DHS Prelim P3 Qn

This question paper consists of 14 printed pages and 0 blank page. © DHS 2017 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2017 Year 6 H2 CHEMISTRY 9729/03 Paper 3 Section A and B (Free Response) 18 September 2017 2 hours Additional Materials: Data Booklet Writing Paper Cover Sheet INSTRUCTIONS TO CANDIDATES 1 Write your name, index number and class on this cover page and on the Cover Sheet provided. 2 Write your answers on the separate writing papers provided. 3 Write in dark blue or black pen. 4 You may use an HB pencil for any diagrams or graphs. 5 Start each question on a fresh sheet of paper. 6 At the end of the examination:  Fasten all your work securely together with the Cover Sheet on top. 7 Do not use staples, paper clips, glue or correction fluid. Section A 8 Answer all questions in this section. Section B 9 Answer one question from this section. The number of marks is given in brackets [ ] at the end of each question or part question. You are advised to show all workings in calculations. You are reminded of the need for good English and clear presentation in your answers.

2 © DHS 2017 9729/03 [Turn Over Section A Answer all questions. 1 (a) Singapore has been affected by severe smoke haze due to forest fires in the region periodically. The National Environment Agency (NEA) is taking action to ensure that its population is better equipped to deal with haze. During one of the sample analys is of air, the air sample was found to contain elevated amounts of NO2 and gas S. By careful measurement s and extrapolation, the value of 𝑝 ρ for gas S has been found to be approximately 110.3, at 100 °C and at very low pressure. [𝑝 is the pressure of the gas in Pa and ρ is the density of the gas in g m–3] 𝑝 (i) State two main assumptions of the kinetic theory, and use these to explain why you might expect the behaviour of nitrogen dioxide to be less ideal compared to that of hydrogen. [3] (ii) Calculate an approximate value for the relative molecular mass of S. [1] (iii) Hence, identify gas S, where S is a diatomic neutral pollutant. [1] (b) Atmospheric sulfur dioxide is a major air pollutant that forms acid rain. The pollution problem caused by sulfur dioxide is amplified in the presence of atmospheric oxides of nitrogen, which act as a homogeneous catalyst. Explain, with the aid of equation(s), how atmospheric oxides of nitrogen act as a homogeneous catalyst to amplify the pollution problems of sulfur dioxide. [3] 110.3 𝑝 ρ

3 © DHS 2017 9729/03 [Turn Over (c) The Contact Process is an important industrial process that occurs at 450 °C. The key stage in this process is the reaction between sulfur dioxide and oxygen. 2SO2(g) + O2(g)  2SO3(g) Two laboratory experiments were conducted at 450 °C to investigate the kinetics of this reaction. The graph below shows the results obtained when concentrations of sulfur dioxide were varied. [O2] / mol dm–3 (i) Use the graph s above to deduce the order of reaction with respect to sulfur dioxide and oxygen. [3] (ii) Using one of the graphs above, calculate the value of rate constant, stating its units. [2] (iii) Using your answer in (i), sketch the graph of concentration of sulfur dioxide against time for this reaction, while keeping [O 2] constant. Use construction lines to label the first and second half-lives in your sketch. [1] (iv) Sketch and label clearly, on the same axes as in (iii), how the graph would look like if the experiment was conducted at 200 °C. [1] [Total: 15] 0 0.01 0.02 0.03 0.04 0.05 0.06 0 20 40 60 80 100 120 140 160 Time / s Expt 1 [SO2] = 0.8 mol dm-3 Expt 2 [SO2] = 1.2 mol dm-3

4 © DHS 2017 9729/03 [Turn Over 2 (a) Two 1.0 mol samples of hexane are mixed with separate 1.0 mol samples of cyclohexane and ethanol. The following results were obtained. hexane mixed with observations cyclohexane no heat is absorbed or given out ethanol 1.0 kJ of heat is absorbed For each mixture, consider interactions between molecules of the two liquids mixed and explain the observations. [4] (b) In the presence of peroxides, H X may be added to alkenes by a free radical mechanism. The addition is said to be anti-Markovnikov, that is, the H atom from HX attaches itself to the C atom in the carbon -carbon double bond with the least number of H atoms. The propagation steps for propene are as follows. step 1 CH3CH=CH2 + X CH3CHCH2X step 2 HX CH3CH2CH2X+ + XCH3CHCH2X The table below shows values of the enthalpy changes, H, for the propagation steps 1, 2, and for the overall reaction for HX respectively. X Cl Br I Hstep 1 / kJ mol–1 –80 –20 +20 Hstep 2 / kJ mol–1 +21 –44 –111 Hoverall / kJ mol–1 –59 –64 –91 (i) By selecting relevant data from the Data Booklet, show that Hstep 1 for H I and Hstep 2 for HCl are +20 kJ mol–1 and +21 kJ mol–1 respectively. [2] (ii) Experiments show that only HBr adds across an alkene via free radical mechanism. With reference to the H values given above, explain why HBr is most likely to do so and why the other two HX does not undergo the same mechanism. [2] (iii) Hence suggest the structure of the major product formed when H I that is contaminated with small amount of peroxides is added to propene. [1]

5 © DHS 2017 9729/03 [Turn Over (c) The following scheme shows the reactions of P, a dihalogen derivative of 1,2-dimethylcyclohexane. Cl CH3 CH3 I precipitate Q forms immediately + precipitate R forms after several minutes P Cl CH3 CH3 S Cl CH3 CH3 T CH3 OH O CH3 Cl O warm ethanolic AgNO3 I II H2SO4(aq) III OH OH O CH3 OH O IV (i) Identify precipitates Q and R. With reference to the type of reaction that P has undergone in reaction I, explain the sequence in which Q and R are formed. Support your answer with suitable data from the Data Booklet. [3] (ii) LiAlH4 is a powerful reducing agent commonly used in organic chemistry to reduce carbonyl compounds, carboxylic acids and their derivatives. However when LiAlH4 is used to reduce S in reaction II, T is not formed. Explain these observations. [2] (iii) State the reagents and conditions required for reaction III. [1] [Total: 15]

6 © DHS 2017 9729/03 [Turn Over 3 The chemistry of Group 15 elements, also known as Pnictogens, is discussed in this que