Cambridge A Level Chemistry 9701 — 2006 May/June Paper 2 · Variant 1

This document consists of 11 printed pages and 1 blank page. SP (CW) T15741/2 © UCLES 2006 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level CHEMISTRY Paper 2 Structured Questions AS Core 9701/02 May/June 2006 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 in the spaces provided on the Question Paper. You may use a pencil for any diagrams, graphs, or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. 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. You may use a calculator. 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. DO NOT WRITE IN THE BARCODE. DO NOT WRITE IN THE GREY AREAS BETWEEN THE PAGES. For Examiner’s Use 1 2 3 4 5 Total

2 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use Answer all the questions in the spaces provided. 1 Mohr’s salt is a pale green crystalline solid which is soluble in water. Mohr’s salt is a ‘double salt’ which contains two cations, one of which is Fe2+, one anion which is SO4 2–, and water of crystallisation. (a) The identity of the second cation was determined by the following test. Solid Mohr’s salt was heated with solid sodium hydroxide and a colourless gas was evolved. The gas readily dissolved in water giving an alkaline solution. (i) What is the gas? … (ii) What is the formula of the second cation identified by this test? … (iii) In this test, a grey/green solid residue was also formed. Suggest a name or formula for this solid. … [3] (b) The identity of the anion present in Mohr’s salt was confirmed by adding dilute hydrochloric acid followed by aqueous barium chloride to an aqueous solution of Mohr’s salt. A white precipitate was formed. Suggest the identity of the white precipitate. …[1] (c) When a double salt such as Mohr’s salt is made, the two individual salts are mixed together in a 1:1 molar ratio, dissolved in water and the solution crystallised. (i) Give the formula of each of the two salts that would be mixed to make the double salt, Mohr’s salt. salt 1 … salt 2 …

3 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use [Turn over (ii) Calculate the relative formula mass of each of the salts present in Mohr’s salt. salt 1 relative formula mass of salt 1 … salt 2 relative formula mass of salt 2 … (iii) The crystals of the double salt contain water of crystallisation. The relative formula mass of Mohr’s salt is 392. Use your answers to (ii) to calculate the number of moles of water of crystallisation present in one mole of Mohr’s salt. [6] [Total: 10]

4 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use 2 The unsaturated hydrocarbon ethyne (acetylene), C2H2, is widely used in ‘oxy-acetylene torches’ for cutting and welding metals. In the torch, ethyne is burned in oxygen to produce a flame with a temperature of 3400 K. (a) Ethyne is a linear molecule with a triple bond, C
C, between the two carbon atoms. Draw a ‘dot-and-cross’ diagram of an ethyne molecule. [1] (b) When used for cutting or welding, ethyne is transported in cylinders which contain the gas under pressure. A typical cylinder has a volume of 76 dm3 and contains ethyne gas at 1515 kPa pressure at a temperature of 25 °C. Use the general gas equation, pV = nRT, to calculate the amount, in moles, of ethyne in this cylinder. [2] (c) In some countries, ethyne is manufactured from calcium carbide, CaC2, which is produced by heating quicklime and coke together at 2300 K. CaO + 3C CaC2 + CO When water is added to the CaC2, calcium hydroxide, Ca(OH)2, and ethyne, C2H2, are produced. (i) Construct a balanced equation for the formation of ethyne from calcium carbide. … (ii) Use this equation and your answer to part (b) to calculate the mass of CaC2 which will react with an excess of water to produce enough ethyne to fill 100 cylinders of the gas. [3]

5 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use [Turn over (d) The equation for the complete combustion of ethyne is given below. Use appropriate bond energy data from the Data Booklet to calculate a value for the enthalpy change of combustion of ethyne. C2H2(g) + ⁵⁄₂O2(g) 2CO2(g) + H2O(g) [3] (e) The value for the standard enthalpy change of combustion of ethyne is –1300 kJ mol–1. (i) Define the term standard enthalpy change of combustion. … … … (ii) Explain why your answer to (d) does not have the same value as the standard enthalpy change of combustion. … … [3] [Total: 12]

6 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use 3 This question is about the elements of Group VII, the halogens. (a) Complete the following table. halogen colour physical state at room temperature chlorine bromine iodine [2] (b) Concentrated sulphuric acid is added to separate solid samples of magnesium chloride, magnesium bromide, and magnesium iodide. (i) Describe, in each case, one observation you would be able to make. MgCl2 … … MgBr2 … … MgI2 … … (ii) Give an equation for the reaction of concentrated sulphuric acid with magnesium chloride. … [4] (c) When dilute nitric acid and aqueous silver nitrate are added to a solution of a magnesium halide, MgX2, a pale cream precipitate is formed. This precipitate is soluble in concentrated aqueous ammonia but not soluble in dilute aqueous ammonia. (i) What is the identity of the precipitate? … (ii) Give an equation, with state symbols, for the reaction of the precipitate with concentrated aqueous ammonia. … [3]

7 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use [Turn over (d) A hot glass rod is plunged into separate gas jars, one containing hydrogen chloride and one containing hydrogen iodide. (i) For each gas, state what you would observe, if anything, and write an equation for any reaction that takes place. HCl … … HI … … (ii) Explain your answer to (i) in terms of enthalpy changes. … … … (iii) What is the role of the hot glass rod in any reaction that occurs? … … [6] [Total: 15]

8 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use 4 Compounds containing the allyl group, CH2=CHCH2− , have pungent smells and are found in onions and garlic. Allyl alcohol, CH2=CHCH2OH, is a colourless liquid which is soluble in water. (a) Allyl alcohol behaves as an alkene and as a primary alcohol. Give the structural formula of the organic compound formed when allyl alcohol is (i) reacted with Br2, (ii) heated under reflux with an acidified solution of Cr2O7 2– ions. [2] (b) When allyl alcohol is reacted with MnO2 at room temperature, propenal, CH2=CHCHO is formed. What type of reaction is this? …[1] (c) Allyl alcohol may be converted into propanal, CH3CH2CHO, by using a ruthenium(IV) catalyst in water. CH2=CHCH2OH ruthenium(IV) catalyst CH3CH2CHO The reactant and the product are isomers. What form of isomerism do they display? …[1]

9 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use [Turn over (d) Allyl alcohol can be converted into propanal in two steps without the use of a ruthenium(IV) catalyst. CH2=CHCH2OH step I CH3CH2CH2OH step II CH3CH2CHO What reagents and conditions would be used for each step? step I reagent(s) … condition(s) … step II reagent(s) … condition(s) …[4] (e) By considering your answers to (b) and (d), suggest what is unusual about the single- step reaction in (c). … …[1] (f) Suggest the structural formula of the organic compound formed when allyl alcohol is (i) reacted with cold, dilute MnO4 – ions, (ii) heated under reflux with acidified MnO4 – ions. [3] [Total: 12]

10 9701/02/M/J/06 © UCLES 2006 For Examiner’s Use 5 Many organic reactions are substitution reactions in which the number of carbon atoms in the organic compound is unchanged. (a) What is meant by the term substitution reaction? … …[1] (b) One example of a substitution reaction is the formation of an alcohol from a halogenoalkane. (i) Write a balanced equation for the formation of ethanol from bromoethane. … (ii) State the conditions for this reaction. …[2] (c) In a few organic reactions, the product contains one more carbon atom than the starting material. (i) Write the equation for a reaction in which the organic compound bromoethane, which contains two carbon atoms, is converted into an organic compound which contains three carbon atoms. … (ii) State the conditions for this reaction. …[2]

11 9701/02/M/J/06 (d) Ethanol may be converted into propanoic acid in a three-stage process which uses ethanol as the only organic compound. C2H5OH step I K step II L step III C2H5CO2H (i) Give the structural formulae of the intermediate compounds K and L. K … L … (ii) State the reagent(s) used and give the essential condition(s) for step I and for step III. step I reagent(s) … condition(s) … step III reagent(s) … condition(s) … [6] [Total: 11]

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Level and GCE Advanced Subsidiary Level MARK SCHEME for the May/June 2006 question paper 9701 CHEMISTRY 9701/02 Paper 2 Maximum raw mark 60 This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which Examiners were initially instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. Any substantial changes to the mark scheme that arose from these discussions will be recorded in the published Report on the Examination. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes must be read in conjunction with the question papers and the Report on the Examination. The minimum marks in these components needed for various grades were previously published with these mark schemes, but are now instead included in the Report on the Examination for this session. • CIE will not enter into discussion or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the May/June 2006 question papers for most IGCSE and GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 1 Mark Scheme Syllabus Paper GCE A/AS Level – May/June 2006 9701 02 © University of Cambridge International Examinations 2006 1 (a) (i) ammonia/NH3 (1) (ii) NH4 + (1) (iii) iron(II) hydroxide/Fe(OH)2 (1) [3] (b) barium sulphate/BaSO4 (1) [1] (c) (i) FeSO4 (1) (NH4)2SO4 (1) (ii) FeSO4 = 151.9 (allow 151.8 to 152) (1) (NH4)2SO4 = 132.1 (allow 132) (1) (iii) xH2O = 392 – (132.1 + 151.9) = 108 (1) x = 108 = 6 (1) 18 allow e.c.f. on candidate’s sulphate in (c)(i) e.c.f. answer must be a whole number [6] [Total: 10]

Page 2 Mark Scheme Syllabus Paper GCE A/AS Level – May/June 2006 9701 02 © University of Cambridge International Examinations 2006 2 (a) x o Hx oCx oCo xH x o (1) [1] (b) n = PV = (1515 x 103) x (76 x 10-3) (1) RT 8.31 x 298 = 46.5 (1) [2] (c) (i) CaC2 + 2H2O → Ca(OH)2 + C2H2 (1) (ii) n(C2H2) = n(CaC2) =100 x 46.5 (1) mass of CaC2 = 100 x 46.5 x 64 = = 297 570 g = 297.6 kg (accept 298 kg) correct units necessary (1) allow e.c.f. on candidate’s answer in (b) [3] (d) C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(g) bonds broken: 2(H-C) 2 x 410 = 820 C≡C 840 = 840 5/2(O=O) 5/2 x 496 = 1240 2900 kJ mol-1 (1) bonds made: 4(C=O) 4 x 740 = 2960 2(O-H) 2 x 460 = 920 3880 kJ mol-1 (1) ∆Hcomb = -3880 + 2900 = -980 kJ mol-1 (1) allow e.c.f. on incorrect bonds made/broken [3] (e) (i) the enthalpy/energy change when one mole of a substance (1) is burned in an excess of air/oxygen or completely combusted under standard conditions (1) (ii) calculation in (d) includes H2O(g) whereas ∆Hcomb involves H2O(l) or average bond energy terms are used in the Data Booklet (1) [3] [Total: 12]

Page 3 Mark Scheme Syllabus Paper GCE A/AS Level – May/June 2006 9701 02 © University of Cambridge International Examinations 2006 3 (a) halogen colour physical state at room temperature chlorine green/yellow gas bromine orange/red liquid iodine black solid three colours correct (1) three states correct (1) [2] (b) (i) MgCl2 white fumes/steamy fumes (of HCl) (1) MgBr2 red colour (of Br2) or steamy fumes (of HBr) (1) MgI2 purple colour (of I2) or black solid (I2) or yellow solid (S) or stinking gas (H2S) (1) (ii) MgCl2 + H2SO4 → MgSO4 + 2HCl allow MgCl2 + 2H2SO4 → Mg(HSO4)2 + 2HCl (1) [4] (c) (i) AgBr/silver bromide (1) (ii) AgBr(s) + 2NH3(aq) → Ag(NH3)2Br(aq) equation (may be ionic) (1) state symbols (1) allow ecf on wrong halide in (i) [3] (d) (i) HCl no reaction (1) HI purple vapour/black solid (1) 2HI → H2 + I2 (1) (ii) bond energy in HCl is high (1) bond energy in HI is lower/more easily broken (1) (iii) hot glass rod provides activation energy (1) [6] [Total: 15]

Page 4 Mark Scheme Syllabus Paper GCE A/AS Level – May/June 2006 9701 02 © University of Cambridge International Examinations 2006 4 (a) (i) BrCH2CHBrCH2OH (1) (ii) CH2=CHCO2H (1) [2] (b) oxidation (1) [1] (c) structural or functional group isomerism (1) [1] (d) step I CH2=CHCH2OH → CH3CH2CH2OH H2 (1) Ni catalyst and heat or Pt at room temperature (1) step II CH3CH2CH2OH → CH3CH2CHO acidified dichromate(VI) (1) heat not under reflux or distil off aldehyde as it is formed (1) for both steps, conditions mark is only awarded if correct reagent is given [4] (e) both oxidation and reduction have occurred (1) [1] (f) (i) HOCH2CHOHCH2OH formed CH2=CH- forms HOCH2CHOH- (1) -CH2OH is unchanged (1) (ii) HO2CCO2H (1) [3] [Total: 12]

Page 5 Mark Scheme Syllabus Paper GCE A/AS Level – May/June 2006 9701 02 © University of Cambridge International Examinations 2006 5 (a) A reaction in which one atom or group of atoms replaces another. (1) [1] (b) (i) C2H5Br + NaOH → C2H5OH + NaBr allow OH- (1) (ii) heat with aqueous NaOH/OH- (1) [2] (c) (i) C2H5Br + KCN → C2H5CN + KBr allow CN- or NaCN (1) (ii) heat with KCN under reflux in ethanol (1) [2] (d) (i) K is C2H5Cl/C2H5Br/C2H5I (1) L is C2H5CN (1) (ii) step I reagent - PCl3 or PCl5 or SOCl2 or NaBr +conc H2SO4 or P + Br2 or P + I2 (1) conditions - room temperature or heat under reflux depending on reagent (1) step III reagent - mineral acid (1) conditions - heat under reflux (1) for both steps, conditions mark is only awarded if correct reagent is given [6] [Total: 11]