) Compound C forms an addition polymer E. (i) Write a balanced equation for this reaction. Show displayed formulae. [2] (ii) State one advantage and one disadvantage of using combustion as a method for the disposal of waste polymer E. Advantage ......................................................................................................................... ........................................................................................................................................... Disadvantage .................................................................................................................... ...................................................................................................................................... [2]PMT © OCR 2018 16 7* Compound F is a trans stereoisomer which is a useful intermediate in organic synthesis. The results of elemental and spectral analysis of compound F are shown below. Percentage composition by mass: C, 68.6 %; H, 8.6 %; O, 22.8 %. Infrared spectrum 100 transmittance (%) 50 0 4000 3000 2000 1500 1000 500 wavenumber / cm–1 Mass spectrum 100 80 60 relative intensity 40 20 0 10 20 30 40 50 m/z 60 70 80PMT 17 © OCR 2018 In the mass spectrum, the peak with the greatest relative intensity is caused by the loss of a functional group from the molecular ion of compound F. Determine the structure of compound F. Explain your reasoning and show your working. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [6] END OF QUESTION PAPERPMT 18 © OCR 2018 ADDITIONAL ANSWER SPACE If additional space is required, you should use the following lined page(s). 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