2023 RI Prelim P3 Question Paper

RAFFLES INSTITUTION 2023 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/03 Paper 3 Free Response 20 September 2023 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 / 20 (Circle the question you have answered) / 80 2 / 20 4 / 20 3 / 20 5 / 20 This document consists of 27 printed pages and 1 blank page.

2 © Raffles Institution 2023 9729/03/S/23 [Turn Over Section A Answer all the questions in this section. 1 (a) Elemental silicon does not occur naturally and is obtained from SiO2 in rocks. (i) Silicon has a similar structure to diamond. However, the melting point of silicon at 1414 °C is lower than that of diamond at 3550 °C. Explain this difference with reference to the structure and bonding of silicon and diamond. [2] (ii) Describe the difference in the acid-base behaviour of A l2O3 and SiO 2. Write relevant equations to illustrate your answer. [3] ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………

3 © Raffles Institution 2023 9729/03/S/23 [Turn Over (b) The standard enthalpy change of formation, ∆Hf, of SiO2 and CO are listed in Table 1.1. Table 1.1 Reactions 1 and 2 show two possible ways of extracting Si from SiO2. reaction 1 SiO2(s) → Si(s) + O2(g) ∆G2500K = +450.9 kJ mol−1 reaction 2 SiO2(s) + 2C(s) → Si(s) + 2CO(g) ∆S = +361 J mol−1 K−1 compound ∆Hf / kJ mol−1 SiO2 −910.9 CO −110.5 (i) In practice, the extraction of Si from SiO2 is carried out at 2500 K. Calculate ∆G for reaction 2 at 2500 K and explain why reaction 2 is preferred for the extraction of Si from SiO2. Assume that ∆H and ∆S are independent of temperature. [3] (ii) Comment on the sign of ∆S of reaction 2 with respect to the reaction. [1] ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………

4 © Raffles Institution 2023 9729/03/S/23 [Turn Over (c) Using the data in Table 1.2 and the Data Booklet, calculate the lattice energy of Ca2SiO4 with the aid of an energy cycle. You may assume that the lattice of Ca2SiO4 comprises Ca2+ and SiO44− ions. Table 1.2 value / kJ mol−1 standard enthalpy change of atomisation of Ca(s) +121 standard enthalpy change of formation of Ca2SiO4(s) −2306 enthalpy change of the following reaction Si(s) + 2O2(g) + 4e− → SiO44−(g) +13872 [3] …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ……………………………………………………………………………………………………..

5 © Raffles Institution 2023 9729/03/S/23 [Turn Over (d) Rusting occurs when iron is exposed to oxygen and water. The initial process involves the oxidation of Fe to Fe 2+ ions and the reduction of O 2 to OH− ions. The migration of ions eventually results in the formation of rust. Use the table of standard redox potentials given in the Data Booklet to answer the questions below. (i) Define the term standard electrode potential, E, of a half-cell. [1] (ii) Write the overall equation for the initial process of rusting and calculate its Ecell. [2] (iii) Use your answer in (d)(ii) to calculate the standard Gibbs free energy change, ∆G, for the initial process of rusting. [1] (iv) Using information from the Data Booklet where relevant, explain why iron in the following objects rust slowly or not at all. (I) A well-oiled iron bicycle chain. (II) A piece of zinc is attached to the iron hull of a ship. [2] ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………

6 © Raffles Institution 2023 9729/03/S/23 [Turn Over (e) The process of coating aluminium objects with aluminium oxide, A l2O3, via electrolysis is called anodising. Draw a labelled diagram of the electrolysis cell used for the anodising of aluminium. Include details of the cathode, anode and electrolyte. [2] …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ………………………………………………………