2023_ASRJC_H2_Chem_Prelim_P2_MS

ASRJC JC2 PRELIM 2023 9729/02/H2 [Turn over Anderson Serangoon Junior College 2023 JC2 H2 Chemistry Preliminary Examination Paper 2 Suggested Solutions 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] 563.23 10 250 10 0.01948.31 500n −  ==  Mr = 3.30 0.0194 = 170.1 [1] SiCl4 [1] matches the Mr from the table. 1 (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] Period 3 chloride NaCl AlCl3 SiCl4 PCl5 Bonding [1] I C C C Structure [1] G S S S pH of aqueous solution [1] 7 3 1 or 2 1 or 2

2 ASRJC JC2 PRELIM 2023 9729/02/H2 (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] Al Al Cl Cl Cl Cl Cl Cl [1] Trigonal planar about Al to tetrahedral about Al [1] (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] Structure: simple / molecular, because it has a low melting / boiling point Bonding: covalent, because it undergoes complete hydrolysis. [1] for correct structure and bonding Explanation: it has a low melting point (as it is a liquid) and it undergoes complete hydrolysis (reacts vigorously with water). [1] for correct explanations on m.p. and hydrolysis SCl2 is formed when sulfur, S 8, reacts with an excess of chlorine in a s