2024 Prelims TJC H2 Chem P3 (QP)

9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS CENTRE NUMBER S INDEX NUMBER Chemistry 9729/03 Paper 3 Free Response Questions 11 September 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, 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. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. 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 the 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 28 printed pages. For Examiner’s Use Paper 3 Q1 /19 Q2 /19 Q3 /22 Q4 /20 Q5 /20 Total /80

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 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) In Group 14 of the Periodic Table, t he elements at the top of the group, carbon to germanium, have very different properties from those at the bottom, tin and lead. For instance, carbon to germanium tend to adopt oxidation states of +4, whereas the heavier elements, such as tin and lead, exhibit the +2 oxidation states. (i) Table 1.1 shows the melting points of the elements of Group 14. Table 1.1 element C Si Ge Sn Pb melting point / C >3550 1410 937 232 327 Carbon, silicon and germanium each forms a solid with the same type of structure. Using structure and bonding and the information from the Data Booklet, suggest why the melting points of these elements decrease from carbon to germanium. [2] Carbon forms many allotropes such as graphite and diamond . Recent scientific research has found that replacing the graphite electrodes with graphene in lithium-ion batteries can extend battery life. Graphene is a single, one atom thick layer of graphite. (ii) Explain why graphene can conduct electricity along the plane. [1] (iii) State and explain how you would expect the bond strength of carbon-carbon bonds in graphene to differ when compared with that in diamond. [2]

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over (b) Carbon forms carbide anion, C22– in calcium carbide while silicon mostly forms Si 4+ ions. Calcium carbide is a crystalline solid with a melting point of approximately 2160 °C. (i) Draw the dot-and-cross diagram of C22–. [1] (ii) When some calcium carbide is added to excess water with a drop of Universal Indicator, ethyne gas, C2H2, is produced. The solution changes from green to blue after the reaction is complete. Write an equation, with state symbols, for this reaction. [2] (iii) In a particular experimental set-up, a beam of 12C22– ions was deflected by an angle of -2.45°. Assuming an identical set of conditions, calculate the angle of deflection for 28Si4+ ions. [2]

4 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (c) Using the data from Data Booklet , describe and explain the reducing strength of Group 2 elements from magnesium to strontium. [3] (d) Aluminium chloride is used as a catalyst for the reaction between methylbenzene and 2-chloropropane to form two constitutional isomers L and M with the formula C10H14. (i) Suggest the mechanism for this reaction to form the major product, L. Show all charges and relevant lone pairs and show the movement of electron pairs using curly arrows. [3] (ii) L and M are formed in a 60:40 ratio. Suggest why L is the major product. [1]

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over (e) (i) Write an equation for the reaction of with acidified KMnO4. [1] (ii) Name the oxidised product formed in (e)(i). [1] [Total: 19]

6 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 2 Many chemical processes release waste products into the atmosphere. Scientists are developing new catalysts to convert these emissions into useful products, such as methanol which can be used as a fuel. An equation for the synthesis of methanol is given below. CO2(g) + 3H2(g) ⇌ CH3OH(g) + H2O(g) ΔH = – 49 kJ mol-1 (a) (i) State and explain the effect on the position of equilibrium when the temperature is increased. [2] (ii) State and explain the effect on the position of equilibrium when the pressure is increased. [1] (iii) Write an expression for Kp of the reaction. [1] 1.0 mol of carbon dioxide and 3.0 mol of hydrogen were sealed in a container. After the mixture had reached equilibrium, at a pressure of 500 kPa, the amount of methanol produced was 0.86 mol. (iv) Determine the mole fraction of methanol when the system reached equilibrium. [2] (v) Hence, calculate the Kp value, stating its units. [2] (vi) Suggest one possible environmental advantage of this reaction. Explain your answer. [1]

7 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over (b) The standard enthalpy change of formation of some species are given in Table 2.1. Table 2.1 compound ΔHf/ kJ mol–1 CO2(g) –394 H2O(g) –242 (i) Define standard enthalpy change of formation. [1] (ii) Write an equation to represent the standard enthalpy change of formation of CH3OH(g). [1] (iii) Use the enthalpy change of reaction for the synthesis of methanol and the data provided in Table 2.1 to calculate the standard enthalpy change of formation of CH3OH(g). [1]

8 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (c) (i) State two assumptions of ideal gas behaviour. [1] (ii) Fig. 2.1 shows the graphical plot of pV = nRT for CO 2(g) at 500K as a function of pressure. On the same axes provided in Fig 2.1, sketch the graph for H2O(g) at 500K. [1] Fig. 2.1 (d) Carbon dioxide can be formed by thermal decomposition of carbonates and hydrogen carbonates. The thermal decomposition of potassium hydrocarbonate, KHCO 3, proceeds according