Cambridge A Level Chemistry 9701 — 2009 Oct/Nov Paper 2 · Variant 1

This document consists of 11 printed pages and 1 blank page. DC SJF4800/DT 15628/4 © UCLES 2009 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level 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. * 2 7 4 4 3 8 4 4 9 6 * CHEMISTRY 9701/21 Paper 2 Structured Questions AS Core October/November 2009 1 hour 15 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet For Examiner’s Use 1 2 3 4 5 Total

2 9701/21/O/N/09 © UCLES 2009 For Examiner’s Use Answer all the questions in the spaces provided. 1 Magnesium, Mg, and radium, Ra, are elements in Group II of the Periodic Table. Magnesium has three isotopes. (a) Explain the meaning of the term isotope. … … … [2] A sample of magnesium has the following isotopic composition by mass. isotope mass 24 25 26 % by mass 78.60 10.11 11.29 (b) Calculate the relative atomic mass, Ar, of magnesium to four significant figures. Ar = ……………… [2]

3 9701/21/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use Radium, proton number 88, and uranium, proton number 92, are radioactive elements. The isotope 226Ra is produced by the radioactive decay of the uranium isotope 238U. (c) Complete the table below to show the atomic structures of the isotopes 226Ra and 238U. number of isotopes protons neutrons electrons 226Ra 238U [3] (d) Radium, like other Group II elements, forms a number of ionic compounds. (i) What is the formula of the radium cation? ……………… (ii) Use the Data Booklet to suggest a value for the energy required to form one mole of the gaseous radium cation you have given in (i) from one mole of gaseous radium atoms. Explain your answer. … … … [3] [Total: 10]

4 9701/21/O/N/09 © UCLES 2009 For Examiner’s Use 2 Radium was discovered in the ore pitchblende by Marie and Pierre Curie in 1898, and the metal was first isolated by them in 1910. The metal was obtained by first reacting the radium present in the pitchblende to form insoluble radium sulfate which was converted into aqueous radium bromide. This solution was then electrolysed using a mercury cathode and a carbon anode. (a) Radium has chemical reactions that are typical of Group II metals and forms ionic compounds. (i) What is the characteristic feature of the electronic configurations of all Group II metals? … (ii) Radium sulfate is extremely insoluble. From your knowledge of the simple salts of Group II metals, suggest another very insoluble radium salt. … [2] (b) During their electrolysis of aqueous radium bromide, the Curies obtained radium at the cathode and bromine at the anode. Write half-equations for the two electrode reactions that take place during this electrolysis. anode … cathode … [2] (c) (i) Describe what you would see when magnesium reacts with cold water, … … steam. … … (ii) Write an equation for the reaction with steam. … [5]

5 9701/21/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (d) Radium reacts vigorously when added to water. (i) Write an equation, with state symbols, for this reaction. … (ii) State two observations that could be made during this reaction. … … (iii) Suggest the approximate pH of the resulting solution. ……………… (iv) Will the reaction be more or less vigorous than the reaction of barium with water? Explain your answer. … … [6] [Total: 15]

6 9701/21/O/N/09 © UCLES 2009 For Examiner’s Use 3 Alkanes such as methane, CH4, undergo few chemical reactions. Methane will, however, react with chlorine but not with iodine. Relevant standard enthalpy changes of formation for the reaction of methane with chlorine to form chloromethane, CH3Cl, are given below. ∆H f o /kJ mol–1 CH4 –75 CH3Cl –82 HCl –92 (a) (i) Use the data to calculate ∆H reaction for the formation of CH3Cl. CH4 + Cl 2 → CH3Cl + HCl (ii) The corresponding reaction with iodine does not take place. Use bond energy data from the Data Booklet to calculate a ‘theoretical value’ for ∆Hreaction for the following equation. CH4 + I2 → CH3I + HI (iii) Suggest why this reaction does not in fact occur. … … [5]

7 9701/21/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (b) (i) By using equations, describe the mechanism of the reaction between chlorine and methane to form chloromethane, CH3Cl. Identify, by name, the separate steps of the overall reaction. … … … … … … (ii) What is the intermediate organic species in this reaction? … [7] (c) The energy of activation for the formation of CH3Cl is 16 kJ mol–1. Use this figure and your answer to (a)(i) to complete the reaction pathway diagram below showing the formation of CH3Cl from CH4 and Cl2. Show clearly the intermediate organic species and the final products. Indicate on your sketch the relevant enthalpy changes and their values. enthalpy progress of reaction CH4 + Cl2 [4] [Total: 16]

8 9701/21/O/N/09 © UCLES 2009 For Examiner’s Use 4 The structural formulae of six different compounds, A – F, are given below. Each compound contains four carbon atoms in its molecule. CH3CH=CHCH3 CH3CH2COCH3 CH2=CHCH2CH3 A B C CH3CH2CH(OH)CH3 HOCH2CH2CH2CH2OH CH3CH2OCH2CH3 D E F (a) (i) What is the empirical formula of compound E? ……………… (ii) Draw the skeletal formula of compound D. (iii) Structural formulae do not show all of the isomers that may exist for a given molecular formula. Which two compounds each show different types of isomerism and what type of isomerism does each compound show? Identify each compound by its letter. compound type of isomerism [4] Compound D may be converted into compound C. (b) (i) What type of reaction is this? ……………………………………… (ii) What reagent would you use for this reaction? ……………………………………… (iii) What is formed when compound E undergoes the same reaction using an excess of the same reagent? ……………………………………… [3]

9 9701/21/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use Compound A may be converted into compound B in a two-stage reaction. CH3CH=CHCH3 → stage I intermediate → stage II CH3CH2COCH3 (c) (i) What is the structural formula of the intermediate compound formed in this sequence? (ii) Outline how stage I may be carried out to give this intermediate compound. … … … (iii) What reagent would be used for stage II? ………………………………………… [4] (d) Compounds D and F are isomers. What type of isomerism do they show? ………………………………………… [1] [Total: 12]

10 9701/21/O/N/09 © UCLES 2009 For Examiner’s Use 5 Three organic compounds, G, H, and J, each have the empirical formula CH2O. The numbers of carbon atoms in their molecules are shown in the table. compound number of C atoms G 1 H 2 J 3 In H and in J, the carbon atoms are bonded directly to one another. G gives a silver mirror when treated with Tollens’ reagent. H and J each give a brisk effervescence with Na2CO3(aq). (a) Identify G. ……………………………………… [1] (b) (i) What functional group is common to both H and J? ……………………………………… (ii) Identify H. ……………………………………… (iii) Identify J. ……………………………………… [3] (c) When J is heated under reflux with acidified K2Cr2O7, the product, K, gives a red-orange precipitate with 2,4-dinitrophenylhydrazine reagent. Draw the structural formula of K, the compound formed from J. [1]

11 9701/21/O/N/09 © UCLES 2009 For Examiner’s Use (d) When J is warmed with concentrated sulfuric acid, a cyclic compound, L, is formed. L has the molecular formula C6H8O4. (i) Suggest a displayed formula for L. (ii) What type of reaction occurs when L is formed from J? ……………………………………… [2] [Total: 7]

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UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2009 question paper for the guidance of teachers 9701 CHEMISTRY 9701/21 Paper 21 (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. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the October/November 2009 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 A/AS LEVEL – October/November 2009 9701 21 © UCLES 2009 1 (a) same proton number/atomic number (1) different mass number/nucleon number (1) [2] (b) Ar ( ) ( ) ( ) 100 11.29 26 10.11 25 78.60 24 × + × + × = (1) 100 2432.69 100 293.54 252.75 1886.4 = + + = which gives Ar = 24.33 (1) penalise (–1) for misuse of significant figures [2] (c) number of isotopes protons neutrons electrons 226Ra 88 138 88 238U 92 146 92 allow one mark for each correct column (3 × 1) if there are no correct columns, allow maximum one mark for a correct row [3] (d) (i) Ra2+ (1) (ii) less than (502 + 966) allow answers in the range 1000–1400 kJ mol–1 (1) ionisation energies decrease down the Group or must be less than IE for Ba → Ba2+ or size of atom increases down Group/ electrons are further away from nucleus or there is increased shielding down Group (1) allow ecf on answer to (i) [3] [Total: 10]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 21 © UCLES 2009 2 (a) (i) configuration ends in s2 or there are two electrons in outermost/valence shell (1) (ii) RaCO3/radium carbonate (1) [2] (b) anode Br – → ½Br2 + e– (1) cathode Ra2+ + 2e– → Ra (1) [2] (c) (i) water slow reaction gas bubbles gas is colourless any 2 (2) steam Mg glows vigorous reaction white solid formed any 2 (2) (ii) Mg + H2O → MgO + H2 (1) [5] (d) (i) Ra(s) + 2H2O(l) → Ra(OH)2(aq) + H2(g) eqn. (1) s.s. (1) (ii) radium dissolves/disappears gas evolved gas is colourless heat evolved any 2 (2) (iii) 10–14 (1) (iv) more – no mark for this alone because reactivity of metals increases down the Group or electrons are further from nucleus or IE is lower or Ra is a stronger reducing agent (1) [6] [Total: 15]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 21 © UCLES 2009 3 (a) (i) CH4 + Cl2 → CH3Cl + HCl –75 0 –82 –92 (1) reaction = –82 + (–92) – (–75) = –99 kJ mol–1 (1) (ii) CH4 + I2 → CH3I + HI broken C–H I–I made C–I H–I 410 151 240 299 (1) reaction = –240 + (–299) + 410 + 151 = +22 kJ mol–1 (1) (iii) activation energy is too great (1) [5] (b) (i) initiation (1) Cl2 + uvl → 2Cl (1) propagation (1) CH4 + Cl → CH3 + HCl CH3 + Cl2 → CH3Cl + Cl both needed (1) termination (1) CH3 + CH3 → C2H6 or CH3 + Cl → CH3Cl or Cl + Cl → Cl2 (1) (ii) CH3/methyl radical (1) [7]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 21 © UCLES 2009 (c) energy I Ea CH4 + Cl2 ∆H CH3Cl + HCl progress of reaction correct placement of 16 kJ (1) correct placement of –99 kJ (allow ecf on wrong calculation in (a) (i)) (1) intermediate clearly shown at I (1) correct ‘double peak’ shape (1) second peak lower than first (1) [5] [Total: max 16]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 21 © UCLES 2009 4 (a) (i) C2H5O (1) (ii) OH (1) (iii) compound type of isomerism A cis-trans or geometrical D optical allow one mark if both A and D are correctly identified but in both cases, the type of isomerism is incorrect (1 + 1) [4] (b) (i) dehydration/elimination (1) (ii) conc. H2SO4/P4O10/Al2O3/pumice etc. (1) (iii) CH2=CHCH=CH2/butadiene/buta-1,3-diene (1) [3] (c) (i) CH3CH2CH(OH)CH3 (1) (ii) steam with H3PO4 catalyst or conc. H2SO4 then water (1 + 1) (iii) Cr2O7 2– /H+ (1) [4] (d) functional group isomerism or structural isomerism not positional isomerism (1) [1] [Total: 12]

Page 7 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 21 © UCLES 2009 5 (a) G is HCHO/methanal (1) [1] (b) (i) carboxylic acid/carboxyl/–CO2H not acid (1) (ii) H is CH3CO2H/ethanoic acid (1) (iii) J is CH3CH(OH)CO2H/2-hydroxypropanoic acid allow HOCH2CH2CO2H/3-hydroxypropanoic acid (1) [3] (c) K is CH3COCO2H (1) [1] (d) (i) L is H CH3 O C O H CH3 C C O C O allow as ecf on HOCH2CH2CO2H/3-hydroxypropanoic acid CH2 O C O O C O CH2 CH2 CH2 (1) (ii) esterification allow elimination/dehydration/condensation (1) [2] [Total: 7]