JJC H2 CHEM P3

JURONG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS CHEMISTRY 9746/03 Paper 3 Free Response 21 August 2009 2 hours Candidates answer Section A on the Question Paper Additional Materials: Answer Paper Data Booklet Graph Paper READ THESE INSTRUCTIONS FIRST Write your name and class 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 any four questions. Begin your answer to each new question on a fresh sheet of writing paper. At the end of the examination, arrange the answers in numerical order and attach the cover sheet on top. A Data Booklet is provided. Do not write anything on the Data Booklet. 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 your work securely together. For Examiner’s Use Section A 1 2 3 4 Section B Answer all questions on separate answer paper. 5 This document consists of 10 printed pages and 2 blank pages. [Turn over

Answer any four questions. 1. Phenol is a powerful disinfectant and has antiseptic properties. Hence it is found in medicinal products such as ear and nose drops, throat lozenges and mouthwashes. (a) The standard enthalpy change of combustion of solid phenol is –3054 kJ mol -1. (i) What is meant by the term standard enthalpy change of combustion? (ii) Write the equation, with state symbols, which represents the standard enthalpy change of combustion of phenol. (iii) Using the following standard enthalpy changes of formation together with data given above, calculate the standard enthalpy change of formation of phenol. H f (CO2) = –394 kJ mol-1 Hf (H2O) = –286 kJ mol-1 (iv) Given that the standard entropy change for the formation of phenol is –384 J K-1mol-1, calculate the value of the standard free energy change, G, for the formation of phenol. [5] (b) 2,4,6-trichlorophenol is a chlorinated phenol which is a stronger germicide than phenol. 2,4,6-trichlorophenol (i) Predict and explain if 2,4,6-trichlorophenol has a larger or smaller K a value as compared to phenol. (ii) Suggest a suitable chemical test to distinguish between 2,4,6-trichlorophenol and phenol. [4] Cl Cl OH Cl Page 2 of 10

1. (c) 1-naphthol, a derivative of phenol, can be used to synthesize compound Q by the following reaction scheme. P 1-naphthol Compound Q (i) Suggest a suitable structure for the intermediate, P. (ii) State the reagents and conditions for Steps I and II. (iii) 1-naphthol is less soluble in water than phenol. Explain why. [4] (d) An alkaline solution of compound Q from part (c) can also act as a bidentate ligand. When the alkaline solution containing Q is added to a blue solution of Cu 2+ (aq), a pale blue precipitate R is formed. Analysis of R shows that the formula is Cu(C10H8NO)2(H2O)2. (i) Explain why the Cu2+ (aq) solution is coloured. (ii) Suggest a reason why Cu2+ has a tendency to form complexes. (iii) Draw the structural formula of R , showing the arrangement of the ligands in the structure. (iv) When excess of concentrated aqueous ammonia is added to R, the precipitate dissolves to form a deep blue solution. Identify the species that gives rise to the deep blue solution. [7] [Total marks: 20] OH OH NH2 Step II Step I Page 3 of 10

2. An active ingredient in aspirin is a weak monobasic acid called acetylsalicylic acid. Its molecular formula is C8H7O2CO2H. (Ka = 3.2 x 10–4 mol dm–3) 50 cm3 of 0.1 mol dm–3 acetylsalicylic acid was titrated against 0.1 mol dm –3 sodium hydroxide solution to obtain a titration curve as shown below: A (a) (i) Define the term “weak acid”. (ii) Calculate the pH of the solution in the conical flask at point A. (iii) Determine the volume of NaOH required for complete neutralisation, x, and hence calculate the pH of the solution at point B. [6] (b) At point C, a buffer solution was obtained. (i) Calculate the pH of the solution at point C. (ii) Write equations to show how this solution at point C reacts with small amounts of hydrogen ions and hydroxide ions. (iii) When 2 cm3 of 0.1 mol dm–3 HCl is added to the buffer solution at Point C, calculate the pH of the resulting solution. [6] B x pH Volume of NaOH added / cm C 3 210 x Page 4 of 10

2. (c) C6H5CH2Br can be synthesised from C 6H5CH3 through the following reaction pathways: CH3 CH2OH D CH2Br Step I Step II Step III Reaction Route 1 Reaction Route 2 (i) State the reagents and conditions required for steps I, II and III. Hence, deduce the structure of Compound D. (ii) Suggest reagents and conditions for Reaction Route 2 whereby the synthesis can be completed in one step. (iii) Comparing Reaction Route 1 and Reaction Route 2, which one is a better synthetic pathway? Explain your choice. (iv) Suggest a chemical test to confirm the presence of in the s ynthesis. [8] [Total marks: 20] CH2Br Page 5 of 10

3. (a) Phosphorus forms 2 chlorides, PC l3 and PC l5. The pentachloride is prepared by reacting PCl3 with dry chlorine. PCl3 + Cl2  PCl5 ΔH = –124 kJ mol–1 The preparation is carried out in a cooled flask under anhydrous conditions. (i) Suggest two reasons why a cooled flask is used. (ii) Give a reason for the use of anhydrous conditions. Include any relevant equations. [4] (b) Describe and explain what happens in the following experiment and write balanced equations, including state symbols, for the reactions that occur. Aqueous sodium chloride and aqueous silver nitrate are mixed and aqueous ammonia is then added. [3] (c) Using your knowledge of the reactions of solid sodium chloride, bromide and iodide, predict the gaseous products that will be formed when concentrated sulphuric acid is warmed with solid sodium astatide (NaAt). Write equations, including state symbols, for all the reactions occurring with sodium astatide. [2] (d) Hydrogen chloride is another very commonly used chlorine-containing reagent in the laboratories for simple reactions as shown below: When P, C 6H10O4, is heated with aqueous sodium hydroxide, compound Q, C2H6O2, and sodium ethanoate are formed. When 1 mol of Q reacts with 1 mol of hydrogen chloride, R, C 2H5OCl, is formed. R gives S, C3H5ON on heating with ethanolic potassium cyanide. When S is heated with dilute HC l, an optically inactive liquid T, C 3H6O3, is obtained. On heating T with A l2O3, a liquid U, C 3H4O2, is formed. U rapidly decolourises aqueous bromine. Deduce the structural formulae of compounds P to U, giving your reasoning. [11] [Total marks: 20] Page 6 of 10

4. (a) Hydrogen peroxide reacts with iodide ions in acidic solution as shown below. H2O2(aq) + 2H+(aq) + 2I(aq) → 2H2O(l) + I2(aq) In a series of experiments, the reaction was carried out with different concentrations of the 3 reagents and the following results were obtained. Expt No. [H2O2] / mol dm-3 [H+] / mol dm-3 [I ] / mol dm-3 Relative initial rate / mol dm-3 s-1 1 0.020 0.060 0.060 1.00 2 0.020 0.050 0.050 0.833 3 0.020 0.050 0.060 1.00 4 0.025 0.050 0.050 1.042 (i) Use the data to deduce the order of reaction with respect to each reagent. Explain your answers and write a rate equation. (ii) Two different mechanisms have been suggested for this react