NJC 2018 A Level Chem Solution

H2 Chemistry TYS 2018 suggested answers Paper 1 Answer Key 1 D 11 C 21 C 2 D 12 D 22 A 3 D 13 A 23 B 4 B 14 A 24 D 5 C 15 A 25 A 6 D 16 A 26 B 7 C 17 B 27 B 8 C 18 A 28 C 9 C 19 C 29 D 10 B 20 D 30 D 2018 A level Paper 1 suggested answers 1) Angle of deflection ∝ charge mass Mass of electron is approximately 1 2000 the mass of a proton, hence electron has a larger angle of deflection. The charged particles are attracted to the oppositely charged plate. Ans: D 2) AlCl3 is a covalent compound with simple molecular structure. [Note: Al3+ has a high charge density with strong polarising power that can polarise the large electron cloud of Cl− significantly, leading to overlapping of electron cloud between Al and Cl. This causes the sharing of electron cloud, thus covalent bond is formed between Al and Cl] AlCl3 dimerises to Al2Cl6 as the empty 3p orbital of Al can accept a pair of electrons from Cl. Dative bond is from Cl to Al. Ans: D 3) CSeSe Se ClCl  C Cl ClClCl Around C: 2 b.p. 0 l.p. (linear) Around Se: 2 b.p. 2 l.p. (bent) Around C: 4 b.p. 0 l.p. (tetrahedral) non-polar polar non-polar Ans: D 4) Cs+, I− and Xe are isoelectronic with 54 electrons. Nuclear charge increases from I− < Xe < Cs+ while shielding effect remains constant. Nuclear attraction towards the valence electrons increases from I− < Xe < Cs+. Largest amount of energy is required to remove the most loosely held electron from Cs+. Ans: B

5) Option A is false as 1 mole of compound like Br2, contains 2 mol of atoms. Option B is false as we should only consider mass of lithium−7 isotope instead of all isotopes. Option D is false as molecular mass is the sum of average mass of the atoms in compound E. Ans: C 6) Atomic radius increases down a Group and decreases across the Period. Rb and In are both in Period 5. Atomic radius of Rb > In Ans: D 7) PO2 from air at sea level = 0.2 bar Percentage of O2 in tank = PO2 Ptotal × 100% = 0.2 4 × 100% = 5% Ans: C 8) Option A is wrong. It represents L.E. of Al2O3(s) [L.E. is when one mole of ionic solid is formed from its constituent gaseous ions] Option B is wrong. It represents 2×ΔHn [ΔHn is when one mole of H2O is formed from acid-base reaction] Option D is wrong. It represents 8×ΔHf SO2(g) [ΔHf is when one mole of compound is formed from its constituent elements in their standard state] Ans: C 9) 2×ΔHvap H2O = 890 + 410×4 + 496×2 − 805×2 − 460×4 = +72 ΔHvap H2O = +36 kJ mol−1 Ans: C

10) 0.001 mol of iodine oxide reacts with 0.01 mol of I − to gives 0.006 mol of I 2. Balancing number of I atoms on both sides, 0.006 mol of I 2 contains 0.012 mol of I atoms. Hence, 0.001 mol of iodine oxide contains 0.002 mol of iodine atoms. 0.002 mol Ix+ reacts with 0.010 mol I− to produce 0.006 mol I2. [O] 2I− ⎯→ I2 + 2e− 0.010 mol I− gives 0.010 mol of e− [R] Ix+ + ne− ⎯→ I2 0.002 mol of Ix+ gains 0.010