2024 CCKSS 4E Prelim SciCH MS

Paper 1 (MCQ)1. C 2. A 3. A 4. C 5. B 6. B 7. D 8. B 9. A 10. D 11. D 12. C 13. B 14. C 15. B 16. C 17. B 18. D 19. A 20. D

Paper 3 - Section A – 55m Q/No. Answer Comments/Instructions/ Suggestions to Markers M 1a Carbon dioxide; [1] 1b acidified potassium manganate(VII); [1] 1c silver chloride; [1] 1d Methane; [1] 2ai [1] 2aii Energy of the reactants is higher than the products showing that energy is transferred /released into the surroundings; [1] 2bi Magnesium oxide and hydrogen gas; [1] 2bii Silver, chromium, beryllium, magnesium; [1] 3ai covalent [1] 3aii -number of atoms -number of bonding electrons -number of non bonding electrons 3pt = 2m 1 to 2 pt = 1m [2] 3bi there are strong electrostatic forces of attraction between the ions; large amount of energy is needed to overcome the forces; [2] 3bii mobile ions/ free moving ions present in molten state only; [1] 4a 78; [1] energy progress of reaction Mg + H2SO4 MgSO4 + H2

Q/No. Answer Comments/Instructions/ Suggestions to Markers M 4b nitrogen and oxygen under high temperatures in the car engines react to form nitrogen monoxide; [1] 4c in large quantities cause death / prevents blood from transporting oxygen / [1] 4d Carbon dioxide is released through combustion of (carbon containing) fuels / respiration / decomposition / decay; Carbon dioxide is taken in through photosynthesis / ocean uptake; If carbon dioxide released is more than carbon dioxide taken in, there will be a net increase in carbon dioxide in the atmosphere / Carbon dioxide released will be balanced by or is equal to the carbon dioxide taken in.; [3] 5(a) G; [1] 5(b) E; [1] 5(c) D; [1] 5(d) F & G; [1] 5(e) H; [1] 6a Drawing – 1m Label – 1m [2] 6b M – CO2 / carbon dioxide N – BaSO4 / barium sulfate O – CuCl2 / copper(II) chloride P – Cu(OH)2 / copper(II) hydroxide Q – AgCl / silver chloride [5] 6c Ba(NO3)2 (aq) + SO42– (aq) BaSO4 (s) + 2NO3– (aq) Ba2+ (aq) + SO42– (aq) BaSO4 (s) 2HNO3 (aq) + CO32– (aq) 2NO3– (aq) + H2O (l) + CO2 (g) 2H+ (aq) + CO32– (aq) H2O (l) + CO2 (g) CuCl2 (aq) + 2AgNO3 (aq) 2AgCl (s) + Cu(NO3)2 (aq) Ag+ (aq) + Cl– (aq) AgCl (s) formula [1] balanced equation [1] state symbols [1] [3] Black solid Colourless solution

Q/No. Answer Comments/Instructions/ Suggestions to Markers M CuCl2 (aq) + 2NaOH (aq) 2NaCl (aq) + Cu(OH)2 (s) Cu2+ (aq) + 2OH– (aq) Cu(OH)2 (s) 7ai CnH2n+1COOH [1] 7aii same general formula / similar chemical properties / shows a gradation in physical property 1pt = 1m, max 2m [2] 7b produce hydrogen ions / H+ in aqueous solution / water [1] 7c ● arrangement: from quite closely packed, disorderly manner ● to far apart, disorderly manner or randomly arranged ● movement: from sliding over each other ● to move randomly at high speed or quickly 4 pt = 3m 2 to 3 pt = 2m 1 pt = 1m [3] 7di Mr of propanoic acid = 12 x 3 + 1 x 6 + 2 x 16 = 74 [1] 7dii Concentration = 125 / 74 = 1.69 [1] 7diii Concentration = 1 / 2 = 0.500 [1] 8a Powdered marble is of smaller particle size; When particle size decreases, exposed surface area increases / surface area: volume ratio increases; Frequency of effective collisions increases; Speed of reaction will increase and affect the results; 2 pt = 1m [2] 8bi At a lower temperature ● reacting particles have lesser kinetic energy / less particles have energy greater than or equal to activation energy ● lower frequency of effective collision ● reaction is slower / graph or gradient is less steep 3pt = 2m 1 or 2 pt = 1m [2] 8bii At a lower concentration ● the same volume of acid used will produce lesser volume of gas ● lesser reacting particles per unit volume ● lower frequency of effective collision ● reaction is slower / graph or gradient is less steep 4 pt = 3m 2 or 3 pt = 2m 1pt = 1m [3] 8ci Mole of CO2 = 100 / 24000 = 1/240 ; Mr of CaCO3 = 40 + 12 + 16 x 3 = 100 Mass of CaCO3 = 1/240 x 100 = 0.417 g ; [2] 8cii Mass of CaCO3 = 0.417 x 2 = 0.834 g ; [1]

Paper 3 - Section B – 10m (2 choose 1 question) Q/No. Answer Comments/Instructions/ Suggestions to Markers M 9(a) Ca: 2,8,8,2; 2 valence electrons hence in Group 2; 4 electron shells hence in Period 4; 3pt = 2m 1 or 2 pt = 1m [2] 9(bi) Hydrogen [1] 9(bii) OH– [1] 9(biii) Add Universal Indicator into the solution; Compare the resulting colour with a pH chart to determine the pH; [2] 9(c) Bubbles of gas observed; Violent reaction with potassium and calcium reacts readily; Potassium floats on water and calcium sinks; A: K – lilac flame seen / catches fire [3] 9(d) Argon has completely filled valence shell and is unreactive [1] 10(ai) Cracking naphtha is essential to match the demand for fractions ; containing smaller molecules from the refinery process; [2] 10(aii) Hydrocarbon X Hydrocarbon Y 1m each [2] 10(aiii) Bromine water / aqueous bromine / bromine solution; X – remains reddish brown; Y – turns colourless; 3pt = 2m 1 or 2 pt = 1m [2] 10(aiv) correct partial drawing with at least 2 carbon [1] two repeating units [1] [2] 10(bi) Polyunsaturated contain hydrocarbon chains with two or more carbon-carbon double bonds in each chain [1] 10(bii) The carbon-carbon double bond gets broken / become single bond / hydrogen are added across the double bond [1] Submitted on: 20 June 2024