2025 JC2 Prelims H2 Chem Paper 2 QP TJC

9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2025 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS / 24 CENTRE NUMBER S INDEX NUMBER Chemistry 9729/02 Paper 2 Structured Questions 3 September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, CG, centre and index number in the space provided at the top of this page. 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. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in bracket [ ] at the end of each question or part question. This document consists of 22 printed pages and 2 blank pages. For Examiner’s Use Q1 Q2 Q3 Q4 Q5 Q6 Total

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 1 In 1932, the American chemist Linus Pauling developed the most common scale of relative electronegativity (EN) values for the elements. The Pauling EN values of elements can be used to predict the chemical properties of compounds. The EN values of four Period 3 elements are given in Table 1.1. Table 1.1 Element Sodium Aluminium Phosphorus Chlorine Pauling EN value 0.93 1.61 2.19 3.16 l (a) (i) Explain the difference in the Pauling electronegativity values of Na and Cl. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... .....................................................................................................................................[2] The ionic character of a bond is directly related to the electronegativity difference ( EN) between the bonded atoms. Fig. 1.1 shows the plot of percent ionic character against EN for NaCl. Fig. 1.1 (ii) Using the values in Table 1.1, calculate EN for AlCl3 and PCl5 respectively. Hence plot the percent ionic character of AlCl3 and PCl5 on Fig. 1.1. Label your points clearly. [2]

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over (iii) Explain the difference in bonding for NaCl and PCl5 in terms of electronegativity. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... .....................................................................................................................................[2] (b) (i) The polarity of bonds in covalent molecules is also affected by EN. SeF4 and BrF3 are two fluorine-containing molecules. State whether SeF4 or BrF3 contains covalent bonds with a higher ionic character. Higher ionic character .................................................................................................[1] (ii) Using VSEPR theory, predict and explain the shape and bond angles of SeF4. Illustrate the shape of SeF4 with an appropriate diagram. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... .....................................................................................................................................[3] [Total: 10]

4 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 2 PCl5 is a Period 3 chloride commonly used as a chlorinating agent and catalyst in making organic compounds. Industrial production of PCl5 involves the reaction of Cl2 with PCl3. Reaction (1) PCl3(g) + Cl2(g) ⇌ PCl5(g) (a) Suggest, with an explanation, how the position of equilibrium and the composition of the equilibrium mixture might change when chlorine is added to the equilibrium system. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... ................................................................................................................................................[2] x mol of Cl2 gas is added to a 2 dm3 vessel containing an equilibrium system of 0. 4 mol of PCl3, 0.25 mol of Cl2 gas and 1.2 mol of PCl5. The new equilibrium amount of PCl5 is 1.28 mol. (b) (i) Write the Kc expression for reaction (1), giving its units. [1] (ii) Using the information given above, calculate Kc. [1] (iii) Hence calculate x, the amount of Cl2 added. [2]

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over (c) Period 3 oxides follow a similar trend in bonding as the Period 3 chlorides. Describe the action of water on the oxides of sodium, alumin ium and phosphorus, write equations for any reactions that occur, and suggest the pH of each solution formed. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... ................................................................................................................................................[3] [Total: 9]

6 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim