MI H1 CHEM 8873 02

Class Adm No Candidate Name: This question paper consists of 17 printed pages and 1 blank page. 2018 End-of-Year Exams Pre-University 2 H1 CHEMISTRY 8873 / 02 Paper 2 Structured Questions 11 Sept 2018 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions. The use of an approved scientific calculator is expected, where appropriate. 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. Question 1 2 3 4 5 Section B Total Marks 15 10 15 9 11 20 80

2 Section A Answer all questions in the spaces provided. For Examiners’ Use 1 In acidic solution, bromate(V) ions, BrO3–, oxidises bromide ions to bromine. The progress of the reaction may be followed by adding a fixed amount of phenol (an aromatic alcohol) together with methyl red indicator. The bromine produced during the reaction reacts very rapidly with phenol. When all the phenol is consumed, any excess bromine bleaches the indicator immediately. The initial rate of formation of Br 2 is indicated by the time taken for the bromine to bleach the indicator. (a) An experiment was carried out four times at room temperature. The total volume of the reaction mixture is the same in all four experiments and the following data were obtained. Experiment [BrO3–] / mol dm–3 [Br –] / mol dm–3 Initial rate of formation of Br2 / mol dm–3 s–1 1 0.10 0.10 8 x 10 –2 2 0.10 0.05 4 x 10 –2 3 0.05 0.05 2 x 10 –2 4 0.05 0.10 4 x 10 –2 (i) Determine the order of the reaction with respect to each of the following reactants, showing your working clearly. I. BrO3– II. Br – [3] (ii) Based on your answer in (a)(i), sketch a concentration-time graph for BrO3 -. [1]

3 [Turn over (iii) Describe, and explain in molecular terms, how the rate of reaction is affected by an increase in temperature. You should make reference to the Boltzmann distribution in your answer. For Examiners’ Use ……………………………………………………………………………………………………... ........... ……………………………………………………………………………………………………... ........... ……………………………………………………………………………………………………... ........... ……………………………………………………………………………………………………... .......[3] (b) (i) State the oxidation number of the Br atom in each of the following substances: I. BrO3– Oxidation number of the Br atom: __________ II. bromide, Oxidation number of the Br atom: __________ III. bromine Oxidation number of the Br atom: __________ [3] (ii) In a separate experiment, 20.0 cm 3 of 0.0200 mol dm −3 BrO 3− was found to react completely with 80.0 cm3 of 0.0100 mol dm−3 hydroxylamine, NH2OH. BrO3− ions were reduced as shown in the ion-electron equation below. BrO3– + 6e– + 6H+ → Br− + 3H2O Given that the original oxidation number of N in NH 2OH was -1, calculate the final oxidation number of N. [4]

4 (iii) Based on your answer in (b)(ii), suggest a possible product for the oxidation of hydroxylamine. ...…………………………………………………………………………………………………... ........[1] For Examiners’ Use [Total: 15] 2 Magnesium and aluminium are elements in Period 3 of the Periodic Table. (a) State and explain two factors that lead to aluminium having a higher melting point than magnesium. ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... ...............[2] (b) MgO and Al2O3 have giant ionic lattice structures. Explain why the melting point of Al2O3 is lower than MgO. ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... ...............[2] (c) Explain the following observations when separate samples of MgO and A l2O3 were added to water. Write suitable equation(s) were appropriate. I. MgO dissolves slightly in water to give a weakly alkaline solution II. Al2O3 did not dissolve when added to water. ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... ...............[2]

5 [Turn over (d) Unlike MgCl2, AlCl3 has the tendency to dimerise to form Al2Cl6. Draw the ‘dot-and-cross’ diagram of Al2Cl6 and explain how the dimer was formed. For Examiners’ Use ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... .................... ……………………………………………………………………………………………………... ...............[3] (e) Using the axes below, sketch the graph to show the electrical conductivity of the Period 3 elements from Na to Cl. [1] [Total: 10]

6 3 The following abstract is taken from an article from the popular online site ‘Chemistry World’. Mazda Motor Corporation has unveiled a new generation of catalytic converters that uses 70% to 90% less of the precious metals to purify exhaust emissions. The converters rely on nanoparticles of the catalytic metal, each less than five nanometres across, studded onto the surface of tiny ceramic spheres. The Japanese firm claims this is the first time a catalyst material has been achieved that features single, nanosized precious metal particles embedded in fixed positions. Automotive catalysts use platinum, rhodium and palladium nanoparticles instead of other larger particles to speed up chemical reactions of pollu tants such as nitrogen oxide, carbon monoxide and hydrocarbons, to create non-toxic emissions. Unfortunately, using platinum and palladium nanoparticles can result in negative impacts on human health. Ongoing research suggests that emissions of platinum-group metals from catalytic converters along US highways might be a root cause of an alarming rise in allergies and asthma. Adapted from ‘‘Catalytic Converters Go Nano’ ~ Ned Stafford For Examiners’ Use (a) (i) By writing a chemical equation, illustrate how automotive catalyst convert pollutants into non-toxic emissions. ……………………………………………………………………………………………………... .......[1] (ii) S