MI H2 Chem 2012 Prelim P3 QP

Class Adm No Candidate Name: 2012 Preliminary Examination II Pre-university 3 H2 CHEMISTRY 9647/03 Paper 3 14 Sept 2012 2 hours Additional Materials: Writing Paper Data Booklet Graph Paper READ THESE INSTRUCTIONS FIRST 1. Do not turn over this question paper until you are told to do so. 2. Write your name, class and index number in the spaces provided at the top of this page and on all the work you hand in. 3. Write in dark blue or black pen on both sides of the paper. 4. You may use a soft pencil for any diagrams or graphs. 5. DO NOT use staples, paper clips, highlighters, glue or correction fluid or tape. 6. Answer any four questions. 7. Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place in the case of Mr and Ar, unless a different level of accuracy is specified in the question. 8. The number of marks is given in brackets [ ] at the end of each question or part question. 9. You are reminded of the need for good English and clear presentation in your answers and to show all working in calculations. 10. The use of a calculator is expected, where appropriate. This question paper consists of 7 printed pages. [Turn over

- 2 - Answer ANY FOUR quest ions 1 (a) When studying Hydrocarbons, we recognised the environmental consequences of carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the internal combustion engine. Because of these environmental concerns, alongside with high oil prices and oil being a limited natural resource, development of cleaner alternative fuels and advanced power systems for vehicles has become a high priority for many governments and vehicle manufacturers around the world. An alternative fuel vehicle is a vehicle that runs on a fuel other than "traditional" petroleum fuels (petrol or diesel); and also refers to any technology of powering an engine that does not involve solely petroleum (e.g. electric car, hybrid electric vehicles, solar powered). One such source of alternative fuel is the hydrogen / oxygen fuel cell , which is increasingly used in space crafts. Describe, providing details, the hydrogen / oxygen fuel cell. Include the following in your answer: · Draw a well-labeled diagram for the cell. · Outline the reactions taking place at each electrode, assuming an alkaline medium. · State one advantage of using this fuel cell. [6] (b) C yanogen is a highly toxic gas, composing of 46.2% carbon and 53.8% nitrogen by mass. At 25 ºC and 1 atm, 1.05 g of cyanogen occupies 0.500 dm3. (i) Determine the molecular formula of cyanogen. (ii) Draw the dot-and-cross diagram for cyanogen. Hence, state its shape. (iii) ‘Cyanogen is soluble in ethanol.’ Explain this statement with the aid of a suitable diagram. [7] (c) S ketch and explain the trend observed for the atomic and ionic radii of the elements (from Na to Cl) in Period 3. [4] (d) P hosphine, PH3, a gas at room temperature can be prepared by action of sodium hydroxide on phosphonium iodide, PH 4I. When 1.00 g of phosphonium iodide reacted with solid sodium hydroxide, 0.925 g of white solid was formed, together with steam and 150 cm 3 of PH3 gas. All measurements were taken at room temperature and pressure. Identify the white solid and use the information given to write a balanced equation with state symbols, for the preparation of PH3. [3] [Total: 20 marks]

- 3 - 2 (a) Halogen derivatives can be used to synthesize alcohols. The overall reaction is shown below: CH3CH2Br + NaOH → CH3CH2OH + NaBr State the type of reaction mechanism for the above reaction and illustrate how the reaction proceeds via the mechanism you stated. [3] (b) Describe the reactions of chloride, bromide and iodide ions with the f ollowing reagents: I. Aqueous silver nitrate, followed by aqueous ammonia II. Concentrated sulfuric acid You are required to write equations where appropriate and give explanations for the differences in their reactions. [7] (c) When a primary aromatic amine is treated with nitrous acid in a cool solution, the product is unstable compound, known as a diazonium salt. E rror! Objects cannot be created from editing field codes. Error! Objects cannot be created from editing field codes. One reaction the diazonium cation undergoes is the substitution of halides. The reaction is shown below, where X r epresents the halogen. C6H5N2+ + KX → C6H5X + K+ + N2 diazonium ion Compound P can be synthesised from benzoic acid in the reaction shown below. Suggest a synthetic route for the conversion of benzoic acid to compound P. In each case, identify all the intermediate compounds and state clearly the reagents and conditions used for each transformation. [*Note: In your proposed synthesis route, two of the stages of the synthesis requires the formation of the diazonium ion and the substitution of the halide.] [5 ] (d) Arrange the following halogen containing compounds according to increasing pKa values. Explain your answer. CH3CHClCOOH , CH3CCl2COOH , CH3CHBrCOOH [3] + HNO2 + HCl → diazonium salt 5 ºC + H2O

- 4 - (e) Explain the following physical property trends of transition metals across the Period. I: relatively constant atomic radius II: very high melting point [2] [Total: 20 marks]

- 5 - 3 (a) An Ellingham diagram shows how the change in Gibbs free energy for a particular reaction varies with temperature. The following shows a sketch of an Ellingham diagram for three reactions: I: 2C (s) + O2 (g) → 2CO (g) ∆G = (-223 – 0.18T) kJ mol-1 II: 2Fe (s) + O2 (g) → 2FeO (s) ∆G = (-525 + 0.13T) kJ mol-1 III: Al (s) + O2 (g) → Al2O3 (s) ∆G = (-1116 + 0.21T) kJ mol-1 (i) Predict and explain what will happen to the value of ∆G when the pressure of the system in reaction I is reduced. (ii) Explain why the gradient for reaction I is negative (downward sloping), while the gradient for reactions II and III are positive (upward sloping)? (iii) Calculate ∆G of the following reaction at 1000K: FeO (s)+ C (s) → Fe (s) + CO (g) (iv) Hence, what is the minimum temperature at which the reduction of iron (II) oxide by carbon becomes thermodynamically feasible? (v) Aluminium oxide a nd carbon have high melting points. With reference to the Ellingham diagram, explain why carbon is not used to line vessels that are used to contain molten steel saturated with oxygen. [The melting point of steel is 1800 K] [14] (b) The manipulation and rearrangement of the Gibbs free energy equation shows a relation between the change in Gibbs free energy and the standard electrode potential of a cell. (i) Define the term standard electrode potential of a cell. (ii) With the use of relevant data from the data booklet, state and illustrate how the relative stabilities of the Fe (II) / Fe (III) oxidation states are affected by the following changes: I. CN- ligands II. pH [6] [Total: 20 marks]

- 6 - 4 (a) Compound K is formed when phenylhydroxylamine, C6H5NHOH, is warmed with dilute sulfuric acid. Compound K has the following properties: · K is not very soluble in water, but dissolves in HCl (aq) · K dissolves in NaOH (aq) but not in Na2CO3 (aq) · K reacts with 1 mol of ethanoyl chloride to give compound L, C8H9O2N, which is not soluble in HCl (aq), but is soluble in NaOH (aq). · L reacts with Br2 (aq) to give compound M, C8H7O2NBr2. · K reacts with 2 mol of ethanoyl chloride to give compound N, C10H11O3N, which is not soluble in HCl (aq) or NaOH (aq). (i) Suggest structures for compounds K, L, M and N. Present your reasoning clearly by explaining the Chemistry involved. (ii) Write balanced chemical equations for each of the bullet points above to show how the reactions proceeded. [12] (b) A student was given 4 unlabelled bottles and each bottle contains one of the following organic com