DHS Prelim P3 Qn

This question paper consists of 11 printed pages and 1 blank page. © DHS 2015 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2015 Year 6 H2 CHEMISTRY 9647/03 Paper 3 Free Response 25 September 2015 2 hours Additional Materials: Data Booklet Writing Paper Cover Sheet INSTRUCTIONS TO CANDIDATES Write your name, register number and class on this question paper and on the Cover Sheet provided. 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 any four questions. Start each question on a fresh sheet of paper. 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 work securely together with the Cover Sheet on top.  Hand in the question paper separately. The total marks for this paper is 80 marks.

2 © DHS 2015 9647/03 [Turn over Answer any four questions on writing paper. 1 (a) Non–aqueous ionic liquids, or simply ionic liquids, generally have high boiling point and low melting point. They are becoming popular solvents in organic synthesis. Ionic liquids mainly consist of ions, and at least one of them is a bulky organic ion. 1–ethyl–3–methylimidazolium tetrafluoroborate, [emim]BF 4, is an example of ionic liquid. (i) Some ionic liquids, including [emim]BF 4, are liquid at room temperature. They are called ‘room temperature ionic liquids’. Account for the low melting point of [emim]BF4. (ii) Explain why [emim]BF4 has high boiling point. (iii) Suggest an advantage of using ionic liquids over using organic solvents such as acetaldehyde (CH3COCH3) in organic synthesis. Explain your answer. [4] The two most abundant atmospheric gases react to a small extent to achieve dynamic equilibrium as shown: N2 (g) + O2 (g) 2NO (g) Kp = 0.40 (b) Atmospheric oxygen and nitrogen, each at a partial pressure of 0.80 atm, are put into a 1 dm 3 evacuated flask and equilibrium is established after 30 minutes. Calculate the equilibrium partial pressure for each of the three components at 298 K. [3] (c) On the grid provided at the back of the Cover Sheet, sketch pressure versus time curves for N 2 and NO under the conditions described in (b) at 298K from 0 to 40 minutes. Label the axes, curves and indicate significant values on the axes. [2] (d) State how the pressure verses time curves for N 2 and NO from 0 to 40 minutes will be different from that in (c), when a catalyst is used in the reaction. [1] (e) The temperature of the system was raised to 350 K at 40 min. Given the average bond energy of N=O bond is 607 kJ mol –1 and that the equilibrium is re–established at 60 min, sketch on the same axes, the pressure versus time curves for N 2 and NO from 40 min to 70 min. [3]

3 © DHS 2015 9647/03 [Turn over (f) Halofenozide, K, is an insecticide commonly used for white grub control. It can be synthesised as shown below. One mole of H, J and K each reacts with alkaline aqueous iodine and forms a yellow precipitate in a ratio of 1: 1: 2. Compound J and K does not give any effervescence with anhydrous Na2CO3. Suggest the structures for J and K and give the reagents and conditions for step 1. [3] (g) LiAlH 4 is a powerful reducing agent that reacts with most polar functional groups. 0.02 mol of L reacts with sodium metal to give 0.48 dm 3 of gas at room temperature and pressure. L turns moist red litmus paper blue. formula p Kb L ? (CH3CH2)2NH 3.1 C6H5NH2 9.4 Using the information given above, predict the structure for product L and its p Kb value. Explain the chemistry of the reaction and property of L. [4] [Total: 20]

4 © DHS 2015 9647/03 [Turn over 2 One of the ingredients present in bread is calcium iodate( V), Ca( IO3)2. It is a dough conditioner added to bread dough to strengthen its texture. (a) Draw a dot–and–cross diagram for calcium iodate(V). [2] (b) At high temperatures, calcium iodate( V) undergo decomposition to form a white solid, a colourless gas and violet iodine vapour. (i) Construct an equation, with state symbols, to represent the above decomposition process. (ii) Use the Data Booklet , explain the difference in thermal stability of calcium iodate(V) and barium iodate(V). [4] (c) When the violet iodine vapour formed from the above decomposition process is bubbled into a closed vessel, containing a gaseous alkene, the violet vapour was decolourised and a liquid compound, with relative molecular mass of 310 was obtained. However, a colourless liquid cy clohexane turns violet when iodine vapour is bubbled into it. Given that this alkene exhibit geometric isomerism, deduce its identity and explain all the observations made. [4] (d) Consider the equilibrium dissolution of calcium iodate: Ca(IO3)2(s) Ca 2+(aq) + 2IO3 – (aq) (i) The standard enthalpy change, ∆H and the standard entropy change, ∆S for the process were +80 kJ mol –1 and + 152 J mol –1 K–1 respectively. G , in Joules per mole, and Ksp are related by the following equation G = –2.303 RT lg Ksp Calculate the value of the solubility product of calcium iodate( V) at 25 C, stating its units. (ii) The standard redox potential of iodate(V) ions is given below. 2IO3 – + 12H+ + 10e– I2 + 6H2O E = +1.20 V Use the Data Booklet, predict what you would expect to observe when acidified potassium iodate(V) is mixed with hydrogen peroxide. Calculate the E cell for the reaction and write a balanced equation. [6]

5 © DHS 2015 9647/03 [Turn over (e) Successive reactions of dihalgeno compounds are shown below. The following transformations show the different reactivities of organic halogeno compounds and of amines and alcohols. Suggest the structures of compounds C, D, E and F. (i) OH CH3 ACH3 I 1 mole of NaOH Cl C methylamine in ethanol D C7H15NO (ii) CH3CHICOCl ethane-1,2-diol E Na, warm F C5H8O3 [4] [Total: 20]

6 © DHS 2015 9647/03 [Turn over 3(a) By selecting appropriate E values from the Data Booklet, explain why iron( II) iodide can be crystallised from an aqueous mixture of iron( II) sulfate and potassium iodide, but iron( III) iodide cannot be produced by mixing any aqueous solutions of iron( III) and iodide ions. [3] (b) The solubility products, Ksp, of two silver salts at 25 C are given below. salt Ksp / mol2 dm6 AgSCN 1.03  10–12 AgI 8.52 x 10 –17 The solubility product for silver ethanoate, CH 3CO2Ag, was found by the following method. A saturated solution was first prepared by shaking 40 cm 3 of 0.20 mol dm –3 silver nitrate with 40 cm 3 of 0.20 mol dm –3 sodium ethanoate and maintained for some hours at a temperature of 25 C. A 20.0 cm 3 portion of this saturated solution was pipetted through a glass–wool filter and acidified with nitric acid to prevent the interference of other ions like carbonates with silver ions. A few drops of iron( III) solution was added as an indicator and the mixture was then titrated against 0.10 mol dm –3 potassium thiocyanate, KSCN. A red colouration signalled the end–point. (i) Write an equation, with state symbols, for the reaction that occurred during the titration. (ii) What causes the red colouration at end–point? (iii) Suggest why the red colouration only appears at end–point. (iv) Explain why the silver nitrate – sodium ethanoate mixture was initially kept at 25 C and suggest, with reason, whether the