2025 AES 5086 5088 Sc(Chem) Prelim P1 P3 MS

ASSUMPTION ENGLISH SCHOOL Secondary 4E / 5N Prelim 2025 Science(Chemistry) 5086/5088 – Marking Scheme Paper 1: (20 marks) Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 C D A A D B A B C A Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 Q19 Q20 B A C D A D D C D C Paper 3 SECTION A: (55 marks) 1 (a) carbon monoxide [1] (b) sulfur dioxide [1] (c) aluminium oxide [1] (d) sulfur [1] (e) calcium hydroxide [1] (f) methane [1] 2 (a)(i) D [1] (a)(ii) E [1] (a)(iii) A [1] (b)(i) B and C [1] (b)(ii) Yes, they have the same electronic configuration / number of electrons. Or Yes, they lose, gain or share the same no. of electrons during reactions. [1] (c) carbon dioxide [1] (d) The gas is a covalent molecule that is held together by weak intermolecular forces of attraction, where little energy is needed to overcome, resulting in a low melting point. Award 1m for every 2 correct points [2] 3 A – mixture, B – compound, C – element, D – compound [4]

4 Cracking decomposition exothermic [3] 5 (a) Movement of particles changes from sliding over one another to moving randomly at high speeds. Arrangement of particles changes from disorderly and quite closely packed to spaced far apart. Award 1m for every 2 correct points [2] (b) Award 1m for shape of graph Award 1m for labelling of temperature and axes [2] (c)(i) Fractional distillation [1] (c)(ii) They are liquids that have different boiling points. [1] 6 (a) W and X show two spots in chromatogram with water as solvent and ethanol as solvent respectively [1] (b) Pencil lead is insoluble in the solvent and does not affect the results. [1] 7 (a) Ions are fixed in position, hence there are no mobile ions to conduct electricity. [1] (b) O2- : 10, 16 Mg2+: 12, 12 Award 1m for every 2 correct answers [2] (c) [2]

8 (a) P: copper(II) oxide / CuO Q: hydrochloric acid / HCl R: copper(II) chloride / CuCl2 S: silver chloride / AgCl T: copper(II) hydroxide / Cu(OH)2 Award 1m for every 1 correct answer [5] (b) Ag+ (aq) + Cl- (aq) → AgCl (s) Accept answer without state symbol [1] 9 (a)(i) Colourless solution turns brown. [1] (a)(ii) Chlorine is more reactive than iodine and is able to displace iodine from potassium iodide. [1] (b)(i) pH 1 / 2 [1] (b)(ii) Bubbles of gas seen. Hydrogen ions are acidic and will react with carbonates to form carbon dioxide gas. [1] [1] 10 (a) Reactivity increases down the group. Melting point decreases down the group. [1] [1] (b)(i) Test: Place a lighted splint in the path of the gas. Observation: Flame extinguishes with a pop sound. [1] (b)(ii) Similarity - Bubbles of gas produced - Temperature of mixture increases (exothermic) Difference - Reaction with potassium is more violent / faster / explosive [2] (c)(i) +3 [1] (c)(ii) CO It gains oxidation state / oxygen atom and is oxidised Or It causes iron(III) oxide to lose oxygen and be reduced. [1] (c)(iii) 20% of 2 kg = 400 g [1] (c)(iv) No. of moles of iron(III) oxide = mass / Mr = 400 / 160 = 2.5 mol No. of moles of CO2 = 7.5 mol Volume of CO2 = 7.5 x 25 = 180 dm3 [1] [1]

Paper 3 SECTION B: (10 marks) 11 (a) No. of moles of Na2CO3 = 7.95/ 106 = 0.075 mol Concentration = 0.075 / (50/1000) = 1.5 mol/dm3 [1] [1] (b) Volume of gas / mass of experimental set up and time [1] (c) (d)(i) (d)(ii) Award 1m for shape of graph and 1m for correct axes. If (b) mentioned mass of experimental set up, then accept graph of mass vs time instead. [2] (e) At a higher concentration, there are more reactant particles per unit volume available for collision. Thus frequency of effective collisions is higher and hence the rate of reaction will be faster, giving a steeper graph. [1] [1] (f) No effect. [1] 12 (a) Ethanoic acid / CH3COOH [1] (b) Name: fermentation Conditions: 37C, absence of oxygen gas [1] [1] (c) Type of reaction: oxidation Observation: purple acidified potassium manganate(VII) turns colourless / pink. [1] [1] (d) Test: Bubble the gases in aqueous bromine solution / Add aqueous bromine to B and D. B: Reddish brown bromine turns colourless D: Reddish brown bromine stays the same. Award 1m for 1-2 correct, 2m for all 3 correct [2] (e) [1]

(f)(i) [1] (f)(ii) Physical Method: Mechanical Recycling – Plastics are sorted, shredded into small pieces before melting and cut into pellets Chemical Method: Cracking – Plastics are broken down under certain conditions into raw materials [1]