Pasir Ris 2024 4E Prelim MS

SEC 4 EXPRESS – CHEMISTRY 6092 PRELIM EXAM 2024 - ANSWERS Paper 1 – MCQ 1 D 11 C 21 D 31 D 2 A 12 D 22 A 32 B 3 B 13 C 23 C 33 C 4 D 14 B 24 B 34 B 5 B 15 D 25 B 35 A 6 D 16 A 26 D 36 C 7 C 17 B 27 B 37 A 8 D 18 D 28 D 38 C 9 B 19 B 29 B 39 D 10 A 20 C 30 D 40 D Paper 2 – Section A – Structured Questions No Suggested Answers Marks 1(a) silicon dioxide [1] 1(b) calcium oxide / copper(II) oxide [1] 1(c) zinc oxide [1] (i) 2(a) (ii) B: iron(II) hydroxide / Fe(OH)2 [1] (iii) C: iron(III) hydroxide / Fe(OH)3 [1] (iv) D: ammonia gas / NH3 [1] (v) E: silver chloride / AgCl [1] [4] 2(b) iron(II) chloride / FeCl3 [1] ammonium chloride / NH4Cl [1] iron(II) nitrate / ammonium nitrate also accepted e.c.f. allowed; follow part (a) answer [2] 3(a) (i) covalent bond [1] There is sharing of valence electrons between atoms. [1] wrong choice of terms -0.5 (ii) There are only six valence electrons surrounding aluminium atom. or Aluminium has not achieved stable noble gas configuration /valence shell not fully filled. or aluminium usually loses electrons but shares electrons with hydrogen instead [1] [3]

NOTE: students should use proper terms e.g. loses electrons instead of giving away electrons / gains electrons instead of taking in electrons. 3(b) (i) correct magnesium ion – [1]: 0.5 for charge, 0.5 for electrons correct hydride ion x 2 – [1]: 0.5 for charge, 0.5 for electrons −[0.5] for missing legend students should note that magnesium ion should be drawn between hydride ions since there are two hydride ions. (ii) Magnesium hydride has a giant ionic structure^ while aluminium hydride has a simple covalent structure^. A large amount of energy # is needed to overcome the strong electrostatic forces of attraction between oppositely charged ions*, while only a small amount of energy# is needed to overcome the weak intermolecular forces of attraction between aluminium hydride molecules*. Hence, the melting point of magnesium hydride is so much higher than the melting point of aluminium hydride. Compare type of structures^ – [1] Compare amount of energy# – [1] Compare bonds/forces* – [1] penalised if wrong choice of words e.g. atoms / ions / molecules for the wrong examples. misconception: covalent bonds are weak / weaker than ionic bonds intermolecular forces between aluminium and hydrogen atoms [5] 4(a) Sulfur dioxide [0.5] is released into the atmosphere, it will be oxidised by the atmospheric oxygen and dissolved into rainwater to form acid rain [0.5]. Acid rain will corrode limestone buildings and metal infrastructures / destroy crops and vegetation / kill lakes [1]. (mentions at least 2 effects) students confused between silicon dioxide and sulfur dioxide they tend to ignore environmental issue and gave health issues instead. [2] 4(b) (i) aqueous copper(II) sulfate / chloride / nitrate [1] copper(II) hydroxide is rejected since it is insolub