Cambridge A Level Chemistry 9701 — 2011 May/June Paper 2 · Variant 2

This document consists of 11 printed pages and 1 blank page. DC (NF/DJ) 27049/4 © UCLES 2011 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level * 9 9 9 2 0 0 6 7 0 1 * CHEMISTRY 9701/22 Paper 2 Structured Questions AS Core May/June 2011 1 hour 15 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, Centre number and candidate number on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs, or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE ON ANY BARCODES. Answer all questions. You may lose marks if you do not show your working or if you do not use appropriate units. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. For Examiner’s Use 1 2 3 4 5 Total

2 9701/22/M/J/11 © UCLES 2011 For Examiner’s Use Answer all the questions in the spaces provided. 1 Ethanoic acid can be reacted with alcohols to form esters, an equilibrium mixture being formed. CH3CO2H + ROH CH3CO2R + H2O The reaction is usually carried out in the presence of an acid catalyst. (a) Write an expression for the equilibrium constant, Kc, for this reaction, clearly stating the units. Kc = units … [2] In an experiment to determine Kc a student placed together in a conical flask 0.10 mol of ethanoic acid, 0.10 mol of an alcohol ROH, and 0.005 mol of hydrogen chloride catalyst. The flask was sealed and kept at 25 °C for seven days. After this time, the student titrated all of the contents of the flask with 2.00 mol dm–3 NaOH using phenolphthalein indicator. At the end-point, 22.5 cm3 of NaOH had been used. (b) (i) Calculate the amount, in moles, of NaOH used in the titration. (ii) What amount, in moles, of this NaOH reacted with the hydrogen chloride? (iii) Write a balanced equation for the reaction between ethanoic acid and NaOH. (iv) Hence calculate the amount, in moles, of NaOH that reacted with the ethanoic acid. [4]

3 9701/22/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use (c) (i) Use your results from (b) to calculate the amount, in moles, of ethanoic acid present at equilibrium. Hence complete the table below. CH3CO2H ROH CH3CO2R H2O initial amount / mol 0.10 0.10 0 0 equilibrium amount / mol (ii) Use your results to calculate a value for Kc for this reaction. [3] (d) Esters are hydrolysed by sodium hydroxide. During the titration, sodium hydroxide reacts with ethanoic acid and the hydrogen chloride, but not with the ester. Suggest a reason for this. … … [1] (e) What would be the effect, if any, on the amount of ester present if all of the water were removed from the flask and the flask kept for a further week at 25 °C? Explain your answer. … … … [2] [Total: 12]

4 9701/22/M/J/11 © UCLES 2011 For Examiner’s Use 2 Halogenoalkanes have been widely used as aerosol propellants, refrigerants and solvents for many years. Fluoroethane, CH3CH2F, has been used as a refrigerant. It may be made by reacting ethene with hydrogen fluoride. You are to calculate a value for the C–F bond energy in fluoroethane. (a) Use relevant bond energies from the Data Booklet, and the equation below to calculate a value for the bond energy of the C–F bond. CH2 = CH2(g) + HF(g) CH3CH2F(g) ΔH o = – 73 kJ mol–1 C–F bond energy = … kJ mol–1 [4] (b) Another halogenoalkane which was used as a refrigerant, and also as an aerosol propellant, is dichlorodifluoromethane, CCl2F2. State two reasons why compounds such as CH3CH2F and CCl2F2 have been used as aerosol propellants and refrigerants. … … [2]

5 9701/22/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use CCl2F2 is one of many chlorofluorocarbon compounds responsible for damage to the ozone layer in the stratosphere. (c) By using relevant data from the Data Booklet, and your answer to (a) suggest why CCl2F2 is responsible for damage to the ozone layer in the stratosphere whereas CH3CH2F is not. … … … [2] Both CH3CH2F and CCl2F2 are greenhouse gases. The ‘enhanced greenhouse effect’ is of great concern to the international community. (d) (i) What is meant by the term enhanced greenhouse effect? … … … (ii) Water vapour is the most abundant greenhouse gas. What is the second most abundant greenhouse gas? … [3] A greenhouse gas which is present in very small amounts in the atmosphere is sulfur hexafluoride, SF6, which is used in high voltage electrical switchgear. (e) What shape is the SF6 molecule? … [1] [Total: 12]

6 9701/22/M/J/11 © UCLES 2011 For Examiner’s Use 3 Barium, proton number 56, is a Group II element which occurs in nature as the carbonate or sulfate. The element was first isolated by Sir Humphry Davy in 1808. Some reactions of barium and its compounds are shown in the reaction scheme below. Ba(s) R(s) heat gently in oxygen H2O(l) U(s) S(aq) T(aq) dilute HCl dilute H2SO4 dilute HNO3 reaction 1 W(aq) Na2CO3(aq) V(s) (a) State the formula of each of the barium compounds R to W. R … S … T… U … V … W … [6] (b) (i) Write balanced equations for the following reactions. compound T to compound W … the roasting of V in air …

7 9701/22/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use (ii) Suggest a gaseous reagent for the conversion of T into V and write a balanced equation for the reaction. reagent … equation … [4] (c) Suggest the formula of an aqueous reagent, other than an acid, for reaction 1. ………………………… [1] When barium is heated strongly in oxygen, an oxide X is formed. The oxide X contains 18.9% of oxygen by mass. The oxide X reacts with dilute sulfuric acid in a 1:1 ratio. Two products, one insoluble and one soluble, are formed. Ba(s) X(s) heat strongly in oxygen Y(s) + dilute H2SO4 Z(aq) + (d) (i) Calculate the empirical formula of X. (ii) Suggest the identity of the solid Y. … (iii) Use your answers to (i) and (ii) to construct an equation for the reaction of X with H2SO4. … [4] [Total: 15]

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9 9701/22/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use 4 Chlorine is manufactured by electrolysis from brine, concentrated aqueous sodium chloride. (a) (i) Describe, with the aid of a fully labelled diagram, the industrial electrolysis of brine in a diaphragm cell. State what each electrode is made of and show clearly the inlet for the brine and the outlets for the products. (ii) Write a half-equation, with state symbols, for the reaction at each electrode. anode … cathode … (iii) Name the chemical that is produced in solution in this electrolytic process. … [7] [Total: 7]

10 9701/22/M/J/11 © UCLES 2011 For Examiner’s Use 5 Although there are many different types of food eaten around the world, animal fats and/or vegetable oils are commonly used in cooking. Animal fats and vegetable oils are usually glyceryl esters, that is esters of glycerol, propane-1,2,3-triol. CH2OH ⏐ CHOH ⏐ CH2OH Many animal fats contain esters of stearic acid, CH3(CH2)16CO2H. Vegetable oils often contain esters of oleic acid, CH3(CH2)7CHCH(CH2)7CO2H. (a) Draw the structural formula of the glyceryl ester formed when one molecule of glycerol is completely esterified with stearic acid. [1] (b) What reagent(s) would you use, in a school or college laboratory, to obtain a small sample of oleic acid, C17H33CO2H, from the glyceryl ester present in a vegetable oil? … [1] Oleic acid is the cis isomer and elaidic acid the trans isomer of CH3(CH2)7CHCH(CH2)7CO2H. (c) By using this formula, draw the structural formula of elaidic acid, clearly showing the stereochemistry. [1]

11 9701/22/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use Oleic and elaidic acids are examples of mono-unsaturated acids. Many vegetable oils contain esters of polyunsaturated fatty acids. Such oils are often hydrogenated to form esters containing saturated or mono-unsaturated fatty acids. (d) (i) Suggest the meaning of the term polyunsaturated fatty acid. … … (ii) What reagent and condition(s) are used for the hydrogenation of an unsaturated fatty acid? reagent … condition(s) … [3] In cooking, unsaturated fats are often oxidised to give aldehydes or ketones. (e) (i) Give the structural formulae of the two aldehydes formed by the partial oxidation of the unsaturated fat below. In the structure, X, represents the rest of the fat molecule. CH3(CH2)7CHCH(CH2)7X (ii) Name the reagent you would use to show that the product contained either an aldehyde or a ketone. What change would be seen? reagent … observation … (iii) What reagent would you use to confirm the presence of an aldehyde? What change would be seen? reagent … observation … [6]

12 9701/22/M/J/11 © UCLES 2011 For Examiner’s Use Animal fats and vegetable oils can become rancid because of oxidation. The rancid fat or oil has an unpleasant smell and taste. Antioxidants are used to prevent the spoilage of many foodstuffs by oxidation. One antioxidant that is widely used is vitamin C, ascorbic acid. HO HO H O O ascorbic acid OH HO (f) (i) How many chiral carbon atoms are present in one molecule of ascorbic acid? If none, write ‘none’. … (ii) The ascorbic acid molecule contains three functional groups. Two of these are alcohol (primary and secondary) and alkene. What is the name of the third functional group? … [2] [Total: 14] Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2011 question paper for the guidance of teachers 9701 CHEMISTRY 9701/22 Paper 2 (AS Structured Questions), maximum raw mark 60 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes must be read in conjunction with the question papers and the report on the examination. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the May/June 2011 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 22 © University of Cambridge International Examinations 2011 1 (a) Kc = [CH3CH2R][H20] [CH3CH2H][ROH] (1) no units (1) [2] (b) (i) n(NaOH) = 22.5 x 2.00 = 0.045 (1) 1000 (ii) n(NaOH) = n(HCl) = 0.005 (1) (iii) CH3CO2H + NaOH → CH3CO2Na + H2O (1) (iv) n(NaOH) = 0.045 – 0.005 = 0.04 allow ecf on (i) and/or (ii) (1) [4] (c) (i) n(NaOH) and n(CH3CO2H) = 0.04 (1) n(CH3CO2R) and n(H2O) = 0.06 (1) (ii) Kc = 0.06 x 0.06 = 2.25 0.04 x 0.04 allow ecf on wrong values in (b)(i) allow ecf on wrong expression in (a) (1) [3] (d) Ea for reaction with ester is high or Ea for reaction with acid is low or reaction with ester is slow or reaction with acid is fast (1) [1] (e) equilibrium moves to RHS/more ester would be formed (1) to maintain value of Kc or to restore system to equilibrium (1) [2] [Total: 12]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 22 © University of Cambridge International Examinations 2011 2 (a) CH2=CH2 + HF → CH3CH2F bonds 4 C-H 1640 bonds 5 C-H 2050 broken 1 C=C 610 made 1 C-C 350 /kJ mol-1 1 H-F 562 /kJ mol-1 1 C-F E 2812 (2400 + E) breaking reactant bonds requires 4 x 410 + 610 + 562 = 2812 kJ mol-1 (1) making product bonds gives 5 x 410 + 350 + E = (2400 + E) kJ mol-1 (1) ∆Ho reaction = - (2400 + E) + 2812 = – 73 kJ mol-1 (1) (2400 + E) = 2812 + 73 = 2885 kJ mol-1 E = 2885 - 2400 = 485 kJ mol-1 (1) allow ecf on wrong bond energy values and/or incorrect arithmetic [4] (b) any two from non-toxic unreactive volatile non-flammable easily liquefied (1 + 1) [2] (c) in CCl2F2 C-Cl bond energy is 340 kJ mol-1 and is weaker than C-F or C-H bonds (1) C-Cl bond is broken by uvl or Cl. free radicals are formed (1) [2] (d) (i) the trapping of reflected heat from the Earth in the lower atmosphere producing global warming (ii) CO2/carbon dioxide (1) [3] (e) octahedral (1) [1] [Total: 12]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 22 © University of Cambridge International Examinations 2011 3 heat gently in oxygen H2O(l) dilute HCl dilute H2SO4 Na2CO3(aq) dilute HNO3 reaction 1 (a) R BaO (1) S BaCl2 (1) T Ba(OH)2 (1) U BaSO4 (1) V BaCO3 (1) W Ba(NO3)2 (1) [6] (b) (i) T to W Ba(OH)2 + 2HNO3 → Ba(NO3)2 + 2H2O (1) heat on V BaCO3 → BaO + CO2 (1) (ii) T to V CO2 (1) Ba(OH)2 + CO2 → BaCO3 + H2O (1) [4] (c) Na2SO4(aq)/K2SO4(aq) or any soluble sulfate (1) [1] Ba(s) R(s) BaO Ba(s) W(aq) Ba(NO3)2 V(s) BaCO3 S(aq) BaCl2 T(aq) Ba(OH)2 U(s) BaSO4

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 22 © University of Cambridge International Examinations 2011 (d) (i) Ba:O = 81.1 : 18.9 (1) 137 16 = 0.59 : 1.18 = 1 : 2 gives BaO2 (1) (ii) BaSO4 (1) (iii) BaO2 + H2SO4 → BaSO4 + H2O2 (1) [4] [Total: 15] 4 (a) (i) titanium/graphite anode identified correctly (1) steel cathode identified correctly (1) diaphragm identified correctly (1) all three outlets correctly shown (1) [4] (ii) anode 2Cl–(aq) → Cl2(g) + 2e– (1) cathode 2H+(aq) + 2e– → H2(g) or 2H2O(l) + 2e– → H2(g) + 2OH–(aq) (1) [2] (iii) sodium hydroxide (1) [1] [Total: 7] brine H2(g) NaOH(aq) Cl2(g) steel cathode NaCl(aq) titanium/graphite anode + – diaphragm

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 22 © University of Cambridge International Examinations 2011 5 (a) CH2OCO(CH2)16CH3  CHOCO(CH2)16CH3  CH2OCO(CH2)16CH3 all three alcohol groups must be esterified (1) [1] (b) dilute HCl or dilute H2SO4 or dilute mineral acid or NaOH(aq) followed by dilute acid (1) [1] (c) C C H (CH2)7CO2H CH3(CH2)7 H (1) [1] (d) (i) fatty acid that contains more than one C=C bond (1) (ii) hydrogen (1) nickel/Raney nickel/platinum/palladium (1) [3] (e) (i) CH3(CH2)7CHO (1) OHC(CH2)7CX (1) (ii) 2,4-dinitrophenylhydrazine (1) yellow/orange/red precipitate (1) (iii) Tollens’ reagent or Fehling’s/Benedict's solution (1) silver mirror/ or brick red ppt. grey precipitate (1) [6] (f) (i) two (1) (ii) ester (1) [2] [Total: 14]