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GCE MAY 2009 : (AS 3) Practical Examination 1

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Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education 2009 Chemistry assessing Module 3: Practical Examination 1 ASC31 Assessment Unit AS 3 [ASC31] MONDAY 11 MAY, AFTERNOON TIME 2 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 four questions. Write your answers in the spaces provided. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Questions 1 and 2 are practical exercises each worth 25 marks. Question 3 is a planning exercise worth 20 marks. Question 4 is a written question testing aspects of experimental chemistry worth 20 marks. You may have access to notes, textbooks and other materials to assist you. A Periodic Table of Elements (including some data) is provided. For Examiner s use only Question Number 1 2 3 4 Total Marks 4374 Marks 1 Observation/deduction Safety goggles must be worn at all times and care must be exercised during this practical examination. Answer parts (a) and (b) of question 1. (a) You are provided with a mixture of two salts, labelled X, which have a common anion. Carry out the following experiments on X. Record your observations and deductions in the spaces below and identify the two salts. Experiment Observations Deductions (i) Describe the appearance of X. (ii) Add half a spatula-measure of X to a test tube a quarter full of water. Stir or shake the solid with the water. Add an equal volume of dilute hydrochloric acid. Add 1 cm3 of barium chloride solution. (iii) Place a half spatula-measure of X on a watch-glass and add 3 drops of concentrated hydrochloric acid. Use a clean loop of nichrome wire to place a small amount of this acidified sample of X in a blue Bunsen flame. (iv) Place a spatula-measure of X in a test tube, add 2 cm3 of dilute sodium hydroxide solution and warm gently. Test any gas evolved with damp Universal Indicator paper. Name the two salts in X ___________________________________________________ ___________________________________________________ 4374 2 [Turn over (b) You are supplied with three halobutanes labelled A, B and C. Carry out the experiment and complete the table below. Identify A, B and C. Experiment Observations A Deductions A Place 1 cm3 of A, B and C separately in three test tubes. Label B the test tubes with their contents. Add 1 cm3 of ethanol and 1 cm3 of silver nitrate solution to each test tube. Place the three test tubes in a beaker of water heated to just below boiling point. Leave for 5 minutes. C B C A is ___________________________________________________________________ B is ___________________________________________________________________ C is ________________________________________________________________[25] 4374 3 [Turn over 2 Titration (a) You are provided with: sodium hydroxide solution, 0.05 mol dm 3 vinegar solution of unknown concentration phenolphthalein indicator You are required to: (i) titrate the vinegar solution against the sodium hydroxide solution using phenolphthalein as indicator; (ii) use your results to determine the concentration of the vinegar. Procedure sodium hydroxide solution vinegar solution Rinse out a pipette with the vinegar solution. Using the pipette and pipette filler, place 25.0 cm3 of the vinegar solution in the conical flask. Rinse out a burette with the sodium hydroxide solution. Fill the burette with the sodium hydroxide solution. Add 2 or 3 drops of phenolphthalein indicator to the conical flask, and titrate until the end point is reached. Record the results of one rough and two accurate titrations in the table. Examiner Only Results Marks Initial burette reading/cm3 Final burette reading/cm3 Remark Titre/cm3 Rough 1st accurate 2nd accurate Average titre ___________ cm3 4374 [15] 4 [Turn over (b) (i) State the colour change at the end point. Examiner Only Marks Remark from ______________________ to ______________________ [1] (ii) Calculate the number of moles of sodium hydroxide used in the titration. _____________________________________________________ ___________________________________________________ [2] (iii) Write an equation for the reaction of sodium hydroxide with ethanoic acid, CH3COOH. ___________________________________________________ [2] (iv) Deduce the number of moles of ethanoic acid present in 25.0 cm3 of the vinegar solution. ___________________________________________________ [1] (v) Calculate the number of moles of ethanoic acid present in 1 dm3 of the vinegar solution. _____________________________________________________ _____________________________________________________ ___________________________________________________ [2] (vi) Convert your value of moles of ethanoic acid calculated in (v) into grams of ethanoic acid. _____________________________________________________ ___________________________________________________ [2] 4374 5 [Turn over 3 Planning Examiner Only Marks Remark You are required to plan an experiment to convert ethanol to ethene by dehydration. You are provided with the following: test tubes delivery tube water trough Bunsen burner retort stand, clamp and boss ceramic wool ethanol aluminium oxide An appropriate procedure would involve soaking some ceramic wool with ethanol and placing it in the bottom of a test tube, clamping the test tube horizontally and placing a spatula-measure of aluminium oxide half way down the tube, passing ethanol vapour over heated aluminium oxide and collecting the gas formed over water. (a) Draw a labelled diagram of how the apparatus could be arranged to carry out this reaction. [4] (b) State two weighings required to determine the mass of ethanol at the start of the experiment. _________________________________________________________ _______________________________________________________ [2] 4374 6 [Turn over (c) (i) Why is the aluminium oxide heated? Examiner Only Marks Remark ___________________________________________________ [1] (ii) Although the Bunsen burner is to be placed under the aluminium oxide, why is it occasionally used to heat the ceramic wool soaked in ethanol? _____________________________________________________ ___________________________________________________ [1] (d) Explain why the first few bubbles given off are not collected. _______________________________________________________ [1] (e) One of the main hazards in this procedure is the possibility of water being drawn back into the heated tube (suck back). (i) Explain why water may be drawn back into the heated test tube. _____________________________________________________ ___________________________________________________ [1] (ii) State what should be done if water is seen rising up the delivery tube towards the heated test tube. _____________________________________________________ ___________________________________________________ [1] 4374 7 [Turn over (f) (i) What is meant by the term dehydration? Examiner Only Marks Remark ___________________________________________________ [1] (ii) Write an equation for the dehydration of ethanol. ___________________________________________________ [1] (iii) Calculate the maximum volume of ethene which could be produced, at 20 C and 1 atmosphere pressure, if 1.30 g of ethanol was used. _____________________________________________________ ___________________________________________________ [2] (iv) Suggest why the volume of ethene collected is less than the calculated volume. ___________________________________________________ [1] (v) Describe a chemical test which would confirm that the product is an unsaturated hydrocarbon. _____________________________________________________ ___________________________________________________ [3] (vi) Explain why no ethanol is found in the sample of ethene collected over water. ___________________________________________________ [1] 4374 8 [Turn over 4 Structured Examiner Only Marks Remark An early edition of a Practical Organic Chemistry manual reported: The preparation of ethanal (b.p. 21 C). Weigh 7.5 g of sodium dichromate and place in a distillation flask with 15 cm3 of water. Fit the flask to the rest of the distillation apparatus. Mix 3 cm3 of concentrated sulphuric acid and 6 cm3 of ethanol (density = 0.79 g cm 3), adding the acid slowly, with shaking and cooling, and transfer the mixture to a tap funnel. Heat the dichromate solution to 50 C and allow the mixture in the tap funnel to run in slowly with occasional shaking. When the reaction begins, remove the flame until the vigour of the reaction subsides, then distil and collect the first 6 cm3 which will contain a mixture of ethanol, water and ethanal. (a) Ethanol is a liquid. (i) Suggest why its volume is measured rather than its mass. _____________________________________________________ ___________________________________________________ [1] (ii) Calculate the mass of ethanol used. _____________________________________________________ ___________________________________________________ [2] (b) Suggest why the procedures in the experiment are carried out slowly. _________________________________________________________ _______________________________________________________ [2] (c) If the colour remaining in the flask after the experiment has finished is orange, explain which reactant is in excess. _________________________________________________________ _______________________________________________________ [2] 4374 9 [Turn over (d) In this method the ethanal formed is not oxidised. Suggest why the experimental procedure prevents this oxidation. Examiner Only Marks Remark _______________________________________________________ [1] (e) If the ethanal is refluxed with the oxidising agent it is oxidised further. (i) Draw a diagram of a flask showing a condenser in the reflux position. There is no need to label the diagram. [2] (ii) What is the ethanal oxidised to? ___________________________________________________ [1] (f) Suggest why the distillate is best collected in a flask surrounded by ice. _________________________________________________________ _______________________________________________________ [1] 4374 10 [Turn over (g) The equation for the reaction is: 3C2H5OH + Na2Cr2O7 + 4H2SO4 3CH3CHO + 7H2O + Na2SO4 + Cr2(SO4)3 Examiner Only (i) Calculate the molar mass of ethanol. Marks Remark _____________________________________________________ ___________________________________________________ [1] (ii) Calculate the number of moles of ethanol used. ___________________________________________________ [1] (iii) If 0.1 mole of ethanal is produced calculate the percentage yield. _____________________________________________________ _____________________________________________________ ___________________________________________________ [2] (h) Suggest how you could obtain ethanal from the mixture collected at the end of the experiment. _________________________________________________________ _________________________________________________________ _______________________________________________________ [2] (i) The student, having finally obtained the distillate containing ethanal, ethanol and water added a few drops to a beaker of boiling water. Explain what would happen. _________________________________________________________ _________________________________________________________ _______________________________________________________ [2] THIS IS THE END OF THE QUESTION PAPER 4374 11 [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. 936-025-1

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Additional Info : Gce Chemistry May 2009 Assessment Unit AS 3 Module 3: Practical Examination 1
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