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GCE MAY 2008 : (AS 3) Practical Examination 2

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Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education 2008 Chemistry assessing Module 3: Practical Examination 2 ASC32 Assessment Unit AS 3 [ASC32] FRIDAY 16 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 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 ASC3aS8 3698 Marks 1 Observation/deduction Safety goggles must be worn at all times during this practical examination. Care should be exercised, especially when using sodium hydroxide solution and concentrated hydrochloric acid. (a) You are provided with 2 g of a mixture, labelled X, which contains two salts with a common anion but different cations. Carry out the following experiments on the mixture. Record your observations and deductions in the spaces below and identify the two salts in X. Experiment 1 Observations Deductions Describe the appearance of X. 2 (a) Add half a spatula-measure of X to a test tube halffull of sodium hydroxide solution and warm gently. (b) Test the gas evolved with damp Universal Indicator paper. (c) Test the gas evolved by dipping a glass rod into concentrated hydrochloric acid and holding it over the mouth of the test tube. 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA 3 Dip a nichrome wire loop into concentrated hydrochloric acid; touch sample X with the wire, then hold it in a blue Bunsen flame. 4 Dissolve half a spatulameasure of X in about 2 cm3 of dilute nitric acid. Add 2 cm3 of silver nitrate solution. Name the two salts present in X ______________________________________________ Name the two salts in X ASC3aS8 3698 ______________________________________________ 2 [Turn over (b) You are provided with an organic liquid labelled Y which has the formula C3H8O. Carry out the following experiments. Record your observations and deductions in the spaces below. Suggest a structure for Y. On completion of your experiments, dispose of Y in the container provided. Experiment Observations Describe the liquid Y. 2 Add 2 cm3 of Y to 2 cm3 of water. 3 Place 5 drops of Y on a watch glass placed on a heatproof mat and ignite using a splint. 4 Add 1 cm3 of dilute sulphuric acid to 2 cm3 of potassium dichromate solution. Add 10 drops of Y and warm gently. 5 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA 1 Deductions Add 1cm3 of a solution of iodine in potassium iodide. Add 10 drops of Y followed by 1 cm3 of sodium hydroxide solution. Add 1 cm3 of sodium hypochlorite solution. Functional group in Y ______________________________________________________ Class of compounds ______________________________________________________ Structure of Y ___________________________________________________[25] ASC3aS8 3698 3 [Turn over 2 Titration (a) You are provided with: Sulphuric acid of unknown concentration, but approximately 0.5 mol dm 3, sodium hydroxide solution of concentration 0.1 mol dm 3, methyl orange indicator. You are required to: (i) dilute the sulphuric acid using a pipette and a volumetric flask. (ii) titrate the sodium hydroxide solution against the diluted sulphuric acid using methyl orange as indicator. Procedure (i) Dilution dilute sulphuric acid Using the pipette and pipette filler, place 25.0 cm3 of the sulphuric acid in a 250 cm3 volumetric flask. Add deionised water to the flask, inverting the flask as the level approaches the mark. Fill to the mark with deionised water. Stopper and mix well by inversion. (ii) Titration 0.1mol dm 3 sodium hydroxide solution 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA diluted sulphuric acid and methyl orange ASC3aS8 3698 Rinse out the burette with the 0.1 mol dm 3 sodium hydroxide solution. Fill the burette with 0.1 mol dm 3 sodium hydroxide solution. Rinse out the pipette with diluted sulphuric acid solution. Using the pipette and a pipette filler, place 25.0 cm 3 of the diluted sulphuric acid solution in the conical flask. Add 2 or 3 drops of the methyl orange to the conical flask and titrate with the 0.1 mol dm 3 sodium hydroxide 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 at the end point. From __________________ to __________________ [1] (c) (i) Write an equation for the reaction of sulphuric acid with sodium hydroxide. ___________________________________________________ [2] (ii) Using the average titre, calculate the number of moles of sodium hydroxide used. ___________________________________________________ [1] 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA (iii) Use the ratio in which sulphuric acid reacts with sodium hydroxide to calculate the number of moles of sulphuric acid present in 25.0 cm3 of diluted solution. _____________________________________________________ ___________________________________________________ [2] ASC3aS8 3698 5 [Turn over (iv) Calculate the number of moles of sulphuric acid present in the 250 cm3 volumetric flask. Examiner Only Marks Remark _____________________________________________________ ___________________________________________________ [2] (v) Calculate the concentration, in mol dm 3, of the undiluted sulphuric acid. ___________________________________________________ [1] (vi) Calculate the concentration, in g dm 3, of the undiluted sulphuric acid. 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA ___________________________________________________[1] ASC3aS8 3698 6 [Turn over BLANK PAGE 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA (Questions continue overleaf) ASC3aS8 3698 7 [Turn over 3 Planning Examiner Only Marks Remark You are required to plan an experiment to find the enthalpy of combustion of a series of simple hydrocarbons using a basic calorimeter. The apparatus below could be used to carry out the experiment. thermometer water C A decane (a) (i) State the purpose of the piece of apparatus labelled A. ___________________________________________________ [1] (ii) State and explain the purpose of C. _____________________________________________________ ___________________________________________________ [2] (b) The following results were obtained for the combustion of decane, C10H22: 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA Initial mass of decane Final mass of decane Initial temperature Final temperature Mass of water = 19.8 g = 19.6 g = 22 C = 28 C = 0.15 kg (i) What mass of decane was burned? ___________________________________________________ [1] (ii) How many moles of decane were burned? ___________________________________________________ [1] (iii) What was the temperature rise during the experiment? ___________________________________________________ [1] ASC3aS8 3698 8 [Turn over (iv) Calculate the molar enthalpy of combustion of decane. Heat received by water = mass of water temperature rise specific heat capacity of water. Specific heat capacity of water = 4.18 103 J kg 1 K 1 at 293 K. Examiner Only Marks Remark ______________________________________________________ ______________________________________________________ ____________________________________________________ [3] (v) Explain why the theoretical value for the combustion of decane is different from the experimental value. ___________________________________________________ [1] (c) (i) Write the equation for the complete combustion of decane. ___________________________________________________ [2] (ii) Name the gas produced, apart from water vapour, in the complete combustion of decane. ___________________________________________________ [1] (iii) How would you confirm the identity of this gas using a chemical test? State what would be observed. _____________________________________________________ ___________________________________________________ [2] 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA (iv) Calculate the mass of this gas produced when 1 tonne (106 g) of decane is burnt. _____________________________________________________ ___________________________________________________ [3] ASC3aS8 3698 9 [Turn over (d) When decane burns in a limited supply of air, carbon is formed. Write an equation for the incomplete combustion of decane, in which carbon is one of the products. Examiner Only Marks Remark 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA ______________________________________________________ [2] ASC3aS8 3698 10 [Turn over BLANK PAGE 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA (Questions continue overleaf) ASC3aS8 3698 11 [Turn over 4 Structured Examiner Only Marks Remark The following method can be used to prepare 1-bromopropane: CH3CH2CH2OH + HBr CH3CH2CH2Br + H2O Mr = 60 Mr = 123 Place 3 cm3 of propan-1-ol (density = 0.8 g cm 3) in a 25 cm3 flask. Weigh out 4.0 g of sodium bromide and add it and 4.5 cm3 of water to the propan-1-ol. Add 3.5 cm3 of concentrated sulphuric acid to form hydrobromic acid in situ. Add boiling chips, attach a condenser to the flask, and reflux the mixture for 45 minutes. Replace the condenser with a distillation setup, and distil the 1-bromopropane and water at a temperature below 80 C into a 10 cm3 flask, cooled in an ice-water bath. Add about 1 g of anhydrous sodium sulphate to the distillate, and swirl the mixture. Transfer the 1-bromopropane to a test tube and add 1.5 cm3 of conc. sulphuric acid. Mix the two layers thoroughly. Place the test tube in an ice-water bath and allow the layers to separate. Draw off the sulphuric acid and discard it into a beaker half-filled with ice. Add about 0.5 g of sodium sulphate to the 1-bromopropane, and after several minutes add 0.5 g of potassium carbonate, and mix well. Transfer the 1-bromopropane to a 10 cm3 flask. Set up the distillation apparatus as before and distil. Determine the mass of product. (a) (i) Write an equation to show how the hydrobromic acid is formed. ___________________________________________________ [2] (ii) Suggest the meaning of the term in situ. ___________________________________________________ [1] (b) Why are boiling chips added? _______________________________________________________ [1] 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA (c) (i) Draw a labelled diagram of the apparatus used to reflux the mixture. [3] ASC3aS8 3698 12 [Turn over (ii) State three changes made to the apparatus in order to set it up for distillation. Examiner Only Marks Remark _____________________________________________________ _____________________________________________________ ___________________________________________________ [3] (d) What is the function of the sodium sulphate? _______________________________________________________ [1] (e) Why should the receiver flask be clean and dry? _______________________________________________________ [2] (f) A student following these instructions obtained 4.0 g of 1-bromopropane. (i) Calculate the number of moles of propan-1-ol used. ___________________________________________________ [2] (ii) Calculate the number of moles of 1-bromopropane formed. ___________________________________________________ [1] (iii) Assuming that the hydrobromic acid was in excess, calculate the percentage yield of the 1-bromopropane. _____________________________________________________ 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA _____________________________________________________ ___________________________________________________ [1] ASC3aS8 3698 13 [Turn over Examiner Only (g) Referring to practical and theoretical considerations, suggest why the percentage yield is not 100%. Marks Remark Practical _________________________________________________ _________________________________________________________ Theoretical _______________________________________________ _______________________________________________________ [3] 1 12.01.07/ES 2 9.02.07/RTS 3 2.03.07/EA THIS IS THE END OF THE QUESTION PAPER ASC3aS8 3698 14 [Turn over S 7/07 528-006-1 [Turn over

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Additional Info : Gce Chemistry May 2008 Assessment Unit AS 3 Module 3: Practical Examination 2
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