RI 2024 The Periodic Table 1 Tutorial Discussion Question answers

-1- Raffles Institution Year 5 H2 Chemistry 2024 Tutorial 12 – The Periodic Table 1 Suggested Answers to Practice Questions 8 Answer: D Strategy 1. Observe x-axis (electrical conductivity) The metals (Na, Mg and A l) have high electrical conductivity (lie to the right of the axis) and increases from Na to Mg to Al i.e. Al would be most far right. ⇒ Reject A and B. 2. Observe y-axis (1st ionisation energy) Using data from data booklet, P has the highest first IE ⇒ Reject C. 9 Answer: D A Cl2 molecule has less electrons than P 4 molecule. Hence C l2 has weaker instantaneous dipole-induced dipole interactions and has a lower melting point. B Na has a lower melting point than Mg due to weaker metallic bonding in Na. C S8 molecule has more electrons than P 4 molecule. Hence S 8 has stronger instantaneous dipole-induced dipole interactions and has a higher melting point. D S8 molecule has more electrons than P 4 molecule. Hence S 8 has stronger instantaneous dipole-induced dipole interactions and has a higher melting point. SiO 2 is also the only insoluble oxide amongst the three elements. 10 Answer: A W is Silicon. X is Aluminium. Y is either Phosphorus or Sulfur. Z is Sodium. 11 (a) Molecular formula of the vapour: Al2Cl6 Note: 2 molecules of AlCl3 dimerise to form Al2Cl6 which is more stable (as Al is electron deficient in AlCl3). (b) When only a few drops of water are added to the solid, steamy white fumes of HCl are evolved and together with the formation of Al(OH)3, a white solid, which is insoluble in water. Al2Cl6(s) + 6H2O(l) → 2Al(OH)3(s) + 6HCl(g) white solid steamy white fumes OR AlCl3(s) + 3H2O(l) → Al(OH)3(s) + 3HCl(g) white solid steamy white fumes When a large amount of water is added to the solid, [Al(H2O)6]3+(aq) is formed. AlCl3(s) + 6H2O(l) → [Al(H2O)6]3+(aq) + 3Cl–(aq) colourless solution

-2- [Al(H2O)6]3+(aq) undergoes hydrolysis as shown below. [Al(H2O)6]3+(aq) ⇌ [Al(H2O)5(OH)]2+(aq) + H+(aq) OR [Al(H2O)6]3+(aq) + H2O(l) ⇌ [Al(H2O)5(OH)]2+(aq) + H3O+(aq) Acidic Al3+ ions, with high charge density and hence high polarising power, are able to distort the electron cloud of the water molecules, weakening the O–H bond. As a result, the O–H bond undergoes heterolytic fission readily to release H+. Note: yellow–white solid can be denoted by AlCl3 or Al2Cl6 (c) Na2O(s) + H2O(l) → 2NaOH(aq) Na2O(s) dissolves to produce NaOH(aq). The litmus solution turns from purple to blue due to the presence of OH– ions. (d) (i) (d) (ii) Mg3N2(s) + 6H2O(l) → 3Mg(OH)2(s) + 2NH3(g) . . ( . ) ( . ) 32 20Amount of Mg N 0 01982 mol 3 24 3 2 14 0 == + ..2Amount of Mg(OH) 3 0 01982 0 05946 mol=  = . ( . ( . . )) .2Mass of Mg(OH) 0 05946 24 3 2 16 0 1