2024 CHIJ Sec 4E Chemistry Prelim Answers

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2024 Mark Scheme / P1/8 CHIJ SECONDARY Sec 4 Preliminary Examination 2024 Chemistry 6092 Mark Scheme Updated on 05/09/2024 Paper 1 (40 marks) No Answer No Answer No Answer No Answer 1 D 11 D 21 D 31 C 2 D 12 B 22 B 32 C 3 C 13 B 23 B 33 D 4 A 14 B 24 C 34 D 5 C 15 D 25 A 35 D 6 C 16 D 26 B 36 C 7 B 17 C 27 D 37 B 8 D 18 C 28 B 38 B 9 C 19 A 29 C 39 D 10 B 20 C 30 A 40 D Paper 2 Section A (70 marks) Question Answers Marks Total 1 (a) C 1 5 (b) B 1 (c) C 1 (d) A 1 (e) D and E 1 2 (a) [1]: size [1]: composition 2 8 (b) (i) The iron and carbon atoms are physically combined / not chemically combined together. 1 (ii) Steel has atoms of different sizes that disrupts the regular arrangement of the metal [1] causing the layers of atoms to slide over each other less easily. [1] 2 (c) There are free moving electrons to carry charge. Steel is made up of positive ions in a “sea of mobile(delocalised) electrons” ‘Sea of delocalised ‘electrons move to conduct electricity 1

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2024 Mark Scheme / P2/8 Question Answers Marks Total (d) Chromium is more reactive than iron [1] and corrodes/oxidises in place of iron. [1] 2 3 (a) (i) Energy absorbed = 4C-Cl + 4O-H = 4(340) + 4(460) = 3200 kJ 1 5 (ii) ∆H = energy absorbed + energy released -130 = +3200 – [2C=O + 4H-Cl] -130 = +3200 – [2(805) + 4H-Cl] 4H-Cl = 1720 H-Cl = 430 kJ/mol 1 (b) There is more energy released [1] in forming the C=O and H-Cl bonds / bonds in CO2 and HCl [1] than energy taken in to break the C-Cl and O- H bonds / bonds in CCl4 and H2O. [1] OR Energy released/given out in forming the C=O and H-Cl bonds / bonds in CO 2 and HCl [1] is more[1] than energy taken in /absorbed to break the C-Cl and O-H bonds / bonds in CCl4 and H2O. [1] 3 4 (a) Ammonium chloride: hydrochloric acid; ammonium carbonate/aqueous ammonia [reject: ammonium hydroxide] Calcium sulfate: sulfuric acid [1]: 1-2 correct, [2]: all 3 correct 2 6 (b) An insoluble layer of calcium sulfate forms over the calcium carbonate, preventing further reaction. 1 (c) 3 CaCl2(aq) ∆H

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2024 Mark Scheme / P3/8 Question Answers Marks Total [1/2]: correct shape of each graph [1/2]: correct arrow direction with ∆H label for each graph [1/2]: correct formula and state symbol of each product 5 (a) (i) Zn electrode: Zn → Zn2+ + 2e- [1] Cu electrode: Cu2+ + 2e- → Cu [1] 2 9 (ii) Any 2: • The zinc electrode decreases in size • The copper electrode increases in size/ a reddish-brown solid forms on the copper electrode • The electrolyte/solution changes from blue to colourless 2 (b) Any value b