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GCE MAY 2008 : (A2 2) Analytical, Transition Metals and Further Organic Chemistry

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Centre Number 71 Candidate Number ADVANCED General Certificate of Education 2008 Chemistry assessing Module 5: Analytical, Transition Metals and Further Organic Chemistry A2C21 Assessment Unit A2 2 [A2C21] WEDNESDAY 28 MAY, AFTERNOON TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all sixteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all six questions in Section B. Write your answers in the spaces provided in this question paper. For Examiner s use only Question Number Marks Section A 1 10 INFORMATION FOR CANDIDATES The total mark for this paper is 90. Quality of written communication will be assessed in question 14(a)(iii). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided. A2C2S8 3539 Section B 11 12 13 14 15 16 Total Marks BLANK PAGE A2C2S8 3539 2 [Turn over Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following is the electronic structure for the iron(III) ion in the ground state? A B C D 2 Which one of the following is the spin-spin splitting pattern in the n.m.r. spectrum of ethyl ethanoate? A B C D 3 1s22s22p63s23p63d5 1s22s22p63s23p64s13d4 1s22s22p63s23p64s13d5 1s22s22p63s23p64s23d3 singlet, doublet, triplet singlet, quartet, triplet triplet, doublet, triplet triplet, quartet, triplet Which one of the following peaks in the mass spectrum of pentane is the base peak? B relative abundance A 10 A2C2S8 3539 20 30 C D 40 50 60 70 3 m/e [Turn over 4 Which one of the following is the strongest base? A B C D 5 NH3 NH4+ CH3NH2 CH3NH3+ Which one of the following molecules contains a chromophore? O A C H O B C N O N Which one of the following analytical techniques depends upon vibrational frequencies of bonds? A B C D 7 NH2 D 6 C infra-red spectroscopy n.m.r. spectroscopy u.v. spectroscopy visible spectroscopy In the complex ion, [MCl2(NH3)4]+, which one of the following is the identity of M and its associated oxidation state? A B C D A2C2S8 Ag Cu Cr Mn 3539 +1 +2 +3 +7 4 [Turn over 8 The mechanism for the conversion of benzene to nitrobenzene is described as A B C D 9 electrophilic addition. electrophilic substitution. free radical substitution. nucleophilic addition. A sample of sodium chlorate(V) on heating produced 120 cm3 of oxygen, measured at 20 C and one atmosphere pressure. 2NaClO3(s) 2NaCl(s) + 3O2(g) How many moles of sodium chlorate(V) decomposed? A B C D 0.167 10 3 mol 0.250 10 3 mol 1.67 10 3 mol 3.33 10 3 mol 10 Using the infra-red absorption frequencies, C H C=O O H C O broad 2853 2962 cm 1 strong 1680 1750 cm 1 strong 2500 3300 cm 1 strong 1200 1400 cm 1 it is possible to identify the following spectrum: 100 transmittance (%) C 0 4000 3000 2000 1500 1000 500 wave-number (cm 1) as that of A B C D A2C2S8 ethanoic acid. ethanol. propan-1-ol. propanone. 3539 5 [Turn over Section B Examiner Only Marks Remark Answer all six questions in the spaces provided. 11 A mixture of concentrated nitric and sulphuric acids forms a nitrating mixture, which is used to nitrate benzene. H2SO4 + HNO3 NO2 + H2O (a) Write the equation for the reaction between nitric acid and sulphuric acid to form a nitronium ion. ______________________________________________________ [2] (b) Explain how nitric acid is acting as a Br nsted base in this reaction. ______________________________________________________ [1] (c) Explain why sulphuric acid may be regarded as a catalyst in this reaction. _________________________________________________________ ______________________________________________________ [1] A2C2S8 3539 6 [Turn over 12 The chelating ligand edta has the following structure: Examiner Only Marks Remark O C OH H2C O N HO C CH2 CH2 CH2 CH2 N O C OH CH2 HO C O (a) Explain the term chelating and state the shape of the complex which edta forms with magnesium ions. _________________________________________________________ ______________________________________________________ [2] (b) Explain how standard edta solution may be used to determine the concentration of magnesium ions in solution, naming the indicator and stating the colour change. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ ______________________________________________________ [4] A2C2S8 3539 7 [Turn over 13 The determination of iron in its ores is an example of the application of manganate(VII) titrations. Before titration with manganate(VII) ions any iron(III) must be reduced to iron(II). This reduction can be carried out with zinc amalgam (a mixture of zinc and mercury). Zn2+(aq) + 2e Zn(s) Fe(s) E = 0.44 V Fe3+(aq) + e Fe2+(aq) Remark E = 0.76 V Fe2+(aq) + 2e Examiner Only Marks E = +0.77 V (a) (i) Write the equation for the reaction between zinc and iron(III) ions. __________________________________________________ [1] (ii) The use of the zinc amalgam prevents the further reduction of iron(II) to iron. Use the electrode potentials above to explain why, in theory, zinc would also reduce iron(II) to iron. _____________________________________________________ __________________________________________________ [1] (b) A mixture of iron(II) and iron(III) sulphates was analysed as described above. The mixture was dissolved in water and made up to 1.0 dm3. It was found that 25.0 cm3 of this solution needed 21. 6 cm3 of 0.1 M acidified potassium manganate(VII) solution to reach the end point. After reduction of a separate 25.0 cm3 of the solution by zinc amalgam, 22.8 cm3 of the 0.1 M acidified potassium manganate(VII) solution were required. (i) What colour change is observed at the end point? __________________________________________________ [2] (ii) Write the equation for the reaction between iron(II) ions and acidified manganate(VII) ions. __________________________________________________ [2] A2C2S8 3539 8 [Turn over (iii) Using the first titration figure, calculate the number of moles of iron(II) ions present in the 1.0 dm3 solution. Examiner Only Marks Remark _____________________________________________________ __________________________________________________ [1] (iv) What mass of iron(II) sulphate was present in the mixture? __________________________________________________ [1] (v) Using the second titration figure, calculate the total mass of iron(III) sulphate present in the mixture. _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [3] A2C2S8 3539 9 [Turn over 14 The transport of some proteins through the body may be assisted by cobalt(II) ions. Examiner Only Marks Remark (a) (i) Protein structure is described as primary, secondary or tertiary. Explain these terms. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [3] (ii) Name two functional groups in a protein which allow it to bond to metal ions such as cobalt(II). _____________________________________________________ __________________________________________________ [2] (iii) Hydrolysis of proteins yields amino acids which can be separated by two-way chromatography. Explain how two-way chromatography could be used to separate a mixture of the four amino acids glycine, alanine, threonine and leucine. Describe how the presence of leucine in the mixture could be confirmed. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [4] Quality of written communication A2C2S8 A2C2S8 3539 [2] 10 [Turn over (b) Threonine has a zwitterion (dipolar ion) structure. Examiner Only Marks Remark CH3 CH +H N 3 OH CH C O O (i) Explain the term chiral and mark any chiral centres in threonine with an asterisk (*). _____________________________________________________ __________________________________________________ [3] (ii) Explain how the zwitterion (dipolar ion) is formed. __________________________________________________ [1] (iii) Explain why threonine has a high melting point. _____________________________________________________ __________________________________________________ [2] (iv) Write an equation for the reaction between threonine and nitrous acid. __________________________________________________ [2] (v) Suggest what will be observed if a solution of threonine is added to nitrous acid. __________________________________________________ [1] A2C2S8 A2C2S8 3539 11 [Turn over [Turn over 15 Amines may be prepared by the reduction of nitriles or by the reaction of ammonia with alkyl halides. Examiner Only Marks Remark (a) 1-bromobutane reacts with ammonia (by a similar mechanism to that of the alkaline hydrolysis of haloalkanes) to form 1-aminobutane. (i) Name the mechanism. __________________________________________________ [1] (ii) Write an equation for the reaction. __________________________________________________ [1] (iii) Describe the mechanism for the reaction. _____________________________________________________ _____________________________________________________ __________________________________________________ [3] (b) 1-aminobutane may also be prepared by the reduction of butanenitrile. (i) Name a suitable reducing agent. __________________________________________________ [1] (ii) Using [H] to represent the reducing agent write an equation for the reduction of butanenitrile. __________________________________________________ [2] A2C2S8 A2C2S8 3539 12 [Turn over (c) Nitriles may undergo acid or base catalysed hydrolysis. Examiner Only Marks Remark (i) Explain the term hydrolysis. _____________________________________________________ __________________________________________________ [1] (ii) Draw a labelled enthalpy level diagram, using the axes below, to illustrate the uncatalysed and the acid catalysed hydrolysis of butanenitrile. Assume the reaction is exothermic. [3] (iii) Write the equation for the reaction of butanenitrile with aqueous sodium hydroxide. __________________________________________________ [2] A2C2S8 A2C2S8 3539 13 [Turn over 16 Malachite has the formula CuCO3.Cu(OH)2, and can be readily converted to copper(II) oxide by heating. The oxide can be reduced to copper by heating strongly with carbon. Examiner Only Marks Remark (a) (i) What is the percentage of copper in malachite? _____________________________________________________ _____________________________________________________ __________________________________________________ [3] (ii) Write an equation for the action of heat on malachite. __________________________________________________ [2] (iii) Write an equation for the reduction of copper(II) oxide by carbon. __________________________________________________ [1] (b) Malachite dissolves in nitric acid to form copper(II) nitrate solution. The dropwise addition of excess ammonia solution produces colour changes. (i) State and explain the observations on adding ammonia solution, giving the formulae of the copper compounds or complex(es) formed. _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [4] A2C2S8 A2C2S8 3539 14 [Turn over (ii) State and explain the colour change observed on adding concentrated hydrochloric acid to the final solution in part (i), giving the formula of the copper complex formed. Examiner Only Marks Remark _____________________________________________________ __________________________________________________ [2] (iii) Explain these ligand replacement reactions in terms of the overall stability constants. _____________________________________________________ _____________________________________________________ __________________________________________________ [3] THIS IS THE END OF THE QUESTION PAPER A2C2S8 A2C2S8 3539 15 [Turn over S 4/07 529-025-1 [Turn over

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Additional Info : Gce Chemistry May 2008 Assessment Unit A2 1Module 5: Analytical, Transition Metals and Further Organic Chemistry
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