SJI 2022 Y4 Prelim Chemistry 6092 P1 P2 AS

1 St. Joseph’s Institution 2022 Year 4 OP Preliminary Exam Answer Scheme Paper 1 1 2 3 4 5 6 7 8 9 10 B D B C C C C D B B 11 12 13 14 15 16 17 18 19 20 C D C A A C C B A D 21 22 23 24 25 26 27 28 29 30 D A C D A B B C B B 31 32 33 34 35 36 37 38 39 40 A B A A D A A B B C Paper 2 Section A Qn Suggested answers Mark A1a W: iron / Fe X: zinc sulfate / ZnSO4 Y: barium sulfate / BaSO4 1 1 1 A1b Lighted splint extinguishes with a pop sound. 1 TOTAL 4 A2ai The rate of reaction increases. When temperature increases, the reacting particles have higher kinetic energy, move faster and collide more often. More particles have energy equal to or higher than the activation energy. Thus, the frequency of effective collisions between reacting particles increases. [every 2 points – 1m] 2 A2aii No. Increasing the pressure has no effect on liquids as the particles in liquids are closely packed. 1 A2bi No. of moles of Si2OCl6 = 1 / 285 = 0.0035088 mol No. of moles of Cl- ions = 0.0035088 x 6 = 0.021053 = 0.0211 mol (to 3 s.f.) 1 A2bii No. of moles of Si3O2Cl8 = 1 / 400 = 0.00250 mol No. of moles of Cl- ions = 0.00250 x 8 = 0.0200 mol 1 A2ci Ag+ + Cl- → AgCl 1 A2cii No. of moles of AgCl = 3.03 / 143.5 = 0.0211 mol (to 3 s.f.) Since 1 mole of AgCl forms 1 mole of C l- ions, the oxochloride is Si2OCl6 since the number of moles of Cl- ions are the same at 0.0211 mol. 1 1 TOTAL 8

2 Qn Suggested answers Mark A3ai Nitrogen in the air reacts with oxygen in the air at high temperatures to form nitrogen dioxide gas. 1 A3aii Nitrogen dioxide reacts with oxygen and moisture in the air to form nitric acid. The nitric acid dissolves in rainwater to form acid rain, which falls to the soil. The nitrate ions are formed from the dissociation of nitric acid, causing the soil to have a high nitrate content. 1 1 A3aiii CaCO3 + 2HNO3 → Ca(NO3)2 + H2O + CO2 1 A3bi Carbon dioxide is a greenhouse gas which traps excess heat, causing global warming. Global warming causes ice bergs at the poles to melt, sea levels to rise and leading to floods in lowlands / causes droughts and crop yield to decrease (or any other possible answer). 1 1 A3bii More people should take public transport instead of driving personal cars to decrease carbon dioxide emissions. This is because each car generates much more carbon dioxide than the bus, i.e. 5750 kg of carbon dioxide per year as compared to 3200 kg of carbon dioxide per year. 1 1 A3ci 450 °C, 250 atm and finely divided iron catalyst 1 A3cii The reaction between nitrogen and hydrogen is reversible. 1 TOTAL 10 A4a The oxidation state of sulfur increases from -2 in ZnS to +4 in SO2. ZnS has been oxidised / This is oxidation. The oxidation state of oxygen decreases from 0 in O2 to -2 in ZnO. O2 has been reduced / This is reduction. Since oxidation and reduction occurs simultaneously, this is a redox r