AES 4NA Science Chemistry ANSWER KEY

ASSUMPTION ENGLISH SCHOOL N Level PRELIMINARY EXAMINATION 2023 SCIENCE (CHEMISTRY) Paper 3: 20 m 1 2 3 4 5 6 7 8 9 10 B C B B C D C C C B 11 12 13 14 15 16 17 18 19 20 C B A C D D D B C A Paper 4 – Section A: 14 m 1 (a) Ensure smooth boiling. [1] (b) Methanol. It has a lower boiling point and will boil first. [1] (c) Arrangement: Far apart from one another in a disorderly manner. Movement: Moves fast in any direction / moves fast and freely. [1] [1] 2 (a) Yellow [1] (b) H+ (aq) + OH- (aq) → H2O (l) [1] (c) Potassium carbonate or Potassium oxide Do not accept Potassium metal as it is too reactive. [1] 3 (a) Alloy (Can accept Steel) [1] (b) The material contains atoms of different sizes, disrupting the orderly arrangement of pure iron. When a force is applied, the layers of atoms do not slide over one another so easily, making it a stronger material. Award 1m for every 2 correct points. [1] [1] (c) Element: oxygen Compound: water [1] 4 (a) Test: Place a lighted splint in the path of the gas Observation: Flame extinguishes with a pop sound. [1] (b) metal letter P, Q, R or S magnesium S zinc P iron R copper Q Award 1m for every 2 correct answers. [2]

Paper 4 – Section B: 16 m 5 (a) sodium atom chlorine atom hydrogen atom number of protons 11 17 1 number of electrons 11 17 1 arrangement of electrons 2.8.1 2, 8, 7 1 Award 1m for every 2 correct answers [2] (b) Proton: In the nucleus Electron: On electron shell / outside the nucleus [1] (c) 2 Na (s) + Cl2 (g) → 2 NaCl (s) Award 1m for balanced chemical equation and 1m for state symbol [2] (d) When dissolved in water, mobile ions are available to act as charge carriers to conduct electricity. [1] (e) Award 1m for bonding electrons Award 1m for non-bonding electrons [2] 6 (a) (i) [2]

Award 1m for correct plotted points (allow for 1 incorrect / missing plotted points)(point for t=3 min should not be plotted, would be considered as incorrect point if plotted) and 1m for smooth curve drawn (ii) Follow reading on graph [1] (iii) Test: Bubble gas produced in limewater Observation: white ppt formed. [1] (b) (i) No of moles = mass / Mr Mr = mass / no. of moles Mr = 87 / 0.75 = 116 [1] (ii) 116 – 12 – 3(16) = 56 X is iron [1] (c) Filter the mixture to remove excess metal carbonate. Heat the filtrate till saturated and allow mixture to cool. Wash the crystals with distilled water and dry with filter paper. 5 points – 2 m 3-4 points – 1m [2] 7 (a) (i) Cracking [1] (ii) C4H10 [1] (iii) Fractional Distillation [1] (b) (i) Reddish brown bromine solution turns colourless. [1] (ii) Addition / hydrogenation [1] (iii) [1] (iv) 2 C3H6 + 9 O2 → 6 CO2 + 6 H2O Award 1m for correct formula Award 1m for balanced equation [2]