NYGH 2018-S3EOY-IP Chem P1 & P2 Ans

Secondary 3 (IP) EOY Answers 2018 Sec 3 End-of-Year Exam Chemistry Answers Paper 1 1 B 2 D 3 B 4 A 5 B 6 D 7 D 8 B 9 D 10 B 11 B 12 A 13 B 14 D 15 D 16 B 17 D 18 C 19 A 20 C 21 D 22 D 23 C 24 D 25 A 26 D 27 C 28 C 29 A 30 B Explanations for Paper 1 MCQ Explanations 1 Substance B has boiling point between 0 to 25 °C None of the other substances has melting or boiling points between 0 to 25 °C 2 During melting, heat energy supplied (option A is not true) is used to overcome attractive forces between particles B: Particles will have kinetic energy at all temperatures except for 0 K C: No chemical reaction is occurring 3 Separating funnel: used to separate 2 or more immiscible liquids A: aqueous solution of NH4Cl and Pb(NO3)2 present B: aqueous KI will form immiscible layer with CHCl3 C: aqueous solution of NaNO3 and KNO3 present D: insoluble solid + liquid present 4 When cooled to room temperature, since lead(II) sulfate is insoluble at room temperature, it will crystallise à crystals can be separated from the mixture by filtration, obtaining crystals as residue 5 Since gas is collected by upward delivery à gas must be less dense than air à average Mr of gas must be less than average Mr of air (28.9) à gas must be H2 6 Best choice of indicators will be 1 indicator which changes colour just below pH of 4.5 (methyl orange), and 1 indicator which changes just above pH of 4.7 (methyl red) 7 A strong acid ionises completely in water to form H+ ions and anions 8 Ionic equations for reactions: (1) 2H+(aq) + MgO(s) à Mg2+(aq) + H2O(l) (2) 2H+(aq) + 2K(s) à 2K+(aq) + H2(g) (3) Ba2+(aq) + SO42–(aq) à BaSO4(s) Since H+ ions are not involved in reaction 3, H2SO4 is not behaving as an acid

9 Titration: used to prepare soluble group 1 and ammonium salts à only options A and D Precipitation: used to prepare insoluble salts à only options A, B and D Adding excess solid reactants: used to prepare soluble salts that are not group 1 or ammonium salts à only options B, C and D Only option D is correct for all 3 methods 10 Since metallic oxides are already expected to be basic, an equation showing that the metallic oxide is also acidic (ie a reaction with base/alkali) will show that metallic oxide is amphoteric à option B shows the metal oxide reacting with OH– C: Reaction of metal oxide with H+ just confirms the fact that it is basic 11 From topic of QA, Pb(OH)2 is insoluble in excess aqueous ammonia, while Cu(OH)2 is soluble in excess aqueous ammonia to form dark blue solution Therefore Pb(OH)2 can be obtained by adding aqueous ammonia and filtering D: Cu(OH)2 will be obtained instead of Pb(OH)2 12 Test with KI: Pb2+ present Test with aqueous NaOH, Al: NO3– present (Note that NH4+ could also be present but answer cannot be option D as SO42– cannot be present since R is a colourless solution) 13 Same observations if NH3(aq) or NaOH(aq) added Different observations if H2SO4(aq): white precipitate formed if Pb2+ is present, no observable change if Al3+ is present No