2022 TJC Prelims H2 Paper 3 Free Response Qns and Ans

9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2022 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME WORKED SOLUTIONS CENTRE NUMBER S INDEX NUMBER Chemistry 9729/03 Paper 3 Free Response Questions 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 23 printed pages and 1 blank page. 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] It acts as a Bronsted-Lowry base to abstract H+ from the carboxylic acid.[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] • Electrophilic addition Name of mechanism [1] Mechanism [2] δ+ δ-

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 (iii) Sketch a well -labelled reaction pathway diagram for the reaction in Step 2, given that the reaction is exothermic. [2] Diagram & labelling:[1] Ea1, Ea2 & ∆H0: [1] (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]  (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) … (1) Hb(aq) + 4CO(aq) Hb(CO)4(aq) … (2) 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] Providing O 2 forms Hb(O 2)4(aq), which ✓ shifts the position of 1 st equilibrium to the right, ✓ removing Hb(aq) from the bloodstream. By Le Chatelier’s Principle, the ✓ position of 2nd equilibrium will shift left to ✓ increase amount of Hb(aq), thus reducing the amount of Hb(CO)4(aq) in the body. 2✓: [1] (c) The water-gas shift reaction is used to produce hydrogen gas industrially by reacting carbon monoxide with water vapour. Energy + I- Reaction Progress Ea1 Ea2 ∆H0

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 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] CO (g) + H2O (g) ⇌ CO2 (g) + H2 (g) Initial P / atm 0.0197 0.0394 0 0 ∆ in P / atm –0.0191 –0.0191 +0.0191 +0.0191 Eqm P / atm 0.0006 0.0203 0.0191 0.0191 Working [1] p (0.0191)(0.0191) 30.0 (0.0006)(0.0203) K == Answer [1] 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] G (300) = – RT ln Kp (300) = – (8.31)(300) ln (117000) = – 29090 J mol–1 [√] G (900) = – RT ln Kp (900) = – (8.31)(900) ln (1.978) = – 5101 J mol–1 [√] G (300) = H – (300)S = – 29090 J mol–1 ----- (1) allow ecf [√] G (900) = H – (900)S = – 5101 J mol–1 ----- (2) allow ecf [√] (1) – (2): S = – 40.0 J K–1 mol–1 (3 sf) allow ecf [1] include unit (iii) Comment on the magnitude of the calculated value of S. [1]

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 The magnitude is small as there is no change in the amount of gaseous molecules when reactants changed to products. Hence, there is little change in the number of ways that energy can be distributed over the molecules. (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] Boltzmann distribution diagram: [1] At higher temperatures, the proportion of molecules with kinetic energy greater than or equal to activation energy increases [√]. Frequency of effective collision increases [√], rate constant increases [√], rate increases [√]. 2√: [1] [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] G: CO2 A: CuO B: Cu2O C: [Cu(H2O)6]2+ 1 tick for each answer. 4 ticks − [2] 2 to 3 ticks − [1] (ii) Suggest, with reason, the colour of solid F. [2] Oxidation of copper in F, CuI = +1 Electronic configuration of Cu+: [Ar] 3d10 The d orbitals of Cu+ ion are fully filled. 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

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