MSHS 2024 Chem Prelim MS

1 Secondary Four Chemistry Preliminary Examination 2024 Mark Scheme Paper 1 1 2 3 4 5 6 7 8 9 10 B B D B C C D C C C 11 12 13 14 15 16 17 18 19 20 B B D A D B D D A D 21 22 23 24 25 26 27 28 29 30 C C B A C C D C B B 31 32 33 34 35 36 37 38 39 40 C A C C D C C C A D Paper 2 Section A Qn No. Answer Mark 1a A 1 b D (Accept E: GeCl4 bp: 86.5oC ) 1 c B 1 d C 1 e G 1 Total 5 2a Water vapour produced escaped from the tube OR Water was removed through evaporation. 1 b To ensure that reaction is complete/ no more water (vapour) was produced. 1 c Energy taken in = (2.00 ÷ 238)× 88.1 = 0.740336134 kJ = 0.740 kJ 1 1 d Endothermic/thermal decomposition 1 Total 5

2 Qn No. Answer Mark 3a half equation(s) in each beaker Difference stated In beaker A, the anode would decrease in size /becomes smaller as copper is a reactive electrode and dissolves to form copper(II) ions. Cu(s) → Cu2+ (aq) + 2e In beaker B, there is no change in size for anode. OH - ions are preferentially discharged to form oxygen gas. 4OH- (aq) → 2H2O(l) + O2(g) + 4e- OR There is no effervescence in beaker A as copper is a reactive electrode and dissolves to form copper(II) ions. Cu(s) → Cu2+ (aq) + 2e In beaker B, there is effervescence observed at the anode. OH- ions are preferentially discharged to form oxygen gas. 4OH- (aq) → 2H2O(l) + O2(g) + 4e 1 1 bi Number of moles of electrons = 289500 ÷ 96500 = 3 moles 1 ii Cu2+ (aq) + 2e → Cu (s) No of moles of electrons = 3 moles No of moles of Cu= 1.5 moles Mass of Cu produced in both beakers = 1.5 x 64 g/mol = 96g 1 1 d Universal Indicator will turn from green to violet. Hydrogen ions are preferentially discharged to form hydrogen gas, concentration of OH- more than that of H+, solution becomes alkaline/pH of solution increases. 1 1 Total 7 4a Carbon monoxide produced/chlorine used is toxic/poisonous. 1 b Argon is unreactive/inert. It prevents oxygen/water vapour in the air from reacting with sodium used /titanium produced. 1 1 c Titanium chloride is a m etal chloride which is usually an ionic compound. Ionic compounds have high melting points and are solids at room temperature. 1 1

3 Qn No. Answer Mark d TiCl4 + 4 Na Ti + 4 NaCl From eqn, 1 mol TiCl4 reacts with 4 mol Na 190 g TiCl4 reacts with 92 g Na 190 kg TiCl4 reacts with 92 kg Na 40 kg TiCl4 reacts with (40÷190) x 92 kg = 19.4 kg Na TiCl4 is the limiting reactant since 40 kg of TiCl4 reacts completely with 19.4 kg of Na but 20 kg of Na is available. 1 1 1 e Actual mass = (92.3 ÷ 100) × 13.5 kg = 12.5 kg 1 Total 9 5a Magnesium (most reactive), chromium, iron, nickel (least re