RVHS H2 Chem 2013 Prelim P2 Soln

River Valley High School 9647/02/PRELIM/13 [Turn over Preliminary Examination 2013 RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/02 Paper 2 Structured Questions 24 September 2013 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, Centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the space provided. A Data Booklet is provided. Do NOT write anything on it. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. ____________________________________________________________________________ This document consists of 17 printed pages and 1 blank page. For Examiner’s Use Paper 2 Question Number 1 2 3 4 5 6 Total Marks 12 14 4 11 16 15 72 Paper 1 40 Paper 3 80 Total 192 1054

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River Valley High School 9647/02/PRELIM/13 [Turn over Preliminary Examination 2013 3 (d) Write the equation for the reaction at the anode and cathode. [1] Cathode: Cu2+(aq) + 2e  Cu(s) Anode: Cu(s)  Cu2+(aq) + 2e (e) The variable resistor can be used to vary the current that is passed through a closed circuit. Predict how does the amount of c opper deposited in a fixed duration (t) varies as current is increased from 0.00A until 1.00A. Display your prediction in the form of a sketch graph. [1] (f) Design a laboratory experiment to investigate your prediction in (e) and hence allow an experimental value for Faraday’s Constant to be obtained. The following apparatus and chemicals are available for used. Wires Switch Digital Ammeter ( 0.001A) Variable resistor Batteries Mass balance ( 0.001g) Pure copper strips Copper (II) sulfate solution (i) The percentage error for the mass weighed using the mass balance should not exceed 1%. Ca lculate the minimum duration of time, in minutes, for 0.400 A of current to be passed through the circuit. Considering the max percentage error of mass balance, minimum mass of copper deposited = 0.100g nCu = 0.100  63.5 = 0.00157 mol ne = nCu  2 = 0.00315 nCu/ mol current / A 0 1056

River Valley High School 9647/02/PRELIM/13 [Turn over Preliminary Examination 2013 4 Q = I t = ne F min 7 . 12 60  s70.400 965000.00315 t min (ii) Considering your answer in (f)(i) , write a detailed plan for your experiment. Your plan should contain the following  all essential experimental details  the precautions taken to ensure accuracy  outline of how the results would be used to verify your predicted graph in (e).  hence explain how the results can be used to determine a value for the Faraday constant. [6] Procedure + Precautions 1. Set up the apparatus as in (c). 2. Close the circuit and set th e current to ____A using the variable resistor. 3. Open the circuit and disconnect the iron box/Cu electrode. 4. Wash and dry the iron box/Cu electrode carefully. 5. Weigh and record the mass of iron box/Cu electrode. 6. Reconnect the iron box/ Cu electrode, closed the circuit and allows the current to flow for t minutes. 7. Open the circuit and disconnect the iron box/ Cu electrode. 8. Wash and dry the iron box/Cu electrode carefully 9. Weigh and record the mass of iron box/Cu electrode again. 10. Repeat the experiment 2 times by setting the current to 2 other reasonable current. Data and Results Exp t I /A X = Mass of Cu electrode at 0 min /g Y = Mass of Cu electrode at t min / g X–Y = Mass of Cu deposited / g nCu =(X-Y) 63.5 / mol 1 0.400 2 0.800 3 1.20 With these results, a graph of nCu against current may be plotted for verification. OR Calculate for each experiment at a fixed current, 1057

River Valley High School 9647/02/PRELIM/13 [Turn over Preliminary Examination 2013 5 Mass of Cu deposited = (Mass of Fe box at t min) - (Mass of Fe box at 0 min) nCu = Mass of Cu deposited  63.5 With these results, a graph of nCu against current may be plotted for verification. To determine a value for Faraday’s Constant: Q = I t60 = ne F = 2 x nCu F (t in min) Find the gradient of the graph of nCu against current. F t I ngradient Cu 2 60  gradient tF   2 60 [Total: 12] 2 Haze levels in Singapore hit a record high of PSI 401 on 21 June this year, as a consequence of widespread forest fires in Indonesia. Many hospitals and clinics reported a spike in the number of patients seeking medical attention for respiratory problems, such as asthma and rhinitis. To provide quick relief from asthma symptoms, the dr ug salbutamol is commonly prescribed. salbutamol (a) Identify two functional groups, other than phenyl, that are present in salbutamol. [1] Primary alcohol, secondary alcohol, phenol, secondary amine 1058

River Valley High School 9647/02/PRELIM/13 [Turn over Preliminary Examination 2013 6 (b) Salbutamol is sold in pharmacies as a racemic mixture, mainly because the ( S)-enantiomer blocks metabolism pathways while the (R)-enantiomer shows activity. Identify the type of ster eoisomerism salbutamol exhibits and draw two structures to illustrate this. [2] Optical isomerism A 4-step synthesis route of salbutamol is shown as follows: (c) An organic chemist suggested t he use of bromine gas under ultraviolet light in Step 2 . Explain why his choice of reagent and condition may not be appropriate for the conversion. [1] There is a possibility of many side products as random substitution of hydrogen atoms on any alkyl group found in the compound can occur. (d) Name the reaction in Step 3 and outline the mechanism. You may use R to denote bulky alkyl groups in your mechanism. [4] Nucleophilic substitution S