CHIJ 2025 Sec 4E5N Prelim Sc(Chem) P1 & P3 MS

1 2025 Science Chemistry Mark Scheme Paper 1: Multiple Choice Items (20 marks) 1 2 3 4 5 6 7 8 9 10 B C C B D D B A B C 11 12 13 14 15 16 17 18 19 20 D D A D C B B D C C Paper 3: Section A (55 marks) Qn No Answers Marks Total 1 (a)(i) N and F 1 5 (ii) Ar 1 (b)(i) 40 1 (ii) 28 1 (iii) 3.5 / 70 = 0.05 mol 1 2 Calcium hydroxide / calcium oxide / slaked lime / quicklime; Hydrogen / nickel catalyst Any ammonium salt; Potassium iodide; Acidified potassium manganate(VII); 5 5 3 (a) 2Cu + O2 → 2CuO [1] correct balanced equation 1 6 (b) Exothermic (no marks) Copper glows brightly, energy is given out. 1 (c) Basic oxide (no marks) Copper is a metal; metal oxides are (generally) basic. 1 (d) Arrangement: Very closely packed, orderly arrangement [1] Movement: Vibrate about their fixed positions [1] 2 (e) Ratio of Cu:Zn must be 3:2 1 4 (a) Any one: • Malleable • Ductile • Conduct electricity • Good conductor of heat 1 7 (b) • more reactive metals forms more stable compound / more reactive metals form stronger bonds to other elements Examples: Any two • Calcium is very reactive and requires electrolysis, while • Iron moderately reactive can be extracted by reduction iron ore with carbon. • Gold is so unreactive it occurs naturally as the element 3

2 Qn No Answers Marks Total (c)(i) To remove (dissolved) oxygen from water. 1 (ii) Nail in Experiment A will rust. [1] Oxygen and water are present in experiment A. [1] 2 5 (a)(i) H+(aq) + OH-(aq) → H2O(l) 1 6 (ii) 1. Number of mole of fumaric acid = 20/1000 x 0.2 = 0.004 mol [1] 2. Number of moles of sodium hydroxide = 0.004 x 2 = 0.008 [1] 3. Volume of sodium hydroxide = 0.008 / 0.5 =0.016 dm3 = 16 cm3 [1] 3 (b) Test: add aqueous bromine (no marks) Observation with fumaric acid: brown bromine decolouries / turns colourless [1] Observation with ethanoic acid: remain browns [1] / No observable change (only if “brown” was mentioned in previous point) 2 6 (a)(i) Silver ion (no marks) Silver ion gains electrons / Cause bromide ions to lose electrons. 1 5 (ii) Section covered will remain white/cream [1]; section not covered will turn black [1] 2 (b)(i) 1 (ii) CH4 + 2Cl2 → CH2Cl2 + 2HCl 1 7 (a) P: aluminium nitrate / Al(NO3)3 Q: ammonia / NH3 R: aqueous ammonia / Ammonia water S: aluminium hydroxide / Al(OH)3 T: Sulfuric acid / H2SO4 5 7 (b) Al3+(aq) + 3OH−(aq) → Al(OH)3(s) [1] correct balanced equation [1] correct state symbols 2 8 (a)(i) Draw a thermometer (bulb beside the side arm) + Label 1 7 (ii) Boiling points of butanol and pentanol are above 100 C, the boiling point of water. [1] 1 (b) Propanoic acid [1]; [1] 2 (ci) 37 C (no marks) At 100 C, enzymes in yeast are denatured [1] 1

3 Qn No Answers Marks Total (cii) When plant grows, it takes in carbon dioxide (during photosynthesis), [1] which offsets the carbon dioxide produced when bioethanol is burnt. [1] 2 9 (a) Metal 1 is a unreactive metal, so no reaction, and no mass loss. [1] Metal 4 is a reactive metal and reacts with acid, releasing more hydrogen gas, causing a greater mass loss. [1] 2 7 (b) Rate of reaction will be slower. [1] Since lumps of the metal were used, the particle size increased leading to the decrease in the surface area to react with the acid. [1] Decrease in surface area decreases the frequency of effective collisions. [1] 3 (c) Curve that is below curve of metal 4 [1] Curve that ends at 0.5 [1] 2 Section B Qn No Answers Marks Total 10 (a) O C O [1] Correct number of shared electrons [1] correct number of electrons for carbon and oxygen atoms. 2 10 (b)(i) Natural activity: respiration / decomposition of plants and animals [1] Human activity: combustion of carbon containing fuel. [1] 2 (ii) Global warming 1 (c) Green to yellow Reject green to orange 1 (d)(i) MgO + H2CO3 → MgCO3 + H2O 1 (ii) Any one: • Reaction with carbonic acid will be slower than hydrochloric acid. • Reaction with carbonic acid will produce a precipitate. 1 (e) Carbon dioxide is a simple covalent molecule/has simple molecular structure with no mobile electrons/ions to act as charge carriers. [1] Carbonic acid is an acid with the presence of H+ ions in an aqueous solution. The mobile ions can act as charge carriers. [1] 2

4 Qn No Answers Marks Total Comments 11 (a)(i) Alkali metal 1 10 (ii) Potassium (is very reactive), reacts readily with oxygen in the air to form an oxide layer. 1 (iii) Group 1 metals lose electron readily to form ions. (Reducing agents oxidise easily) 1 (b)(i) Carbon dioxide 1 (ii) The more reactive a metal, the more stable the metal carbonate. 1 (iii) Between 380 to 600. [1] Magnesium is between calcium and zinc in the reactivity series. [1] 2 (c) 3