2022 SASS A-Z Chem Prelims Ans Pt3

1 A – Z School’s Preliminary Papers 4 Express Chemistry ANSWERS: Part 3 K CHIJ Katong Convent School L Loyang View Secondary School M Montfort Secondary School N Nanyang Girls’ High School O Orchid Park Secondary School CHIJ KATONG CONVENT SCHOOL Paper 1 Paper 2 1 Sec 4 Express Pure Chemistry (6092) Preliminary Examination 2022 Marking Scheme Paper 1 (40 marks) 1 2 3 4 5 6 7 8 9 10 D D B B A C A B A A 11 12 13 14 15 16 17 18 19 20 B C D A C C A D B D 21 22 23 24 25 26 27 28 29 30 C A D C A B B B B D 31 32 33 34 35 36 37 38 39 40 D A D D A C A B A D Paper 2, Section A (50 marks) Qn Correct Response Marks A1a nitrogen dioxide 1 A1b iron(III) oxide 1 A1c lithium oxide 1 A1d calcium oxide 1 A1e silicon dioxide 1 Total 5 A2a F 1 A2b A 1 A2c B 1 A2d D 1 Total 4 A3a H2 and CrCl2 1 A3b Aluminium has an oxide layer / aluminium oxide on the surface. This forms a protective barrier/ layer around the wire, preventing the acid from reacting with it. 1 1 1 Sec 4 Express Pure Chemistry (6092) Preliminary Examination 2022 Marking Scheme Paper 1 (40 marks) 1 2 3 4 5 6 7 8 9 10 D D B B A C A B A A 11 12 13 14 15 16 17 18 19 20 B C D A C C A D B D 21 22 23 24 25 26 27 28 29 30 C A D C A B B B B D 31 32 33 34 35 36 37 38 39 40 D A D D A C A B A D Paper 2, Section A (50 marks) Qn Correct Response Marks A1a nitrogen dioxide 1 A1b iron(III) oxide 1 A1c lithium oxide 1 A1d calcium oxide 1 A1e silicon dioxide 1 Total 5 A2a F 1 A2b A 1 A2c B 1 A2d D 1 Total 4 A3a H2 and CrCl2 1 A3b Aluminium has an oxide layer / aluminium oxide on the surface. This forms a protective barrier/ layer around the wire, preventing the acid from reacting with it. 1 1 SASChemistry 2022edition

2 2 Qn Correct Response Marks A3c labelling, lesser copper atoms than zinc atoms [1] disrupted arrangement of atom layers [1] 2 Total 5 A4a no. of mol of H2SO4 =45 1000 × 0.20 = 0.009 mol [1] no. of mol of KOH =0.78 39+16+1 = 0.0139 mol (3 sf) [1] From equation, mole ratio of KOH:H2SO4 = 2:1 sulfuric acid is in excess because (2 × 0.009 = 0.018 mol) is greater than 0.0139 mol [1] / sulfuric acid is in excess because ( 0.0139 2 = 0.00695 mol) is less than 0.009 mol 3 A4b ammonia (gas) 1 Total 4 A5a Higher pressure of (gaseous) reactant(s)/ H2 and Cl2 / H2/ Cl2 There are more reactant particles/ H2 and Cl2 molecules per unit volume of the gas and they collide more frequently and there is an increase in frequency of effective collision. 1 1 A5b(i) Energy released = 184 x 2 = 368 kJ 1 A5b(ii) Energy taken in to break bonds in reactants/ hydrogen and chlorine is less than energy given out to form bonds in products/ hydrogen chloride. 1 1 Total 5 A6ai The percentage yield of ammonia decreases w