2022 RI Prelim P3 QP

© Raffles Institution 2022 9729/03/S/22 [Turn Over RAFFLES INSTITUTION 2022 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/03 Paper 3 Free Response 16 September 2022 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class 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. 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. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. 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. For Examiner’s Use Section A Section B Total 1 / 17 (Circle the question you have answered) / 80 2 / 23 4 / 20 3 / 20 5 / 20 This document consists of 40 printed pages.

2 © Raffles Institution 2022 9729/03/S/22 For examiner’s use Section A Answer all the questions in this section. 1 Ionic chlorides have several uses such as in the manufacturing of rubber and as a dietary supplement. (a) 20.0 cm 3 of 0.010 mol dm −3 KCl(aq) was accidentally mixed with 20.0 cm 3 of 0.010 mol dm−3 Na2CO3(aq). To separate the chloride and carbonate ions, solid AgNO 3 was added to the mixture to precipitate the maximum amount of AgCl without precipitating Ag2CO3. [Ksp of AgCl = 2.0  10−10 mol2 dm–6, Ksp of Ag2CO3 = 8.1  10−12 mol3 dm−9 at 25 C] (i) Determine the concentration of Ag+ ions just before precipitation of Ag2CO3. Hence, calculate the concentration of chloride ions remaining in the final solution. [3] (ii) The separation of ions is considered effective if more than 98% of the chloride ions have been precipitated before the precipitation of Ag2CO3. Using your answer to (a)(i), determine whether effective separation has been achieved. [1] ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2022 9729/03/S/22 [Turn Over 3 For examiner’s use (b) CaCl2 and BaCl2 have different lattice structures. Fig. 1.1 shows the structure of the repeat unit in a crystal of CaCl2 and in a crystal of BaCl2. In CaCl2, the co-ordination number for Ca2+ is 6. In BaCl2, the co-ordination number for Ba2+ is 8. CaCl2 BaCl2 Fig. 1.1 (i) Suggest what is meant by the term co-ordination number when used to refer to a crystal lattice. [1] (ii) Suggest why Ca2+ and Ba2+ form chlorides with different co-ordination numbers. [1] (iii) The lattice energy of CaC l2 is expected to be more exothermic than that of BaC l2. However, the melting point of CaCl2 is lower than that of BaCl2. Suggest why. [1] ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………. Ca2+ Cl− Ba2+ Cl−

© Raffles Institution 2022 9729/03/S/22 4 For examiner’s use (c) Anhydrous CaCl2 absorbs water readily and is commonly used in the laboratory as a drying agent. (i) The absorption of water by anhydrous CaCl2 is shown below. CaCl2(s) + xH2O(l) ⎯→ CaCl2 • xH2O(s) ∆H1 Deduce the signs of the changes in entropy and Gibbs free energy for the above process. Hence, state and explain the sign of ∆H1. [2] (ii) Define the term lattice energy of calcium chloride. [1] (iii) Using the data in Table 1.1 and relevant data from the Data Booklet, construct an energy level diagram and calculate the lattice energy of calcium chloride. [4] Table 1.1 standard enthalpy change of formation of anhydrous CaCl2(s) −796 kJ mol−1 standard enthalpy change of formation of Cl−(g) −242 kJ mol−1 standard enthalpy change of atomisation of Ca(s) +177 kJ mol−1 ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2022 9729/03/S/22 [Turn Over 5 For examiner’s use ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

© Raffles Institution 2022 9729/03/S/22 6 For examiner’s use (d) Describe the reactions of the chlorides, AlCl3 and PCl5, with water. Write equations for all reactions that occur and suggest the pH of the resulting solutions. [3] ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ……………………………………………………