2023 ASRJC H2 Chem Prelim P2 QP

ASRJC JC2 PRELIM 2023 9729/02/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2023 JC2 PRELIMINARY EXAMINATION NAME:______________________________ ( ) CLASS: 23 / _____ CHEMISTRY 9729/02 Paper 2 Structured Questions 14 September 2023 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and register 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. 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 Paper 2 1 /19 2 /9 3 /11 4 /17 5 /19 Total / 75 This document consists of 20 printed pages and 4 blank pages.

2 ASRJC JC2 PRELIM 2023 9729/02/H2 Answer all the questions. 1 The common chlorides of Period 3 elements are shown in Table 1.1. Table 1.1 Period 3 chloride NaCl AlCl3 SiCl4 PCl5 Bonding C Structure S pH of aqueous solution 3 (a) A 3.30 g sample of a Period 3 chloride is heated to 500 K in a sealed flask of 250 cm3. At this temperature, the chloride is a gas and the pressure in the flask is 323 kPa. Assuming the gas behaves ideally, calculate the Mr of the Period 3 chloride. Hence, use the chlorides given in Table 1.1 to deduce its formula. [2] (b) (i) Complete Table 1.1 by • identifying the bonding shown by each chloride under standard conditions. Use C = covalent, I = ionic, M = metallic • identifying the structure shown by each chloride under standard conditions. Use G = giant, S = simple • stating the pH of the aqueous solution of each chloride at 298 K. [3]

3 ASRJC JC2 PRELIM 2023 9729/02/H2 [Turn over (ii) At certain temperature, aluminium chloride exists as A l2Cl6 molecules. Draw the structure of Al2Cl6. State how the shape with respect to each Al atom changes from AlCl3 to Al2Cl6. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ……………………………………………………………………………………………… ………………………………………………………………………………………………. …………………………………………………………………………………...…………. …………………………………………………………………………………………... [2] (iii) SCl2 is also a chloride of Period 3 element. It is a cherry-red liquid that reacts vigorously with water to form a strongly acidic solution. Use this information to deduce the bonding and structure shown by SCl2. Structure: …………………………. Bonding: ………………………….. Explanation: ………………………………………………………………………………. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………[2]

4 ASRJC JC2 PRELIM 2023 9729/02/H2 SCl2 is formed when sulfur, S8, reacts with an excess of chlorine in a series of steps. step 1 S8(s) + 4Cl2(g) → 4S2Cl2(l) Hr = –58.2 kJ mol–1 step 2 S2Cl2(l) + Cl2(g) 2SCl2(l) Hr = –40.6 kJ mol–1 (iv) Calculate the enthalpy change of formation, Hf, of SCl2(l). 1 8 S8(s) + Cl2(g) → SCl2(l) Hf [2] (v) State the effect of a decrease in pressure on the position of equilibrium in step 2. Explain your answer. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………[1]

5 ASRJC JC2 PRELIM 2023 9729/02/H2 [Turn over (c) Sulfur also reacts with chlorine to form S2Cl2. Fig. 1.1 shows one of the constitutional isomers of S2Cl2. S Cl S Cl Fig. 1.1 (i) Define the term constitutional isomer. ……………………………………………………………………………………………… ……………………………………………………………………………………………[1] (ii) Using the isomer of S2Cl2 shown in Fig 1.1, • state the oxidation number of S. • suggest a value for the Cl–S–S bond angle. Explain your answer. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………[3] (iii) Draw the ‘dot-and-cross’ diagram of another isomer of S2Cl2, given that • one of the S atoms has an oxidation number of zero. • the other S atom is the central atom. [1]

6 ASRJC JC2 PRELIM 2023 9729/02/H2 (d) SO3 can react with SC l2 to form liquid SOC l2 and another gas which turns aqueous acidified potassium manganate(VII) from purple to colourless. (i) Write a balanced chemical equation for the reaction between SO3 and SCl2. …………………………………………………………………………………………..[1] (ii) Draw the organic product formed when compound A is reacted with SOCl2. [1] [Total: 19] Compound A organic product SOCl2

7 ASRJC JC2 PRELIM 2023 9729/02/H2 [Turn over BLANK PAGE

8 ASRJC JC2 PRELIM 2023 9729/02/H2 2 (a) Phthalic anhydride is an important industrial chemical for the synthesis of phthalic esters, which are used as plasticisers to soften plastics. Phthalic anhydride Phthalic acid (C8H6O4) The reactivity of phthalic anhydride is similar to that of acyl chloride. Hydrolysis of phthalic anhydride produces phthalic acid, which is an aromatic dicarboxylic acid that can ionise in two stages, each with its associated pKa value as shown in Table 2.1. Table 2.1 C8H6O4 C8H5O4– + H+ pKa1 = 2.89 C8H5O4– C8H4O42– + H+ pKa2 = 5.51 (i) Suggest reagents and conditions for hydrolysis of phthalic anhydride to form phthalic acid. ……………………………………………………………………………………………..[1] (ii) Suggest two reasons why the pKa2 of phthalic acid is higher than its pKa1. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………..[2]

9 ASRJC JC2 PRELIM 2023 9729/02/H2 [Turn over (b) A student pipetted 10 cm 3 of 0.50 mol dm –3 of phthalic acid into a conical fla