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GCE MAY 2006 : (AS 3) Practical Examination 1

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Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education 2006 Chemistry assessing Module 3: Practical Examination 1 ASC31 Assessment Unit AS 3 [ASC31] WEDNESDAY 17 MAY, MORNING TIME 2 hours 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 material 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 ASC3S6 1814 Marks 1 Observation/deduction Safety goggles must be worn at all times and care should be exercised during this practical examination. (a) You are provided with a mixture of two salts, labelled A, which have a common cation. Carry out the following experiments on the mixture. Record your observations and deductions in the spaces below and identify the two salts. Experiment Observations Deductions 1 Describe the appearance of A. 2 (a) Place a half spatula-measure of A on a watch-glass and add 3 drops of concentrated hydrochloric acid. (b) Use a clean loop of nichrome wire to place a small amount of this acidified sample of A in a blue Bunsen flame. 3 (a) Place a half spatula-measure of A in a test tube and add about 1 cm3 of dilute nitric acid. (b) Identify the gas evolved using a suitable reagent. 4 (a) Make up a solution of A by dissolving a half spatulameasure of A in a test tube half full of dilute nitric acid. Put 1 cm3 each of the solution into two separate test tubes. (b) (i) Add an equal volume of magnesium nitrate solution to one test tube (ii) Add 5 drops of dilute nitric acid and 1 cm3 of barium chloride solution to the other test tube. Name the two salts in A ____________________________________________ ASC3S6 1814 ____________________________________________ 2 [Turn over (b) You are supplied with three halobutanes labelled P, Q and R. Carry out the experiment and complete the table below. Identify P, Q and R. Experiment Observations Deductions P Q Q R Place 1 cm3 of P, Q and R separately, into three test tubes. Label 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. P R P is __________________________ Q is __________________________ R is __________________________ ASC3S6 1814 [25] 3 [Turn over 2 Titration (a) You are provided with: sodium thiosulphate solution of concentration 0.05 mol dm 3 a solution containing 1.90 g dm 3 of impure potassium iodate(V). solid potassium iodide (4 1.5 g portions) starch indicator sulphuric acid of concentration 1.0 mol dm 3 You are required to: (i) add the potassium iodide to the potassium iodate(V) solution, acidify the solution and titrate the liberated iodine with the sodium thiosulphate solution. (ii) use your results to determine the percentage purity of the potassium iodate(V). Procedure sodium thiosulphate solution potassium iodate(V) potassium iodide sulphuric acid ASC3S6 1814 Rinse out a burette with the sodium thiosulphate solution. Fill the burette with the sodium thiosulphate solution. Rinse out the pipette with the potassium iodate(V) solution. Using the pipette and a pipette filler, place 25.0 cm3 of the potassium iodate(V) solution in the conical flask. Add 1.5 g of potassium iodide to the conical flask and swirl to dissolve. Add about 10 cm3 of 1.0 mol dm 3 sulphuric acid to the conical flask. Add the sodium thiosulphate solution from the burette until the mixture is pale yellow; add starch indicator and then continue adding the sodium thiosulphate solution until the end point is reached. Record the results of one rough and two accurate titrations in the table. 4 [Turn over Results Examiner Only Marks Initial burette reading/cm3 Final burette reading/cm3 Remark Titre/cm3 Rough 1st accurate 2nd accurate Average titre ___________ cm3 [15] (b) State the colour change observed at the end point of the titration. from __________________ to __________________ [1] (c) The equation for the reaction between iodate(V) ions and acidified iodide ions is: IO (aq) + 5I (aq) + 6H+(aq) 3I2(aq) + 3H2O(l) 3 The equation for the reaction between the thiosulphate ions and iodine is: 2S2O2 (aq) + I2(aq) S4O2 (aq) + 2I (aq) 3 6 (i) Complete the mole ratio: IO 3 mole ratio : 1 : I2 : S2O2 3 : [1] (ii) Calculate the number of moles of sodium thiosulphate in the average titre. ______________________________________________________ ____________________________________________________ [2] ASC3S6 1814 5 [Turn over (iii) Use the mole ratio to determine the number of moles of potassium iodate(V) present in 25.0 cm3 of solution. Examiner Only Marks Remark ____________________________________________________ [1] (iv) Calculate the number of moles of potassium iodate(V) present in 1.0 dm3 of solution. ____________________________________________________ [1] (v) Calculate the mass of potassium iodate(V) in 1.0 dm3 of solution. ______________________________________________________ ____________________________________________________ [2] (vi) Determine the percentage purity of the potassium iodate(V). ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] ASC3S6 1814 6 [Turn over BLANK PAGE (Questions continue overleaf) ASC3S6 1814 7 [Turn over 3 Planning Examiner Only Marks Remark The viscosity of polyhydric alcohols is an indication of the number of OH groups present. CH3CH2OH CH2OHCH2OH CH2OHCHOHCH2OH ethanol glycol glycerol The viscosity of liquids can be compared by measuring the flow rates (cm3 s 1). This may be carried out using a burette measuring the volume of liquid flowing from the burette using a timing device (a) (i) Draw a labelled diagram showing how the flow rate could be determined. [2] (ii) Explain how you would use the measurements from the experiment to determine the flow rate in cm3 s 1. ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] ASC3S6 1814 8 [Turn over (b) The flow rate can also be represented in mol min 1. Calculate the molar flow rate of ethanol (density 0.8 g cm 3) if the flow rate, as determined by experiment, was 2.6 cm3 s 1. Examiner Only Marks Remark Flow rate in cm3 min 1. _______________________________________________________ [1] Flow rate in g min 1. _______________________________________________________ [1] Flow rate in mol min 1. _______________________________________________________ [1] (c) The flow rate of the liquid is affected by hydrogen bonding. (i) Explain what is meant by the term hydrogen bonding. ______________________________________________________ ____________________________________________________ [2] (ii) Draw a diagram showing the hydrogen bonding between two ethanol molecules. [1] (iii) Suggest why glycerol has a greater viscosity than glycol which, in turn, has a greater viscosity than ethanol. ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] ASC3S6 1814 9 [Turn over (d) A student suggested that the flow rate depended on the relative molecular mass (RMM) rather than hydrogen bonding, because the RMM of glycerol is greater than that of glycol or ethanol. Devise and explain an experiment that would demonstrate that RMM did not affect flow rate, but hydrogen bonding did have an effect. Examiner Only Marks Remark __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ _______________________________________________________ [3] (e) An experiment was carried out, as shown below, using water and a charged plastic rod; the stream of water is attracted to the rod. water charged rod The water was attracted to the charged rod because it has polar molecules. (i) Explain the term polar. ______________________________________________________ ____________________________________________________ [2] ASC3S6 1814 10 [Turn over (ii) Explain why the O H bond in water is polar. Examiner Only Marks Remark ______________________________________________________ ____________________________________________________ [1] (f) Draw diagrams to show a water molecule attracted to a positively charged rod and to a negatively charged rod. + [1] [1] ASC3S6 1814 11 [Turn over 4 Structured Examiner Only Marks Remark Limonene, an unsaturated hydrocarbon, is present in orange peel and may be obtained using the procedure described below. CH3 C CH2 CH CH2 CH2 CH C CH3 CH2 limonene The peel of three oranges and 75 cm3 of water are blended together and then placed in a flask and the apparatus arranged for distillation. heat The flask is heated and 30 cm3 of distillate are collected. Limonene forms as a small layer on top of the distillate. The distillate is transferred to a separating funnel and shaken with 20 cm3 of 1,1,1-trichloroethane. The 1,1,1-trichloroethane is run off into a beaker containing anhydrous sodium sulphate. The contents of the beaker are filtered and the 1,1,1-trichloroethane distilled off to leave limonene. ASC3S6 1814 12 [Turn over (a) Suggest two practical reasons why all the limonene present in the orange peel is not obtained. Examiner Only Marks Remark __________________________________________________________ _______________________________________________________ [2] (b) (i) Explain, giving practical detail, how you would use the separating funnel to separate the solution of limonene in 1,1,1-trichloroethane (density = 1.3 g cm 3) from water. ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] (ii) Draw the structure of 1,1,1-trichloroethane. [1] (iii) Explain why limonene dissolves in 1,1,1-trichloroethane and is insoluble in water. ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] (c) Explain the function of the anhydrous sodium sulphate. _______________________________________________________ [1] ASC3S6 1814 13 [Turn over (d) The peel of three oranges had a mass of 120 g. Determine the percentage by mass of limonene in the orange peel if 1.2 cm3 of limonene (density = 0.8 g cm 3) were obtained. Examiner Only Marks Remark __________________________________________________________ __________________________________________________________ _______________________________________________________ [3] (e) Bromine water may be used to show that limonene is unsaturated. (i) Explain the term unsaturated. ______________________________________________________ ____________________________________________________ [1] (ii) State two observations when bromine water is shaken with limonene. ______________________________________________________ ____________________________________________________ [2] (iii) Complete the following equation for the reaction of limonene with excess bromine. CH3 C CH2 CH CH2 CH2 + 2Br2 CH C CH3 CH2 ASC3S6 1814 [2] 14 [Turn over (f) Limonene, C10H16 burns with a sooty flame when it is ignited in air. Examiner Only Marks Remark (i) Write an equation for the complete combustion of limonene using its molecular formula. ____________________________________________________ [2] (ii) Name the products formed by the incomplete combustion of limonene which are not formed during complete combustion. ______________________________________________________ ____________________________________________________ [2] ASC3S6 1814 15 [Turn over S 12/05 4200 302507(124) [Turn over

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Additional Info : Gce Chemistry May 2006 Assessment Unit AS 3 Module 3: Practical Examination 1
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