SSS Chem 5105, 5107 Prelim 2021 ANS Final

Singapore Sports School Sc5105, Sc5107 Science(Chemistry) Mark Scheme Answers to Paper 3 1 B 11 B 2 C 12 A 3 D 13 D 4 A 14 C 5 D 15 D 6 B 16 D 7 C 17 A 8 C 18 B 9 A 19 A 10 B 20 C Answers to Paper 4 1k (a) A substance that cannot be broken down into simpler substances / A substance that consists of only 1 type of atoms; [1] (b) (i)a 444°C [1] (ii)u A and B [1] (iii)u Closely-packed sulfur particles absorb heat energy; Particles move faster until the attractive forces of attraction between them break; Particles move out of fixed position and move about randomly within the liquid; [2] [Total: 5]

2a (a) A [1] (b) B [1] (c) D [1] (d) E [1] (e) C [1] [Total: 5] 3 (a)a Covalent structure / Sharing of electrons [1m]; Correct number of electrons [1m]; [2] (b)u Substance X has strong electrostatic force of attraction / ionic bonds between ions; Require large amount of energy to break; Much less energy needed to break weak intermolecular forces of attraction between molecules of Y; [2] [Total: 4]

Section B 4 (a) (i)k 1. Limestone / calcium carbonate 2. Haematite / iron ore 3. Coke / carbon [2] (ii)a 1. Carbon dioxide present 2. An acidic gas present [2] (b) (i)a L, G, H, K (every 2 correct answers 1m) [2] (ii)u Copper / silver [1] (iii)u hydrogen [1] [Total: 8] 5 (a)u No more bubbles were seen / there was solid MgCO3 left; [1] (b)a Magnesium carbonate; [1] (c)a Filtration; [1] (d)k Rinse the crystals collected with some cold distilled water before drying them; [1] (e)a MgCO3(s) + H2SO4(aq)  MgSO4(aq) + H2O(l) + CO2(g) [2] (f)a Mr of MgSO4 = 24 + 32 + (4 x 16) = 120 [1] Number of moles of MgSO4 formed = 2.4 / 120 = 0.02 mol [1] [2] [Total: 8]

6 (a)k The molecule contains more than one ; carbon-carbon double bond; [2] (b)a Chemical test: Add aqueous bromine / bromine water; Result: Reddish brown aqueous bromine decolourised immediately; [2] (c) (i), (ii)a [2] (iii) 72 (no marks if not indicated on graph) [1] (iv) Circle point for 2C molecule [1] [Total: 8] ------- End of Paper ------