2025 CHIJ SEC (TP) Chemistry Prelim Paper 1 and Paper 2 MS

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2025 Mark Scheme / P1/10 CHIJ SECONDARY Sec 4 Preliminary Examination 2025 Chemistry 6092 Mark Scheme Updated on 14/09/2025 Total Score = (P1/40×30%) + (P2/80×50%) + (P3/40×20%) Paper 1 (40 marks) No Answer No Answer No Answer No Answer 1 A 11 C 21 C 31 B 2 B 12 A 22 C 32 C 3 B 13 B 23 B 33 C 4 D 14 D 24 A 34 B 5 C 15 B 25 D 35 B 6 D 16 D 26 D 36 B 7 D 17 C 27 D 37 A 8 A 18 A 28 C 38 B 9 C 19 C 29 A 39 B 10 D 20 C 30 C 40 A Abbreviations: ORA: or reverse argument AW: alternate wording ECF: error carried forward (for calculations only)

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2025 Mark Scheme / P2/10 Paper 2 Section A (70 marks) Question Answers Marks Total Comment 1 (a) Zn 1 5 (b) Br 1 (c) Li 1 (d) Ar 1 (e) Ag 1 ZnO is white when hot and yellow when cold, so it only forms 1 coloured compound. 2 (a) The black dye is impure. (no mark) There is more than one component/spot on the chromatogram. 1 6 (b) Boil/freeze the black dye / Determine the boiling point/freezing point of the black dye. If the black dye boils/freezes at a fixed temperature, it is pure. or If the black dye boils/freezes over a range of temperatures, it is not pure. 1 1 Reject methods relating to melting. (c) Dye B is insoluble in the solvent/ethanol. 1 (d) Dye A Distance of A from start line = 2.5 cm Distance of solvent front from start line = 5.5 cm (values must be correct) Rf value = 2.5 / 5.5 = 0.45 OR 0.45 = distance moved by solute ÷ (7 – 1.5) distance moved by solute = 0.45 × 5.5 = 2.475 Position on chromatogram = 2.475 + 1.5 = 3.975 ≈ 4cm 1 1 3 (a) nitrogen = 78% oxygen = 21% 1 7 % sign is not required (b) 32 / 24 = 1.33 g/dm3 1 (c) (i) The total percentage composition of nitrogen and oxygen on Mars is much lower at 2.8% as compared to 99% on Earth / The percentage composition of nitrogen and oxygen on Mars is much lower at 2.6% and 0.3% compared to 78% and 21% on Earth. At high temperatures (in engines of vehicles or in factories or during lightning activity ), nitrogen and oxygen in the air can react together to form nitrogen monoxide , forming more nitrogen oxides on Earth. 1 1

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2025 Mark Scheme / P3/10 Question Answers Marks Total Comment (ii) In step 1, NO increased the rate of breakdown of ozone by providing alternative reaction pathway of lower activation energy; In step 2, the regeneration of NO showed that it remained chemically unchanged at the end of the reaction. 1 1 (d) Mars has a high composition of carbon dioxide which traps heat/causes global warming. 1 4 (a) (i) Y (Anode): 2Cl − → Cl2 + 2e− Z (Cathode):