XMS SEC 3 WA2 2023 MS

1 Sec 3E Chemistry 6092 / Year 2023 / Term 2 WA2 Mark Scheme SECTION A [5 marks] Question 1 2 3 4 5 Answer C B A D A SECTION B [10 marks] 6 (a) (1), 12, 8 1 (b) (1), 5, 3, 4 1 (c) 2, 3, 6, (1) 1 [total 3 marks] 7 (a) Metallic structure, [1] lattice of positive ions [ ½ ] in a sea of delocalized electrons. [ ½ ] 2 (b) (i) Sc2(SO4)3 1 (i) Sc(OH)3 1 [total 4 marks] 8 (a) Any one of the following: • High melting point • Insoluble in water (but soluble in organic solvent) • Conducts electricity • Brittle / slippery 1 (b) compare – both buckyball and graphite have 1 carbon atom covalently bonded to 3 other carbon atoms, with 1 (unbonded) electron, delocalized, free-moving / mobile, able to conduct electricity. prediction – buckyball can conduct electricity 1 1 [total 3 marks] SECTION C [20 marks] 9 9 (a) element to chlorine ratio increases from 1:1 (in NaCl) to 1:4 (in SiCl4), then decreases to 1:1 (in S2Cl2 and Cl2). 1 1 (b) Data from table 9.1 agrees with student 2, disagrees with student 1. chlorides that hydrolyse all contain covalent bonding / chlorides that dissolves all contain ionic bonding Use of aluminium chloride to illustrate: although aluminium is a metal, aluminium chloride (AlCl3) is a covalent chloride, and aluminium chloride hydrolyses (as per covalent chlorides) but not dissolves. 1 1 1 (c) Argon has stable electronic configuration (full valence shell) and does not react and form chloride. 1

2 REJECT: Argon is a noble gas, hence unstable / inert. (d) Cl2 (g) + H2O (l) → HClO (aq) + HCl (aq) [1] correct state symbols [1] correctly balanced 2 (e) (i) [1] single covalent bond Cl-Cl [1] octet for all atoms 2 (ii) × electron of chlorine • electron of sulfur [1] single covalent bond S-Cl, S-S [1] octet for all atoms Allow max [1] if incorrect symbols used. 2 [total: 12 marks] 10 (a) [1] correct ratio of 2 Li+ to 1 O2- [1] correct ion with charge for both Li+ and O2- 2 (b) Li2O : solid CH4 : gas 1 1 (c) Li2O – giant ionic lattice As a solid (at r.t.p.), ions are held in fixed positions, unable to move freely to conduct electricity. CH4 – simple molecules As a gas (at r.t.p.), weak intermolecular forces of attraction (Van der Waals’ forces); which require little (heat) energy to overcome, hence low mp, bp. 1 1 1 1 [total: 8 marks]  End of answers and marking scheme  2 S S Cl Cl