CJC Prelim P3

9729/03/CJC JC2 Preliminary Examination 2018 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/03 Paper 3 Free Response Friday 24 August 2018 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class 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. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. At the end of examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 10 printed pages. Catholic Junior College JC2 Preliminary Examinations Higher 2

2 9729/03/CJC JC2 Preliminary Examination 2018 Section A Answer all the questions in this section. 1 Propene is a colourless gas that is produced in large quantities by the petrochemical industry. It is used in the production of synthetic rubber and as a propellant in aerosols. (a) When propene reacts with HBr, 2-bromopropane is produced as the major product. CH2=CHCH3 + HBr → CH3CHBrCH3 (i) Describe the mechanism of the above reaction, using curly arrows to show the movement of electrons. [4] (ii) When propene reacts with BrC l, 1-bromo-2-chloropropane is produced as the major product. CH 2=CHCH3 + BrCl → CH2BrCHClCH3 With reference to your answer in (i), explain why the two reactions give major products with bromine in different positions. [2] (iii) The product of the reaction in (ii) has a chiral carbon, but it is optically inactive. Explain why this is so. [2] (b) 2-bromopropane reacts with hot aqueous sodium hydroxide, whereas 2-bromopropene does not. Suggest reasons for this difference in reactivity. [2] (c) Propene can undergo mild oxidation in the presence of cold acidified potassium manganate(VII), to give CH 2(OH)CH(OH)CH3. (i) State the IUPAC name of the product of the above reaction. [1] (ii) Construct the half ‒equation for the oxidation of propene as described above. [1] (iii) Hence, write the equation for the overall reaction, showing clearly the stoichiometry of reaction between propene and manganate(VII) ions. [1] (d) At room temperature and pressure, 28 cm 3 of propene was bubbled into 40.0 cm3 of 0.0200 mol dm‒3 acidified KMnO4(aq). The resulting solution was titrated against Fe2+(aq) of concentration 0.0750 mol dm‒3. (i) State the colour change at endpoint for this titration. [1] (ii) Given that 5 moles of Fe 2+ react with 1 mole of MnO4 ‒, determine the volume of Fe2+(aq) needed to reach endpoint. [3] (e) A mixture of propene ( Mr = 42.0) and 2-bromopropane (Mr = 122.9) kept in a vessel of volume of 3.60 dm3 maintained at 75 oC exerts a pressure of 1.66 x 105 Pa. The mole fraction of propene in the mixture is 0.28. Find the mass of the mixture of gases. [3] [Total: 20]

3 9729/03/CJC JC2 Preliminary Examination 2018 [Turn over 2 Copper is a transition metal, and is one of the metals used to make coins, along with silver and gold. Most copper is used in electrical equipment such as wiring and motors. It also has uses in construction and industrial machinery. (a) One of the characteristic properties of copper is its ability to form coloured aqueous complexes shown in Fig 2.1. Fig. 2.1 (i) State the complex ion A. [1] (ii) Draw the structure of complex ion A. [2] (iii) EDTA 4− is a hexadentate ligand. Deduce the formula of the complex ion B. [1] (iv) Suggest why complex B is readily formed from complex A. [1] (v) Explain why aqueous Cu2+ ions are blue in colour. [3] (vi) The numerical value of the solubility product, Ksp of Cu(OH)2 is 2.20 x 10−20 at 25 oC. Write the expression for Ksp and state its units. Calculate the solubility of Cu(OH)2 at 25 oC. [3]

4 9729/03/CJC JC2 Preliminary Examination 2018 (b) When an aqueous solution of ammonia is shaken with an organic solvent, trichloromethane, at room temperature, the following equilibrium is set up between the two immiscible liquids. NH 3(aq) ⇌ NH3(organic) equilibrium 1 The equilibrium constant, Kc, for this reaction is 0.04. Water that is contaminated with copper(II) sulfate is harmful to crops, animals and humans. Some water that has been contaminated with 0.100 mol dm−3 copper(II) sulfate was allowed to reach dynamic equilibrium at room temperature with an excess of ammonia and trichloromethane. The aqueous layer was found to contain 0.660 mol dm−3 of ammonia, some of which reacted with Cu2+(aq) according to the following equation Cu2+(aq) + nNH3 → [Cu(NH3)n]2+ The organic layer contained 0.0104 mol dm−3 of ammonia. (i) Define the term dynamic equilibrium. [1] (ii) Explain the relative solubility of ammonia in water and trichloromethane in terms of the intermolecular forces involved. [2] (iii) Hence, in terms of the position of equilibrium, explain why the value of Kc for equilibrium 1 is relatively low. [1] (iv) By calculating [NH3(aq)] present, show that the value of n in [Cu(NH 3)n]2+ is 4. [2] (c) Another characteristic property of transition metal ion is its ability to catalyse reactions. The rate of the reaction between iodide and peroxodisulfate(VI) ions S2O82−(aq) + 2I−(aq) ⎯→ 2SO42−(aq) + I2(aq) is very slow. If a small amount of aqueous transition metal, cobalt( II) ions is added to the mixture, the rate of reaction increases. (i) By considering relevant half equations from the Data Booklet , construct chemical equations to show how cobalt(II) ions behave as a catalyst in this reaction. No calculation is required. [2] (ii) Suggest another transition metal ion, which will be able to catalyse this reaction. [1] [Total: 20]

5 9729/03/CJC JC2 Preliminary Examination 2018 [Turn over 3 (a) Analgesics are medicines used to relieve pain. The two most common analgesics in the market are aspirin and paracetamol. Their structures and corresponding pKa values are shown in Table 3.1. Table 3.1 Name of analgesic Structure p Ka value Aspirin 3.49 Paracetamol 10.30 (i) Explain the difference in the p Ka values between aspirin and paracetamol. [2] Paracetamol can be synthesised from phenol in a 3-step process shown in Fig 3.1. Fig. 3.1 (ii) Suggest the structures for intermediates X and Y. [2] (iii) Suggest the reagents and conditions required for step 1 to 3. [3]

6 9729/03/CJC JC2 Preliminary Examination 2018 (b) The use of aspirin has been shown to increase the risk of gastrointestinal bleeding. Hence, buffering agents are added to aspirin to mitigate the problem of gastrointestinal bleeding. These buffering agents work by preventing the aspirin from concentrating in the walls of the stomach. Common buffering agents used include magnesium hydroxide, Mg(OH)2, and calcium carbonate, CaCO3. Some relevant standard enthalpy change of hydration values and lattice energy of Mg(OH)2, are shown in Table 3.2. Table 3.2 Enthalpy term Value / kJ mol–1 Standard enthalpy change of hydration of Mg2+(g) –1926 Standard enthalpy change of hydration of OH– (g) –460 Lattice energy of Mg(OH)2(s) –2998 Using relevant data in the table above, construct an energy level diagram to determine the standard enthalpy change of solution, ΔHsolo, of Mg(OH) 2 in water. [3] (c) Compound A is an unsaturated ester containing a benzene ring and has a molecular formula of C 16H22O3. A reacts with neutral FeC l3 to give violet colouration. A reacts with H 2 in the presence of Ni t