HCI H2 Chem 2013 Prelim P3 QP

This document consists of 11 printed pages and 1 blank page. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 12S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet 9647/03 20 September 2013 2 hours INSTRUCTIONS TO CANDIDATES Write your name and class on all the work you hand in. Write in dark blue or black pen. 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 any four questions. Begin each question on a new piece of paper. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. Write down the question numbers for the questions that you have attempted on the cover page provided. 646

2 © Hwa Chong Institution 2013 9647 / 03 / C2 Prelim 2013 Answer any four questions. 1 (a) Sodium chloride and sodium iodide react differently when warmed with concentrated sulfuric acid. Describe what you would observe when these reactio ns are carried out, write equations for the reactions that occur and suggest an explanation for these different reactions. Include state symbols in your equations. [5] Solvent extraction is an analytical technique which involves extracting a solute dissolved in one solvent with another solvent. The two solvents must be immiscible with each other. The ratio of the concentrations of the solute in the two solvents at equilibrium is a constant value called the partition coefficient. For this partition law to hold true, the solute must exist in the same molecular form in both solvents. (b) At room tem perature, an aqueous solution of iodine containing 1.20 × 10 −3 mol dm −3 of iodine was found to be in equilibrium with a solution in tetrachloromethane containing 0.102 mol dm−3 of iodine. Calculate the partition coefficient of iodine betwe en tetrachlor omethane and water, and comment on the significance of the value obtained. [2] (c) When iodine is dissolved in aqueous potassium iodide, it forms the triiodide complex ion according to the following equilibrium. I2(aq) + I−(aq) ⇌ I3 −(aq) reaction 1 To determine the equilibrium constant of the above reaction, a solution of iodine dissolved in 0.100 mol dm −3 aqueous potassium iodide was shaken with tetrachloromethane until equilibrium was reached at room temperature. The tetrach loromethane layer contained 0.0850 mol dm −3 of I2. The aqueous layer was found to contain I2 and I3 − at a total combined concentration of 0.0170 mol dm−3. (i) Use the value of the partition coefficient calculated in (b) to deter mine the concentration of I2 in the aqueous layer. (ii) Calculate the concentrations of I3 − and I− in the aqueous layer. (iii) Write an expressio n for Kc for reaction 1 and calculate its value. Indicate units in your answer. [6] 647

3 © Hwa Chong Institution 2013 9647 / 03 / C2 Prelim 2013 (d) Chlorine and iodine can form many interhalogen compounds. One such interhalogen compound is iodine monochloride, ICl. Iodine monochloride can be used to halogenate benzene. When this reaction is carried out in a suitable polar solvent, a Lewis acid catalyst is not required. (i) Suggest why a Lewis acid is not required in the reaction. (ii) Describe the reaction mechanism for the reaction between benzene and iodine monochloride. [4] (e) Iodine monochloride disproportionates when warmed with sodium hydroxide. (i) State, with a reason, which of the two halogen atoms in iodine monochloride undergoes disproportionation. (ii) Give an equation for the disproportionation of iodine monochloride in aqueous sodium hydroxide. [3] [Total: 20] 648

4 © Hwa Chong Institution 2013 9647 / 03 / C2 Prelim 2013 2 Carbonyl compounds react with HCN to form cyanohydrins via a nucleophilic addition reaction. (a) In an experiment to study this reaction, propanone, HCN and KCN were mixed in the following concentrations. Propanone : 0.100 mol dm–3 HCN : 0.010 mol dm–3 KCN : 0.010 mol dm–3 The concentration of HCN was monitored as the reaction proceeds. (i) Based on your knowledge of the mechanism for the reaction, sketch the graph of [HCN] vs time that you would expect to obtain. (ii) In the experiment, the half-life of propanone was 20.0 s. Predict and explain the half -life of propanone if the concentration of KCN used was 0.020 mol dm–3 instead. [2] (b) The reaction between propanone and HCN is an important step used to synt hesise the monomer methyl methacrylate, in the production of acrylic glass. methyl methacrylate (i) Draw the displayed formula of the product obtained when propanone reacts with HCN under suitable conditions. (ii) Starting with the product in b(i), outline a three -step reaction scheme to obtain methyl methacrylate. Your answer should include clearly the reagents and conditions in each step, and the structures of all intermediates formed. [4] (c) For each of the three compounds given below, suggest a simple chemical test that will identify it from the other two via a positive result. For each test, give reagents and conditions and state the observations for each of A, B and C. Your test(s) may rely o n a preliminary breaking-up of the compound, and subsequent testing of the reaction products. [6] 649

5 © Hwa Chong Institution 2013 9647 / 03 / C2 Prelim 2013 (d) One mole of hydrocarbon R (Mr = 136), reacts with three moles of hydrogen gas in the presence of nickel catalyst. Pro longed oxidation of R yields carbon dioxide, S (C4H6O3) and T (C3H6O) in mole ratio 3:1:1. Both S and T react with alkaline aqueous iodine to give a pale yellow precipitate . Compound U can be synthesized by reacting S with thionyl chloride (SOCl2), followed by ethylamine. (i) Determine the molecular formula of R. (ii) Deduce the structures of compounds R, S, T and U, and explain the reactions described. Equations are not required. [8] [Total: 20] 650

6 © Hwa Chong Institution 2013 9647 / 03 / C2 Prelim 2013 3 In 2009, archaeologists discovered a well -preserved vial of perfume in the tom b of Queen Hatshepsut, a female pharaoh who ruled the Ancient Egypt. The 2.0 g of fluid in the vial contained plant extracts like methyl butanoate, which made up 18.4 % by mass . Some ethanol and water were also present. (a) The human nose can detect the strawberry smell of methyl butanoate at a minimum concentration of 10 ppm (parts per million) by mass. Assuming that all the fluid found in the vial was extracted and vapourised, calculate the volume of a room above which the smell of methyl butanoate can no longer be detected by the human nose. Assume density of the air in the room is 1.20 kg m–3. [1 ppm by mass is 1 g in 1 x 106 g] [2] Ancient Egyptian perfumes uncovere d by archaeologists had seldom retain ed their aromas. Instead the aromas were often repla