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GCE JAN 2010 : (A2 3A) Synoptic Paper

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Centre Number 71 Candidate Number Assessment Unit A2 3A assessing Module 6A: Synoptic Paper [A2C31] A2C31 Chemistry *A2C31* ADVANCED General Certificate of Education January 2010 MONDAY 1 FEBRUARY, 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 six questions. Section A contains a Planning Exercise. Section B contains five questions assessing different aspects of the specification. INFORMATION INFORMATION FOR CANDIDATES The total mark for this paper is 80. Quality of written communication will be assessed in question 1. Question 1. Figures in brackets printed down the right-hand side of pages indicate the mark awarded to each question or part question. A Periodic Table of Elements (including some data) is provided. For Examiner s use only Question Number 1 2 3 4 5 6 Total Marks 5978 Marks Section A Examiner Only Marks 1 Remark Planning Exercise Plan an experiment to prepare the 2,4-dinitrophenylhydrazone derivative of propanal and then determine its melting point. NHNH2 NO2 NO2 CH3CH2CHO 2,4-dinitrophenylhydrazine propanal A solution of 2,4-dinitrophenylhydrazine is the reagent used to prepare 2,4-dinitrophenylhydrazones by reaction with aldehydes or ketones. The solution is prepared as follows: Suspend 1g of powdered 2,4-dinitrophenylhydrazine in 30 cm3 of stirred methanol and cautiously add 2 cm3 of concentrated sulphuric acid; this gives 32 cm3 of solution. Your plan should include: (a) the equation for the reaction of 2,4-dinitrophenylhydrazine with propanal; [3] (b) a calculation to show the volume of reagent required to prepare 0.2 g of the 2,4-dinitrophenylhydrazone of propanal assuming a 75% yield; [5] 5978 2 [Turn over (c) full experimental details of the recrystallisation of the 2,4-dinitrophenylhydrazone from ethanol to produce pure dry crystals and an explanation of the most important safety point to be observed; Examiner Only Marks Remark [5] (d) full experimental details of the determination of the melting point of the 2,4-dinitrophenylhydrazone; [3] 5978 3 [Turn over (e) an explanation of the use of the melting point to confirm the purity and identity of the carbonyl compound as propanal. Examiner Only Marks Remark [2] Quality of written communication 5978 [2] 4 [Turn over Section B Examiner Only Marks Remark Answer all ve questions in the spaces provided. 2 Phosphorus pentoxide is formed by the combustion of phosphorus, P4, in air or oxygen. It is a white powder which dissolves exothermically in water, eventually forming phosphoric(V) acid. (a) Calculate the volume of air, at 20 C and a pressure of one atmosphere, which is needed to convert 12.4 g of phosphorus into phosphorus pentoxide. (Assume air contains 20% oxygen by volume.) _________________________________________________________ _________________________________________________________ _________________________________________________________ ______________________________________________________ [4] (b) Phosphoric(V) acid, H3PO4, is tribasic. Write the formulae of the three sodium salts that can be formed from phosphoric acid. ______________________________________________________ [2] (c) Phosphorus pentoxide removes the elements of water from nitric acid to form nitrogen(V) oxide. Write the equation for the reaction. Do not include phosphorus pentoxide in the equation. ______________________________________________________ [1] 5978 5 [Turn over 3 Cobalt(II) ions react with nitrite ions in the presence of acid to form cobalt(III) ions together with nitrogen(II) oxide. This reaction is similar to that of iron(II) ions with nitrous acid. The cobalt(III) ion reacts with an excess of nitrite ions to form the hexanitrocobalt(III) complex ion. Examiner Only Marks Remark Co3+(aq) + 6NO2 (aq) [Co(NO2)6]3 (aq) (a) (i) Write an equation for the reaction of cobalt(II) ions with nitrite ions in the presence of hydrogen ions. [1] (ii) Draw the 3D shape of the hexanitrocobalt(III) complex ion. [1] (b) Cobalt(III) ions are stabilised in ammonium cobalt alum, NH4Co(SO4)2.12H2O, which is bright blue. (i) Calculate the percentage of cobalt in ammonium cobalt alum. [3] (ii) Write the formulae of the ions which are produced when ammonium cobalt alum is dissolved in water. [2] (iii) Describe what is observed when acidified barium ions are added to the solution. [2] 5978 6 [Turn over 4 Lithium hydride reacts with aluminium chloride to form lithal (LiAlH4) and lithium chloride. Examiner Only Marks Remark (a) (i) Write the equation for the reaction of lithium hydride with aluminium chloride. [2] (ii) Draw the dot and cross electron structure for the tetrahydridoaluminate ion (AlH4 ). [2] (iii) Draw and name the shape of the tetrahydridoaluminate ion. [2] (b) Lithal is used as a reducing agent in organic chemistry. Maleic acid, the cis form of HOOC CH CH COOH, is reduced by lithal. (i) Draw the structure of maleic acid. [1] 5978 7 [Turn over (ii) Draw the structure of fumaric acid which is the trans isomer of maleic acid. Examiner Only Marks Remark [1] (iii) When heated, maleic acid loses water to form maleic anhydride. The two COOH groups react with each other and water is eliminated. Suggest the structure of maleic anhydride. [1] (iv) Suggest why fumaric acid cannot form an anhydride. [1] (v) Draw the structure of the product from the reaction of maleic acid with an excess of lithal. [2] 5978 8 [Turn over 5 Magnesium chloride occurs in sea water and is also found as carnallite, KCl.MgCl2.6H2O. It can be prepared in the laboratory using dilute hydrochloric acid and magnesium carbonate with the product crystallising from solution as MgCl2.6H2O. Alternatively the anhydrous chloride may be prepared by combining chlorine directly with magnesium. Examiner Only Marks Remark (a) Using a diagram describe how you could prepare a sample of anhydrous magnesium chloride from magnesium and chlorine from a gas cylinder. State and explain the safety precautions to be taken. _________________________________________________________ _________________________________________________________ ______________________________________________________ [4] (b) Explain why a solution of magnesium chloride is slightly acidic. _________________________________________________________ _________________________________________________________ ______________________________________________________ [2] (c) Magnesium chloride can form a series of hydrates apart from the hexahydrate. The formula of an unknown hydrate can be determined by titrating the magnesium ions present using edta. 13.4 g of a magnesium chloride hydrate were dissolved in 1 litre of water and 25.0 cm3 samples were titrated with a 0.10 M solution of edta. The average titre was 20.0 cm3. Calculate the value of x in MgCl2.xH2O. _________________________________________________________ _________________________________________________________ ______________________________________________________ [4] 5978 9 [Turn over (d) Predict the reaction of hydrated magnesium chloride with concentrated sulphuric acid and explain the observations expected. Examiner Only Marks Remark _________________________________________________________ _________________________________________________________ ______________________________________________________ [3] (e) Describe how you could demonstrate experimentally using a silver salt that chloride ions are present in carnallite. Write an ionic equation for the reaction taking place. _________________________________________________________ _________________________________________________________ ______________________________________________________ [4] 5978 10 [Turn over 6 Propanone reacts with iodine in the presence of acid according to the equation: + CH3COCH3 + I2 CH3COCH2I + HI Examiner Only Marks Remark The rate equation for the reaction is: rate = k[ +] [CH3COCH3] (a) (i) What is the overall order of the reaction? [1] (ii) Deduce the units of k. [2] (b) The concentration of iodine can be measured as the reaction proceeds by two different methods. One is colorimetry and the other is by titrating with sodium thiosulphate. (i) Explain how you would determine the concentration of iodine by colorimetry. [4] (ii) Write the equation for the reaction of thiosulphate ions, S2O32 , with iodine and explain how you would carry out a titration to determine the concentration of iodine. Details of calculations are not required. [4] 5978 11 [Turn over (c) On the axes below sketch the graphs obtained by experiment. Examiner Only Marks [I2] Remark rate [I2] time [2] (d) Explain what the rate equation suggests about the mechanism of this reaction. _________________________________________________________ _________________________________________________________ ______________________________________________________ [2] THIS IS THE END OF THE QUESTION PAPER 5978 12 [Turn over Permission to reproduce all copyright material has been applied for. In some cases, efforts to contact copyright holders may have been unsuccessful and CCEA will be happy to rectify any omissions of acknowledgement in future if notified. 5978

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Additional Info : Gce Chemistry January 2010 Assessment Unit A2 3A Module 6A: Synoptic Paper
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