RI 2023 Y5 Timed Practice Solutions

© Raffles Institution 2023 9729/J/23 1 2023 Y5 H2 Chemistry July Common Test – Suggested Solutions Section A Question 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Answer D A C B C B D A C A D B C D A MCQ worked solutions Q1 (D) Relative molecular mass is the ratio of the average mass of a molecule to 1 12 the mass of a carbon -12 atom. Q2 (A) Mass of SO2 molecules in 1 m3 of air = 0.570 x 1 = 0.570 mg = 0.000570 g Amount of SO2 molecules in 1 m3 of air = 0.000570 g ÷ (32.1 + 16  2) = 0.00000889 mol Number of SO2 molecules in 1 m3 of air = 0.00000889  6.02  1023 = 5.35 x 1018 Q3 (C) % abundance of 62Ni = 100 − 69.51 − 26.78 = 3.71% Relative atomic mass of Ni in sample = (69.51  58 + 26.78  60 + 3.71  62) ÷ 100 = 58.68 Relative formula mass of Ni35Cl2 = 58.68 + 35+ 35 = 128.68 Q4 (B) 1 is correct: Mg: [Ne] 2s2 P: [Ne] 2s2 2p3 Same number of electron pairs 2 is correct: As: [Ar] 3d10 4s2 4p3 Ge: [Ar] 3d10 4s2 4p2 Same number of electron pairs 3 is incorrect: Ba: [Xe] 6s² Pb2+: [Xe] 4f¹⁴ 5d¹⁰ 6s² Different number of electron pairs Q5 (C) Option A is incorrect as X has a higher nucleon number of 36 while Y has a smaller nucleon number of 32. Option B is incorrect as X has (33 − 14) = 19 neutrons while Y has (36 − 18) = 18 electrons. Option C is correct as it fulfils all 3 criteria. Option D is incorrect as X has 14 – 4 = 10 electrons while Y has 18 electrons. Q6 (B) │Angle of deflection│is proportional to│ q m│ . 2H+:│ q m│= 1 2 18O2–:│ q m│= 2 18 = 1 9 9Be2+:│ q m│= 2 9 Statement 1 is incorrect as 2H+ particles are deflected to the largest extent. Statement 2 is correct as the │ q m│ of 9Be2+ is larger than that of 18O2–, hence 9Be2+ particles are deflected to a larger extent than 18O2– particles. Statement 3 is incorrect as 9Be2+ particles are attracted and , hence, deflected towards the negatively charged plate. Statement 4 is correct as 18O2– particles are attracted and , hence, deflected towards the positively charged plate. Hence, option B (2 and 4 only) is correct. Q7 (D) Option A is incorrect as 3 dz2 orbital consists of a dumb -bell surrounded by a small doughnut -shaped ring at its waist and aligned along the z axis. Option B is incorrect as 3 dy orbital does not exist. Option C is incorrect as the lobes of 3dx2- y2 orbital are aligned along the x and y axes. Option D is correct as 3 dxz orbital has a 4 -lobed shape and its lobes are pointing between the x and z axes. Q8 (A) Real gases deviate from ideal gas behaviour as the intermolecular attractive forces between the gas particles are significant. Ammonia has the strongest intermolecular forces of attractions (hydrogen bonding) and, hence the greatest deviation from ideality, amongst the 4 gases. The other 3 gases are non -polar simple covalent molecules with smaller electron cloud size than ammonia, thus they have weak er instantaneous dipo