JJC H2 Chem 2013 Prelim P2 QP

[Turn over JURONG JUNIOR COLLEGE 2013 JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS EXAM INDEX NUMBER CHEMISTRY 9647/02 Paper 2 Structured Questions 30 August 2013 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and exam 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. A Data Booklet is provided. 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. For Examiner’s Use 1 2 3 4 5 6 7 Total This document consists of 18 printed pages and 2 blank pages. 596

2 © Jurong Junior College 9647/02/PRELIM/2013 1 Planning (P) For Examiner’s Use Solubility of a substance is the maximum mass of the substance dissolved in a given volume of a particular solvent to give a saturated solution at a specified temperature. The units of solubility is grams per hundred grams of water (i.e. g /100 g water). When solid potassium nitrate is dissolved in water, the temperature of solution decreases. KNO3(s)  K+(aq) + NO3 –(aq) To investigate how the solubility of potassium nitrate varies with temperature, a student demonstrated the experiment, at 30 °C, as follows. The solid was added into 50 cm 3 of water in a small beaker until a saturated solution at 30 °C is obtained. The mixture was filtered and the filtrate was collected in a crucible. The filtrate in the crucible was heated to evaporate off the water and the mass of potassium nitrate dissolved in 50 cm 3 of water was determined. (a) Predict, in the form of a sketch graph, how the solubility of potassium nitrate changes if the solution temperature is increased. Explain your answer. Explanation: ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. [2] (b) State and explain one limitation for heating the solid to dryness. …………………………………………………………………………………...…………. ……………………………………………………………………………………...………. [1] 597

3 © Jurong Junior College 9647/02/PRELIM/2013 [Turn over 1 (c) Consider the brief description of the experiment given on Page 2. The prediction in (a) can be determined by performing a number of experiments. Write a plan for such a series of experiments. In your plan, you should use the same volume of water to dissolve the solid as described on Page 2. Your plan should also ensure that the temperature of each solution is between 30 °C and 70 °C. You may assume that you are provided with the following:  a bottle of pure anhydrous solid potassium nitrate,  thermometer covering the temperature range of 0 °C to 100 °C,  thermostat to maintain the temperature of water–bath,  crucible,  deionised water and  apparatus normally found in a school or college laboratory. Your plan should include the following:  the choice of number of experiments to conduct to ensure a wide range of results suitable for analysis;  the choice of temperature for each experiment;  all essential experimental details including the apparatus used and measurements recorded. For Examiner’s Use Experimental procedure: ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. 598

4 © Jurong Junior College 9647/02/PRELIM/2013 1 (c) ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. ……………………………………………………………………………………...………. [7] For Examiner’s Use 599

5 © Jurong Junior College 9647/02/PRELIM/2013 [Turn over 1 (d) The following data was collected for the experiment conducted at 30 °C. mass of crucible /g x mass of crucible with solid residue /g y Outline how you would calculate the solubility of potassium nitrate, at 30 °C, given that the density of water is 1 g cm–3. For Examiner’s Use [1] (e) State one safety precaution which must be taken in this experiment. …………………………………………………………………………………...…………. ……………………………………………………………………………………...………. [1] [Total: 12] 600

6 © Jurong Junior College 9647/02/PRELIM/2013 2 The equation for the reaction of iodine with propanone in the presence of H + is shown below. CH3COCH3 + I2 CH3COCH2I + HI The following experiment is carried out as part of an investigation into the mechanism of the iodination of propanone which is catalysed by H+. Experimental procedure: 1. 50 cm 3 of iodine solution was added to 25 cm3 of sulfuric acid in a conical flask. 2. 25 cm 3 of propanone solution was added to the mixture and a timer started. 3. A 10 cm 3 of sample was drawn out from the conical flask after one minute and added immediately to 20 cm3 of sodium hydrogen carbonate solution in a conical flask. 4. The resulting mixture from step 3 was then titrated with a standard solution of sodium thiosulfate, Na2S2O3. 5. Steps 3 to 4 were repeated for subsequent 10 cm 3 samples withdrawn at three minute intervals. For Examiner’s Use (a) (i) Explain why each sample was added to sodium hydrogen carbonate solution in step 3. …………………………………………………………………………………....... ……………………………………………………………………………………... ……………………………………………………………………………………... (ii) Write an ionic equation for the reaction occurring in step 4 of the experimental procedure. …………………………………………………………………………………....... (iii) To determine the order of reaction with respect to iodine, propanone is used in large excess. Explain why it is not necessary to use sulfuric acid in large excess. …………………………………………………………………………………....... ……………………………………………………………………………………... ……………………………………………………………………………………... [3] H+ 601

7 © Jurong Junior College 9647/02/PRELIM/2013 [Turn over 2 (b) The following results were obtained in the experiment. Time/ min Volume of sodium thiosulfate solution used / cm3 1 19.0 4 16.0