2024 Prelims DHS H2 Chem P1 (Ans)

2024 Y6 Preliminary Examination H2 Chemistry 9729 Paper 1 Suggested Solutions © DHS Chemistry Unit Page 1 of 5 Answer Key 1 2 3 4 5 6 7 8 9 10 B D B D B A D C B A 11 12 13 14 15 16 17 18 19 20 C C A D A B D D A C 21 22 23 24 25 26 27 28 29 30 A D C C C B C A B D 1 B P: [Ne]3s23p3 No. of unpaired electrons = 3  1 Ti: [Ar]3d24s2 Ti2+: [Ar]3d2 No. of unpaired electrons = 2  2 V: [Ar]3d34s2 V2+: [Ar]3d3 No. of unpaired electrons = 3  3 Cr: [Ar]3d54s1 Cr3+: [Ar]3d3 No. of unpaired electrons = 3 2 D H1 = 2nd IE of Si = +1580 kJ mol−1 H2 = 2nd IE of Al = +1820 kJ mol−1 H3 = sum of 1st & 2nd IE of Si = 786 + 1580 = +2366 kJ mol−1 order of decreasing enthalpy change: H3 > H2 > H1 3 B 2H2S + 3O2 → 2SO2 + 2H2O CS2 + 3O2 → CO2 + 2SO2 Hence, SO2 : CO2 will be 4 : 1.  Options A & C are incorrect. Both CO 2 and CS 2 are linear around the central C atom so both are non-polar molecules. CS2 has a larger, more polarisable electron cloud than CO2 so CS2 has stronger instantaneous dipole- induced dipole interactions between molecules. The more significant intermolecular forces result in greater deviation of CS2 from ideal behaviour. 4 D  A magnitude of lattice energy  | q+× q- r++ r- | This is a true statement (Ca2+; 0.099 nm, Na+; 0.095 nm). but a larger cationic radius leads to a less exothermic lattice energy so this does not explain the higher melting point of CaO.  B This is a true statement as Ca2+ has a higher charge than Na+ but their ionic radii are similar (Ca2+; 0.099 nm, Na+; 0.095 nm). However, magnitude of lattice energy  | q+× q- r++ r- | so charge density  q r of the cation alone is not representative of the lattice energy of the compound.  C This is a true statement: sum of ionic radii CaO NaF 0.099 + 0.140 = 0.239 nm 0.095 + 0.136 = 0.231 nm However, a larger sum of ionic radii leads to a less exothermic lattice energy so this does not explain the higher melting point of CaO.  D This is a true statement and the magnitude of lattice energy is larger when the magnitude of ionic charges are larger. 5 B molecule structure shape polarity NCl3 N Cl Cl Cl trigonal pyramidal polar HCN H−C≡N linear polar BeCl2 Cl−Be−Cl linear non-polar SOCl2 S Cl Cl O trigonal pyramidal polar Hence, NCl3 and SOCl2 are polar and have the same shape.

Dunman High School 2024 Y6 Preliminary Examination – H2 Chemistry 9729/01 Solutions © DHS Chemistry Unit Page 2 of 5 6 A Solid X is Na2O which is soluble in water to form the colourless solution of NaOH(aq). On adding CuSO 4(s) to NaOH(aq), pale blue ppt of Cu(OH)2 is formed. Na2O(s) is also soluble in NaOH(aq) as it readily dissolves in water. Solid Y is insoluble in water and could be either Al2O3(s) or SiO 2(s). Since Y is soluble in dilute NaOH(aq), Y is Al2O3(s) which is amphoteric.