AMKSS Prelim P4 ans

4NA 2025 Science Chemistry Prelim MS Paper 4 Qn Answer Mark 1 (a) atom nucleon number number of protons number of neutrons number of electrons oxygen- 17 17 8 9 8 oxygen- 18 18 8 10 8 3 correct- 1m All correct -2m (b) (i) Source: Volcanoes/ combustion fossil fuels Effect: irritates eyes and lung/ causes breathing difficulties/ dissolves in rainwater to form acid rain which corrode metals, buildings and harm aquatic living organisms. (anyone answer) 1 1 (ii) test: bubble gas into limewater Observation: white precipitate formed in limewater 1 1 (iii) Correct no. of electrons – 1m Correct sharing of and ratio of atoms – 1m 8 m 2 (a) All these elements have the same number of 7 electrons in their outer shell/valence shell. 1 (b) 1. colour intensity increases 2. melting and boiling point increases (any one) A: Colour gets darker 1 (c) Chlorine is more reactive than iodine [1] When chlorine comes into contact with potassium iodide, chlorine displaced iodine from potassium iodide to form brown iodine solution.[1] 2 (d) arrangement: closely packed and disorderly arranged movement: particles slide past each other. 1 1

4NA 2025 Science Chemistry Prelim MS 6 m Qn Answer Mark 3 (a)(i) There is presence of C=C / carbon-carbon double bond 1 (a) (ii) Observations with margarine: aqueous bromine remains red-brown. Observation with vegetable oil: aqueous bromine turns from red-brown solution to colourless/ decolourise. 1 1 (b) (i) C2H4 + Cl2 → C2H4Cl2 1 H H l l H C C H l l Cl Cl 1 (ii) Mr of C6H12 = 6x12 +12 x 1 =84 Mass = 15 x 84 = 1260 g / 1.26 kg 1 1 (iii) Poly(hexene) R: wrong spelling 1 8 m 4 (a)(i) Oxygen in air is used up during reaction with iron. 1 (ii) Painting/ greasing/ cover with plastic [ any possible ans] 1 (iii) Fe + H2SO4 → FeSO4 + H2 1 (b)(i) most reactive R Q least reactive S 1 (ii) Correct no. of electrons – 1m Correct charges and ratio – 1m Magnesium oxide has a giant crystal lattice structure. There are strong electrostatic forces of attraction between the opposite charged ions[1]. A large amount of energy is required to overcome these forces of attraction[1], hence it has high melting point. 2 2- O 2+ Mg

4NA 2025 Science Chemistry Prelim MS 8 m Qn Answer Mark 5 (a) experiment with zinc mass of zinc/ g highest temperature recorded/ ⁰C temperature rise/ ⁰C 0.0 25.0 0.0 0.2 27.5 2.5 0.4 29.9 4.9 0.6 32.4 7.4 0.8 33.0 8.0 1.0 33.0 8.0 1.2 33.0 8.0 All correct - 1m (i) correct plotting, 7 points 1 (ii) Two intersecting straight lines 1

4NA 2025 Science Chemistry Prelim MS c(i) 0.33 g (value form the graph) 1 c(ii) 0.65 g (value form the graph) 1 (d) Zn + CuSO4 → ZnSO4 + Cu 1 (e) No change/ no rise in temperature / temperature reading remains at 25 ⁰C Silver metal is less reactive than copper metal. Silver cannot displace copper from its salt solution. 1 1 8 m