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 between 1.20 to 1.40V [1] (actual: 1.36V) The difference in reactivity between zinc and silver is greater than the difference in reactivity between zinc and copper. [1] 2 (c) Volume at O should be 8cm3 [1] Every 2 points is 1 mark: P: 2H+ + 2e- → H2 Q: 4OH- → O2 + 2H2O + 4e- [1] From the equations for every 4 moles of electrons that pass through electrolysis, 2 moles of hydrogen are produced at the cathode and 1 mole of oxygen is produced at the anode. [1] OR Overall reaction is 4OH- + 4H+ →2 H2 + O2 + 2H2O Mole ratio of H2:O2 is 2:1, the volume ratio of H2:O2 is also 2:1 [1] 3 NH4Cl(aq) ∆H

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2024 Mark Scheme / P4/8 Answers Marks Total 6 (a) Volume of CO2 = 42 cm3 1 11 (b) no. of moles of CO2 = 42/1000 ÷ 24 = 0.00175 mol [1] no. of moles of HCl = 0.00175 × 2 = 0.0035 mol volume of HCl = 0.0035 ÷ 0.10 = 0.035 dm3 = 35 cm3 [1] 2 © (i) 1 (ii) MgCO3 + 2CH3COOH → (CH3COO)2Mg + H2O + CO2 1 (d) In experiment 3, the higher temperature leads to the particles possessing more kinetic energy / move faster [1] frequency of collisions increases. Further more particles possess energy greater than or equal to the activation energy. [1] The frequency of effective collisions increases, [1] resulting in a faster rate(or an increase in rate) of reaction. [1] 4 (d) Ethanoic acid is a weak acid, which only partially ionises in water, producing a low concentration of hydrogen ions than hydrochloric acid. [1] Hydrochloric acid is a strong acid which ionises completely in water to produce a high concentration of hydrogen ions[1] 2

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2024 Mark Scheme / P5/8 Answers Marks Total 7 (a) CO: binds to haemoglobin in blood, preventing flow of oxygen around the body, leading to breathing difficulties ( or loss of consciousness and even death [1] OR CO binds irreversibly with the haemogobin in red blood cells. This lowers the ability of the hemoglobin to transport oxygen to the rest of the body. This can result in loss of consciouness and death. NO2: cause acid rain, which can corrode limestone buildings/kill aquatic life/kill plants [1] 2 8 (b) CO: Lean burn engines have more air, so the petrol tends to undergo complete combustion to form CO2 instead of CO / less likely to undergo incomplete combustion to form CO [1] NO2: Lean burn engines have lower operating temperature, so nitrogen and oxygen in the air are less likely to react to form oxides of nitrogen [1] OR NO2 is formed when nitrogen reacts with oxygen at high temperature. 2 (c) (i) Catalysts provide an alternate pathway of lower activation energy allowing the reaction to proceed faster. 1 (ii) CO is oxidised as the oxidation state of C increases from +2 in CO to +4 in CO2 [1] NO2 is reduced as the oxidation state of N decreases from +4 in NO2 to 0 in N2 [1] OR Carbon in CO is oxidised as the oxidation state of C increases from +2 in CO to +4 in CO2 [1] Nitrogen in NO2 is reduced as the oxidation state of N decreases from +4 in NO2 to 0 in N2 [1] 2 (iii) The catalytic converter still produces carbon dioxide, which causes global warming. 1

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2024 Mark Scheme / P6/8 8 (a) Ethyl butanoate 1 8 (b) Full structural formula of alcohol: [1] Full structural formula of carboxylic acid: [1] 2 (c) Test: Add reactive metal/carbonate [1] Outcome: If effervescence is observed, it is the acid. If there is no visible change, it is the alcohol. [1] OR Test: Add acidified KMnO4 [1] Outcome: If it turns from purple to colourless, it is the alcohol. If there is no visible change, it is the acid. [1] 2 (d) (i) C [1] Ethyl butanoate is insoluble in water, while alcohols and carboxylic acids are soluble in water. [1] 2 (ii) If the ethyl butanoate freezes or boils at a fixed temperature, it is pure. 1 9 (a) 12C and 13C both have 6 protons (and 6 electrons), [1] but 12C has 6 neutrons while 13C has 7 neutrons. [1] 2 10 (b) There are 2 carbon atoms of the same ‘type’ d compared to carbon atoms a, b and c, which only have 1 each. [1] Because both carbon atoms d are attached to a –C3H7 alkyl group. [1] 2 (c) The closer the carbon atom is to the end of the carbon chain, the lower its position on the arbitrary scale. [1] The terminal carbon, Ca, has the lowest value at 14 for isomer 1 and 12 for isomer 2. [1] The next carbon atom, Cb, has the second lowest value at 23 for isomer 1 and 25 for isomer 2 / the carbon atom in the centre of each molecule, Cc, has the highest value at 34 for isomer 1 and 32 for isomer 2. [1] OR 3

CHIJ SECONDARY Sec 4 Chemistry Prelim Exam 6092_2024 Mark Scheme / P7/8 The more alkyl groups attached to the carbo