2022 TJC Prelims H2 Paper 3 Free Response QP

9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2022 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CIVICS CLASS CENTRE NUMBER S INDEX NUMBER Chemistry 9729/03 Paper 3 Free Response 14 September 2022 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do NOT open this booklet until you are told to do so. Write your name, civics class, centre number and index 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. 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. The number of marks is given in brackets [ ] at the end of each question or part question This document consists of 28 printed pages. For Examiner’s Use Paper 3 Q1 /18 Q2 /20 Q3 /22 Q4 /20 Q5 /20 Total /80

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Section A Answer all the questions in this section. 1 (a) Iodolactonisation reaction was first reported by M. J. Bougalt in 1904 and has since become one of the most effective ways to synthesise lactones. An example of the iodolactonisation is the reaction of 4-pentenoic acid as shown in Fig 1.1. Compound X Fig 1.1 Two simplified steps in the iodolactonisation mechanism are given in Fig 1.2. Compound X Fig 1.2 (i) Suggest the role of HCO3- in step 1. [1] (ii) Suggest the mechanism for reaction taking place in step 2. Show all charges and relevant lone pairs and show the movement of electron pairs by using curly arrows. [3] (iii) Sketch a well-labelled reaction pathway diagram for the reaction in step 2, given that the reaction is exothermic. [2] (iv) Suggest the structural formulae of the final organic product formed when CH2=CHCH(CH3)CH2CH2COOH undergoes iodolactonisation in a similar process in Fig 1.1. [1]

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over

4 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (b) Carbon monoxide is one of the most widespread and dangerous industrial hazards. The formation of carboxyhaemoglobin, Hb(CO) 4, takes place much more readily than the formation of oxyhaemoglobin, Hb(O2)4. Hb(aq) + 4O2(aq) Hb(O2)4(aq) Hb(aq) + 4CO(aq) Hb(CO)4(aq) A treatment method for carbon monoxide poisoning is to provide the patient with pure oxygen gas over a period of time. With reference to the equations given above, explain why this is a suitable treatment method. [2] (c) The water-gas shift reaction is used to produce hydrogen gas industrially by reacting carbon monoxide with water vapour. CO(g) + H2O(g) CO2(g)+ H2(g) An evacuated tank was initially filled with 0.0197 atm of CO and 0.0394 atm of H 2O at 600 K. It was sealed and left to stand. At equilibrium, the partial pressure of CO 2 was found to be 0.0191 atm. (i) Calculate the value of Kp at 600 K. [2] Table 1.1 shows how the value of Kp varies with temperature. Table 1.1 T / K 300 900 1500 value of Kp 1.170 x 105 1.978 0.2195 1 (ii) The Gibbs free energy, G (in J mol –1), and the equilibrium constant, Kp, of a reaction are related by the following equation: G = – RT ln Kp, where R is the molar gas constant and T is the temperature in Kelvins. Using the given values of Kp, calculate the values of G at 300 K and 900 K. Hence, determine the value of S for the water-gas shift reaction. (Assume that both H and S are independent of temperature.) [3] (iii) Comment on the magnitude of the calculated value of S. [1] (iv) With the aid of a sketch of the Boltzmann distribution, explain how an increase in temperature affects the rate of water-gas shift reaction. [3]

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over [Total:18]

6 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 2 Copper is a typical transition element with more than one oxidation state. Many of its compounds have colours in the blue-green-yellow part of the visible spectrum. The following reaction scheme shows the chemistry of some copper-containing species. (a) (i) A and B are both compounds of copper and oxygen only. Cu2SO4 can be made from B under certain anhydrous conditions. The oxidation number of copper in B is the same as in Cu2SO4. Identify gas G, and write the formula of the copper-containing species in A to C. [2] (ii) Suggest, with reason, the colour of solid F. [2] CuCO3(s) black solid AG + red solid B Cu2SO4 heat blue solution C KI(aq) gas heat above 800 oC blue solid D dark blue solution E NH3(aq) in excess NH3(aq) violet solution H ethane-1,2-diamine (en) solid F dil H2SO4 H2O

7 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over (b) Explain the transformations from C to E in terms of the competing equilibria and the type of reaction that has occurred. Include equations and the formulae of all copper -containing species. [4]

8 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (c) Like many organic compounds, transition metal complexes also exhibit stereoisomerism, namely cis-trans isomerism and enantiomerism. For example, [Cu(en)2(H2O)2]2+, the complex ion present in H, has three stereoisomers, X, Y and Z. One of these stereoisomers, X, is shown below. ( represents the en ligand.) X X and Z are cis-trans isomers, while Y is an enantiomer of X. Draw and label clearly the three -dimensional diagrams of Y and Z. You should use to represent the en ligand. [3] N N Cu OH2 OH2 N N N N 2+ N N

9 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over (d) Selective precipitation is a technique of separating ions in an aqueous solution by using a reagent that precipitates one or more of the ions, while leaving other ions in solution. In the case of Cu2+ ions, the separation is achieved by adjusting the pH so that only Cu2+ ions are precipitated. In an experiment, a student adds sodium hydroxide gradually to a solution containing 0.100 mol dm–3 Cu2+ ions and 0.100 mol dm–3 Fe2+ ions. Relevant Ksp values are given in Table 2.1. Table 2.1 metal hydroxide Ksp / mol3 dm–9 Cu(OH)2 2.2  10–20 Fe(OH)2 8.0