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GCE MAY 2006 : (A2 3A) Synoptic Paper

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Centre Number 71 Candidate Number ADVANCED General Certificate of Education 2006 Chemistry assessing Module 6A: Synoptic Paper A2C31 Assessment Unit A2 3A [A2C31] TUESDAY 6 JUNE, MORNING 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 five questions. Section A contains a Planning Exercise. Section B contains four questions assessing different aspects of the specification. For Examiner s use only INFORMATION FOR CANDIDATES The total mark for this paper is 80. Quality of written communication will be assessed in question 1. 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. Question Number 1 2 3 4 5 Total Marks A2C3AS6 2554 Marks Section A 1 Planning Exercise Preparation of nitrobenzene The following extract describes an experiment to prepare nitrobenzene (boiling point 210 C) from benzene. HNO3/H2SO4 NO2 A mixture of concentrated nitric and concentrated sulphuric acids is reacted with benzene (density 0.88 g cm 3). Place 50 g (35 cm3, 0.5 mol) of concentrated nitric acid in a round-bottomed flask, and add, with shaking, 74 g (40 cm3) of concentrated sulphuric acid. Keep the mixture cool during the addition. Add 26 g (30 cm3, 0.33 mol) of benzene in small portions; shake the flask to ensure thorough mixing after each addition. Do not allow the temperature to rise over 55 C; immerse the flask, in cold water. When all the benzene has been added, fit a reflux condenser to the flask and heat it in a water bath for 40 minutes; pour the contents of the flask into 500 cm3 of cold water; stir the mixture to wash out acid and allow to stand. When the nitrobenzene has settled, pour off the aqueous layer. Transfer the nitrobenzene to a separating funnel and shake it vigorously with 50 cm3 of water. Separate the nitrobenzene and run it into a conical flask containing 5 g of anhydrous calcium chloride. (a) Write the equation for the production of the nitronium ion, NO +, from the mixture of the 2 two concentrated acids; [2] (b) Give a statement of safety considerations; [2] (c) Calculate the volume of benzene needed to prepare 10.0 g of the nitrobenzene from benzene, assuming a 70% yield; [5] (d) Give an explanation of the following experimental details taken from the literature extract above: (i) a diagram of the chemical apparatus used for the reaction, (ii) the method of mixing the reagents, (iii) a suitable size for the round-bottomed flask , (iv) references to temperature, (v) references to drying the product. [7] (e) Give experimental detail of any additional purification of the nitrobenzene after preparation and drying. A2C3AS6 2554 2 [2] [Turn over (a) _________________________________________________________ Examiner Only Marks Remark (b) _________________________________________________________ _________________________________________________________ (c) _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ (d) _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ (e) _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Quality of written communication A2C3AS6 2554 [2] 3 [Turn over Section B Examiner Only Marks Remark Answer all four questions in the spaces provided. 2 Chrome alum has the formula KCr(SO4)2.12H2O (a) Chrome alum can be prepared by the reduction of potassium dichromate(VI) to a chromium(III) salt. (i) A suitable reducing agent is ethanol which is oxidised to ethanal. Using [O], write an equation for this oxidation. ___________________________________________________ [1] (ii) Write an equation for the conversion of the dichromate(VI) ion to the chromium(III) ion in the presence of acid. ___________________________________________________ [1] (iii) State the colour of the dichromate(VI) ion and chromium(III) ion in aqueous solution. dichromate(VI) _________________________________________ chromium(III) _______________________________________ [2] (iv) State the colour of the chrome alum crystals. ___________________________________________________ [1] A2C3AS6 2554 4 [Turn over (b) Potassium alum, KAl(SO4)2.12H2O, can be prepared in a two stage process. The first stage involves the reaction between aluminium and hot aqueous potassium hydroxide solution to form potassium aluminate. Examiner Only Marks Remark 2Al(s) + 2KOH(aq) + 6H2O(l) 2KAl(OH)4(aq) + 3H2(g) (i) Explain what safety precaution is needed in this stage. ___________________________________________________ [1] In the second stage this solution is treated with dilute sulphuric acid and potassium alum forms as crystals on cooling. (ii) Write the equation for the reaction between the potassium aluminate and sulphuric acid. ___________________________________________________ [2] A2C3AS6 2554 5 [Turn over 3 Iodine was discovered in 1812, by Courtois, who isolated it from seaweed. The method involved reaction between potassium iodide and concentrated sulphuric acid. Courtois obtained the sulphuric acid from iron(II) sulphate. The equations for the action of heat on hydrated iron(II) sulphate and the formation of sulphuric acid are: Examiner Only Marks Remark 2FeSO4.7H2O Fe2O3 + SO2 + SO3 + 7H2O SO3 + H2O H2SO4 (a) (i) Deduce the oxidation state of iron in FeSO4.7H2O and in Fe2O3. FeSO4.7H2O ____________________ Fe2O3 ____________________ [2] (ii) Calculate the maximum mass of sulphuric acid obtainable from 55.6 g of hydrated iron(II) sulphate. ______________________________________________________ ______________________________________________________ ______________________________________________________ ___________________________________________________ [3] (b) (i) Today, sulphuric acid is made by the Contact process. Name the catalyst used in this process. ___________________________________________________ [1] (ii) Write the equation for the conversion of sulphur dioxide to sulphur trioxide. ___________________________________________________ [1] A2C3AS6 2554 6 [Turn over (c) (i) Using the electrode potentials given below, explain why the addition of potassium iodide solution to dilute sulphuric acid does not, in theory, produce iodine. Examiner Only Marks Remark E /V I2(aq) + 2e 2I (aq) 0.54 SO42 (aq) + 4H+(aq) + 2e H2SO3(aq) + H2O(l) 0.20 MnO4(aq) + 8H+(aq) + 5e Mn2+(aq) + 4H2O(l) 1.51 ______________________________________________________ ___________________________________________________ [1] (ii) Explain why addition of potassium manganate(VII) causes iodine to form. ______________________________________________________ ___________________________________________________ [1] (d) Iodine reacts reversibly with benzene to form iodobenzene. Iodobenzene can also be prepared by reaction between benzene diazonium ions and potassium iodide. N+ + I + 2 I + N2 (i) Explain, giving practical details, how benzene diazonium ions may be prepared in the laboratory. ______________________________________________________ ______________________________________________________ ______________________________________________________ ___________________________________________________ [3] A2C3AS6 2554 7 [Turn over (ii) Explain how the rate of formation of iodobenzene may be determined using the nitrogen given off during the reaction. Examiner Only Marks Remark ______________________________________________________ ______________________________________________________ ______________________________________________________ ___________________________________________________ [3] (iii) State the overall order of the reaction if the rate equation is: rate = k[C6H5N 2+]1[I ]0 ___________________________________________________ [1] (iv) If the rate constant for the reaction is 0.105 s 1 at 10 C calculate the rate of reaction if the concentration of benzene diazonium ions is 0.066 mol dm 3. ___________________________________________________ [1] A2C3AS6 2554 8 [Turn over 4 Kalman, writing in Medicine and Science in Sports and Exercise claimed that a commercial preparation containing creatine, sucrose, taurine, and lipoic acid significantly affected body composition and muscle endurance. Taurine S NH2 CH2 CH2 NH2 HN C O Lipoic acid CH2OH O CH2OH OH H OH H OH H OH CH2 H CH2 OH O H NCH2COOH CH3 Sucrose H Remark Creatine O HO Examiner Only Marks CH2OH CH(CH2)4COOH SS OH H (a) Sucrose is a disaccharide which can be hydrolysed to form fructose and glucose. (i) Explain the term hydrolysed and write an appropriate equation, representing sucrose by C6H11O5 O C6H11O5 ______________________________________________________ ___________________________________________________ [2] (ii) State what is observed when fructose and glucose are heated with Fehling s solution. Explain any change taking place. ______________________________________________________ ______________________________________________________ ___________________________________________________ [3] A2C3AS6 2554 9 [Turn over (b) Creatine is an amino acid. Examiner Only Marks Remark (i) Explain why creatine is very soluble in water. ______________________________________________________ ___________________________________________________ [2] (ii) Explain why, unlike alanine, creatine is not optically active. ______________________________________________________ ___________________________________________________ [1] (iii) Suggest an equation for the reaction between creatine and sodium hydrogencarbonate. ___________________________________________________ [2] (iv) Write an equation for the reaction between creatine and taurine to form a dipeptide containing a peptide link. ___________________________________________________ [2] A2C3AS6 2554 10 [Turn over (c) In March 1997, Franklin Leach described the reaction between lipoic acid and enzymes. He used the reaction to elucidate the primary and secondary structure of an enzyme. Examiner Only Marks Remark (i) Explain the term primary structure. ______________________________________________________ ___________________________________________________ [2] (ii) Explain the effect of increasing the temperature from 25 to 60 C on the activity of a typical enzyme. ______________________________________________________ ___________________________________________________ [2] (iii) State the term used to describe the mechanism of enzyme action. ___________________________________________________ [1] A2C3AS6 2554 11 [Turn over 5 (a) The mass spectrum of ethyl ethanoate is shown below. Examiner Only Marks Remark 100 relative intensity 80 60 40 20 0 10 20 30 40 50 60 mass/charge 70 80 90 State the molecular ions responsible for the peaks at: 45 _______________________________________________________ 88 ____________________________________________________ [2] (b) The nuclear magnetic resonance spectrum of ethyl ethanoate is shown below: Integration curve 10 9 8 7 6 5 4 3 2 1 0 ppm A2C3AS6 2554 12 [Turn over (i) Name the substance responsible for the peak at 0 ppm. Examiner Only Marks Remark ___________________________________________________ [1] (ii) Explain why there are three other sets of peaks. ___________________________________________________ [1] (iii) Explain why the signal at 4.1 ppm has the highest shift. ______________________________________________________ ___________________________________________________ [2] (iv) Explain the term integration curve. ___________________________________________________ [1] (v) Use the integration curve and splitting patterns to identify the hydrogen atoms responsible for the three signals. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ___________________________________________________ [3] A2C3AS6 2554 13 [Turn over (c) The infrared spectrum for ethyl ethanoate is given below and the peak corresponding to C H is mapped ( ) onto the correct frequency. Carry out a similar mapping for the covalent bonds C O and C O in ethyl ethanoate. [2] 4000 3000 RO RN H H Wave number, cm 1 2000 1500 2500 1300 1200 1100 O C R C H R CO R CC H CC CC H 3 N C 4 4000 3000 2500 3 C C 4 5 2000 1500 5 6 7 6 Wave number, cm 1 13001200 1100 1000 8 9 10 Wavelength microns 7 8 800 900 11 12 9 700 13 14 15 The infrared spectrum for ethyl ethanoate A2C3AS6 2554 14 [Turn over (d) 200.0 g of ethyl ethanoate and 7.0 g of water were refluxed together. At equilibrium, the mixure contained 0.31 mol of ethanoic acid. CH3COOCH2CH3(l) + H2O(l) Examiner Only Marks Remark CH3COOH(l) + CH3CH2OH(l) (i) Write an expression for Kc. ___________________________________________________ [1] (ii) Calculate Kc. ______________________________________________________ ______________________________________________________ ___________________________________________________ [2] (iii) Deduce the value of Kc for the reverse reaction. ___________________________________________________ [1] (iv) The rate of this reaction can be increased using homogeneous acid catalysis. Explain the term homogeneous. ______________________________________________________ ___________________________________________________ [1] (v) State the effect, if any, of the catalyst on the equilibrium constant, Kc. ___________________________________________________ [1] THIS IS THE END OF THE QUESTION PAPER A2C3AS6 2554 15 [Turn over S 2/06 4300 302507(165) [Turn over

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Additional Info : Gce Chemistry June 2006 Assessment Unit A2 3A Module 6A: Synoptic Paper
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