JPJC 2023 Prelim P2 QP

© Jurong Pioneer Junior College [Turn Over NAME CLASS 22S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2023 CHEMISTRY 9729/02 Paper 2 Structured Questions September 2023 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and index number in the spaces at the top of this page. Write in dark blue or black pen. You may use a 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. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 13 2 10 3 10 4 13 5 16 6 13 Penalty (delete accordingly) Lack 3sf in final answer –1 / NA Missing/wrong units in final ans –1 / NA Bond linkages –1 / NA Total 75 This document consists of 19 printed pages and 1 blank page.

2 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2023 Answer ALL the questions in the spaces provided. 1 (a) Halogens can react with alkanes to form halogenoalkanes. The boiling points of a few halogenoalkanes, in Kelvin, are given in Table 1.1. Table 1.1 compound boiling point / K CH3F 195 CH3Cl 249 CH3CH2F 236 For Examiner’s Use (i) Comment on the relative bond polarity of C −F bond in CH3F and C−Cl bond in CH3Cl. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (ii) Explain the difference in boiling point between CH3F and CH3Cl. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (iii) Both CH3Cl and CH3CH2F are isoelectronic. Explain the difference in boiling point between CH3Cl and CH3CH2F. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1]

3 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2023 [Turn Over (b) Halogens can react to form interhalogen compounds such as F3. Consider a molecule of F3, the central atom is surrounded by five pairs of electrons in a trigonal bipyramidal arrangement. There are three electron pairs arranged on the same plane in equatorial positions and two electron pairs arranged perpendicular to the plane in axial positions. Three possible different molecular arrangements of F3 are shown in Table 1.2. For Examiner’s Use Table 1.2 Lone pairs in axial positions. Lone pairs in equatorial positions. Lone pairs in axial and equatorial positions. number of lone pairs at 90 relative to one another 0 0 1 number of bond pair and lone pair at 90 relative to one another 3 relative stability (i) For each structure, count the number of lone pair and bond pair that are 90 relative to one another. Fill the numbers in Table 1.2. [1] (ii) Apply the principles of the Valence Shell Electron Pair Repulsion (VSEPR) theory to deduce the relative stability of these three possible arrangements. State the “ most stable” structure and the “ least stable” structure in Table 1.2. [2]

4 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2023 (c) Peroxydisulfate ions, S2O82−, can react with iodide ions, I−, to form sulfate ions, SO42−, and iodine in a redox reaction. S2O82−(aq) + 2I−(aq) → 2SO42−(aq) + I2(aq) For Examiner’s Use (i) Draw a fully labelled diagram of the electrochemical cell you would set up in order to measure a E cell value for this reaction. In your answer, include the polarity of each electrode and the direction of electron flow in the external circuit. [3] (ii) Using relevant data from the Data Booklet, calculate G, in kJ mol−1, for the above reaction. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [2] (iii) Using your answer in (c)(ii), deduce whether the above reaction is exothermic or endothermic. Explain your answer as fully as you can. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [2] [Total: 13]

5 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2023 [Turn Over 2 (a) Data concerning the Group 2 elements, at 298 K, are given in Table 2.1. Further data may be found in the Data Booklet. No calculation is required. For Examiner’s Use Table 2.1 Mg Ca Sr Ba Hhyd of M2+ / kJ mol−1 −1980 −1650 −1480 −1365 solubility of MSO4 / mol per 100 cm3 water 1.8 × 10−1 4.7 × 10−3 7.1 × 10−5 9.4 × 10−7 (i) When a salt such as Group 2 sulfate dissolves in water, the lattice energy must be overcome. Explain how the magnitude of the lattice energy, HLE, of Group 2 sulfates will change from MgSO4 to BaSO4. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [2] (ii) Explain why the Hhyd of M2+ becomes less negative from Mg2+ to Ba2+. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [1] (iii) By considering the relationship between Hsol, HLE and Hhyd, suggest a reason to explain the trend in the solubility of the Group 2 sulfates. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [2] (iv) 100 cm 3 of 0.0100 mol dm −3 aqueous calcium chloride was added to 100 cm3 of 0.0200 mol dm −3 aqueous sodium sulfate. Use relevant data in Table 2.1 to deduce whether precipitation of calcium sulfate will occur. [2]

6 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2023 (b) The equation for the standard enthalpy change of formation of a gaseous sulfate ion is shown. S(s) + 2O2(g) + 2e− → SO42−(g) Hf (SO42−(g)) Using relevant data in Table 2.2 and the Data Booklet, complete the energy level diagram in Fig. 2.3 and use it to calculate Hf (SO42−(g)). Table 2.2 enthalpy change value / kJ mol−1 lattice energy of BaSO4(s) −2469 standard enthalpy change of formation of BaSO4(s) −1473 standard enthalpy change of atomisation of Ba(s) +180 standard enthalpy change of atomisation of S(s) +279 standard enthalpy change for S(g) → S2−(g) +440 standard enthalpy change for O(g) → O2−(g) +657 For Examiner’s Use

7 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2023 [Turn Over Fig. 2.3 [3] [Total: 10] 3 The first stage of the Contact process for manufacturing concentrated sulfuric acid is to produce SO3 from SO2 and O2. 2SO2(g) + O2(g)  2SO3(g) For Examiner’s Use (a) (i) State two conditions necessary for an effective collision between reactant molecules. …………………………………………………………………………………… …………………………………………………………………………………… [1] (ii) Explain the effect o f increasing total pressure, at constant temperature, on the rate of production of SO3(g) and the yield of SO3(g). rate ……………………………………………………………………………… …………………………………………………………………………………… [2] energy /kJ mol−1 0 BaSO4(s)

8 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2023 …………………………………………………………………………………… yield …………………………………………………………………………….. …………………………………………………………………………………… …………………………………………………………………………………… (b) 2.00 mol of SO2(g) and 1.00 mol of O 2(g) was introduced in a container with a suitable catalyst, at constant temperature