2020 JPJC Prelim Paper 2 (Question Paper)

1  Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2020 [Turn Over NAME CLASS 19S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2020 CHEMISTRY 9729/02 Higher 2 Paper 2 Structured Questions 17 September 2020 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and exam index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a HB pencil for any diagrams, 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. A Data Booklet is provided. 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 Paper Question Mark 2 1 13 2 9 3 14 4 12 5 6 6 21 Penalty (delete accordingly) Lack 3sf in final ans –1 / NA Missing/wrong units in final ans –1 / NA Total 75 This document consists of 21 printed pages.

2  Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2020 Answer all the questions in the spaces provided. 1 (a) The following graph below shows the second ionisation energies of Period 3 elements with consecutive proton number. For Examiner’s Use (i) Explain why the second ionisation energy generally increases from B to H. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] (ii) Which of the above elements, A to H, is aluminium? ………………………………………………………………………………… [1] (iii) Explain the following:  big drop in second ionisation energy from A to B  slight drop in second ionisation energy from C to D ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 C D E F G H A B 2nd Ionisation Energy/ kJ mol–1

3  Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2020 [Turn Over (b) Among the elements of Group 14, those towards the top, carbon to germanium, have very different properties from th ose at the bottom, tin and lead. For example, the melting points show a marked change after germanium. element C Si Ge Sn Pb mp / C >3550 1410 937 232 327 Carbon, silicon and germanium each form a solid with the same type of structure. (i) Explain why the melting points of these elements decrease from carbon to germanium. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [1] (ii) Carbon and silicon each form a tetrachloride. CC l4 has no reaction with water; SiCl4 reacts violently with water. Suggest an explanation for the inertness of CCl4 to water. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [1] (c) The chalcogens are Group 16 elements which form compounds with carbon . The properties of some of these compounds, along with CO 2, are given in the Table 1 below. Table 1 compound structure dipole moment boiling point / C CO2 O=C=O 0 sublimes CS2 S=C=S 0 46 COS S=C=O 0.71 –50 COSe Se=C=O 0.73 –22 (i) Explain, in terms of structure and bonding, the difference in the boiling point of CS2 and COS. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2]

4  Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2020 (ii) Explain why  CO2 has no overall dipole moment.  COSe has a greater dipole moment than COS. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] (d) Chalcogens also form compounds with halogens known as chalcohalides. One such compound is selenium tetrafluoride, SeF4, which is used as a fluorinating reagent in organic syntheses. Draw a ‘dot -and-cross’ diagram showing the electrons (outer shell only) in a SeF4 molecule. Use the VSEPR (valence shell electron pair repulsion) theory to predict its shape. [2] [Total:13]

5  Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2020 [Turn Over 2 (a) The key reaction during the Contact process for the manufacture of sulfuric acid is as follows. 2SO2(g) + O2(g) ⇌ 2SO3(g) A mixture of SO2 and O2 in a 2:1 molar ratio was introduced into a sealed vessel and heated to 450K. At equilibrium it was found that the total pressure was 4.2 atm, and the mole fraction of O2 was 0.0476. For Examiner’s Use (i) Write an expression for the equilibrium constant, Kp for this reaction. [1] (ii) Calculate the equilibrium partial pressures of O2, SO2 and SO3. [2] (iii) Calculate the value of Kp for the reaction at 450K. [1]

6  Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2020 (iv) Explain clearly the effect on the yield of SO3, when the volume of reaction mixture is reduced. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] (b) Due to the importance of the Contact process, the spontaneity of the reaction has been studied extensively. (i) Predict the sign of the entropy change for the Contact process reaction. Explain your answer clearly. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] (ii) The enthalpy change for the Contact process is exothermic. Hence, using the answer in (b)(i), explain why this reaction is only spontaneous at low temperature. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [1] [Total:9]

7  Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2020 [Turn Over 3 (a) A sample of ground copper powder was contaminated with zinc powder. Treatment of the sample with an excess of hydrochloric acid produced 126 cm3 of hydrogen gas, measured at a temperature of 300 K and a pressure of 1.00x105 Pa, by the reaction shown. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) The remaining copper was then reacted with acidified potassium manganate(VII), forming a blue solution containing Cu2+(aq). It was found that 24.00 cm3 of 0.2 mol dm3 of potassium manganate(VII) was required for complete oxidation of the copper. For Examiner’s Use (i) Calculate the mass o