Copy of SCSS Prelim 2024 Chem P1 & P2 MS

1 Swiss Cottage Secondary School Preliminary Examination 2024 Secondary Four (O Level) Chemistry 6092 (Mark Scheme) – Paper 1 & 2 Paper 1 (40 marks, [1] per qn) 1 B 21 B 2 B 22 B 3 C 23 B 4 B 24 D 5 D 25 A 6 D 26 D 7 A 27 B 8 A 28 A 9 C 29 A 10 B 30 B 11 C 31 C 12 B 32 A 13 B 33 B 14 C 34 C 15 C 35 B 16 B 36 B 17 D 37 D 18 D 38 C 19 D 39 A 20 D 40 B

2 Paper 2 Section A: 70 marks Qn No. Answer marks markers’ comment A1 (a) zinc [1] (b) copper / hydrogen [1] (c) hydrogen / carbon [1] (d) argon [1] (e) fluorine [1] (f) silicon [1] Total [6] A2 (ai) The atomic radii increase down the group due to the increase in the number of electron shells [1] to hold the electrons, thus resulting in a bigger atom. [1] (aii) The atomic radii increase while electronegativity decreases as it is harder for the nucleus to attract electrons to itself. [1] [1] (aiii) 2.25 (accept value between 2.0 to 2.3). It has a larger atomic radii compared to the elements above it in the group . Since the nucleus is further away from the valence shell, it is harder for the nucleus to attract electrons. [1] [1] (bi) Melting point and boiling point decreases down the group [1] (bii) As the atomic radii increases down the group, the negatively-charged valence electrons are further away from the positively-charged nucleus. The electrostatic forces of attraction between valence electrons and the nucleus becomes weaker. [1] Less energy is required to overcome the metallic bonding/forces of attraction [1] between the valence electrons and the nucleus. [2] Total [6] A3 (a) It is because the acid contains oxygen and can dissociate/ionise in aqueous solution to form H+ ions. [1] (b) name of acid oxidation state of chlorine hypochlorous acid +1 chlorous acid +3 chloric acid +5 perchloric acid +7 [2] Every 2 correct answer [1m]

3 (c) As the oxidation state of chlorine increases, the strength of acid increases. [1] When oxidation state of chlorine increases from +1 to +7, the reaction between the acid and Mg become more vigorous. [1] [2] (d) Hypochlorous acid / HClO has the lowest electrical conductivity. It has the least vigorous reaction with magnesium and is therefore the weakest acid. This means that it must have the lowest concentration of mobile ions [1] to act as charge carriers. [1] Total [6] A4 (ai) Air is made up of a mixture of many gases, like oxygen and nitrogen. Hence • oxygen can react with hydrogen to form water if air is used during Haber process. • nitrogen reacts with oxygen to form oxides of nitrogen • air contains oxygen which oxidises iron catalyst to iron(II) oxide/iron(III) oxide • iron react with oxygen and water and rusting occurs. [choose any one point] [1] (aii) No. of mole of H2SO4 = 10.5 1000 X 0.150 = 0.001575 mol 𝑁𝑜.𝑜𝑓 𝑚𝑜𝑙𝑒 𝑜𝑓 𝑁𝐻3 𝑁𝑜.𝑜𝑓 𝑚𝑜𝑙𝑒