TJC Prelim P1_Worked_Solution

1 2017 JC2 Prelim H2 CHEMISTRY MCQ Worked Solution 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 B D C A D B A D B B D C D A C 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 A C A B C B C D B B A A B C C 1 Answer: B Since Ba(NO3)2  N2, Mr of Ba(NO3)2 = 261.3 No. of moles of N2 = No. of moles of Ba(NO3)2 = 1 261.3 = 3.83 x 103 mol Volume of N2 = 3.83 x 103 x 24000 = 91.8 cm3 2 Answer: D Definition – Relative molecular mass is the average mass of one molecule of an element or compound on a scale on which one atom of the 12C isotope of carbon has a mass of 12 units. Option 1 is incorrect. Relative molecular mass is a ratio. Option 2 is incorrect. It should be the ratio of the average mass of a molecule to 1/12 the mass of a 12C atom. Option 3 is correct. 3 Answer: C A is incorrect as SO 2 is an oxidizing agent and oxidises H2S in reaction. B is incorrect as SO 2 is the intermediate and is not regenerated in the reaction. C is correct as H 2S (oxidation state of sulfur is -2) is oxidized to S (oxidation state 0). D is incorrect as reaction II is a comproportionation reaction. 4 Answer: A Angle of deflection 𝛳 ∝ q/m. So 𝛳CamCa/qCa = 𝛳XmX/qX Mass of X = 20(40.1)/2 / 5.08 = 79 (Se) Atomic number of X = 34 5 Answer: D A: Ethene is a planar molecule which has all atoms on the plane B: Tri-iodide has 3 lone pairs and 2 bond pairs, hence the ion is linear and all atoms lie on the same plane C: XeF4 has 4 bond pairs and 2 lone pairs, hence shape is square planar and all atoms lie on the same plane D: BeCl42- has a total of 4 bond pairs (2 covalent bonds and 2 dative bonds) around Be atom. The shape is tetrahedral. 6 Answer: B A: HF has hydrogen bonding between its molecules and hence require a larger energy to overcome compared to pd-pd between HI molecules. B: MgO has a higher boiling point. MgO has a higher lattice energy than NaCl due to larger charge and smaller ionic radii of Mg2+ and O2- ion compared to Na+ and Cl-. C: SiH4 has a higher boiling point as its M r is larger than CH4 and thus the id-id interactions are stronger and more extensive than CH4. D: trans-C2H2Cl2 has a lower boiling point as it has no net dipole moment so the molecule is non-polar and only has id-id interactions between the molecules. cis-C2H2Cl2 has pd-pd interaction between the molecules and more energy is needed to overcome the stronger pd -pd interactions. 7 Answer: A PV = nRT At r.t.p, R = PV/nT = (1 atm x 24000 cm3)/(1 mol x 293K) Mr = mRT / PV = (m x T x 24000) / (p x V x 293) 8 Answer: D A & C: Wrong as the concentration of manganate would decrease slowly at the start of the reaction before decreasing more quickly as more Mn 2+ catalyst is generated. B: Wrong as the volume of CO 2 cannot be increasing rapidly at the start of the reaction due to slow rate of reaction. 9 Answer: B A: HBr will complete dissociate to give free H + ions and Br- ions. Since there is a chang