VJC_H2_CHEM_P1_Answers Prelim

2014 JC2 H2 Chemistry Preliminary Examination Paper 1 Detailed Answers 1 D 2 D 3 B 4 C 5 D 6 C 7 C 8 B 9 C 10 A 11 D 12 C 13 D 14 A 15 D 16 C 17 B 18 A 19 D 20 B 21 C 22 B 23 A 24 A 25 A 26 D 27 D 28 C 29 B 30 C 31 B 32 B 33 D 34 A 35 C 36 B 37 A 38 B 39 A 40 C 1 D Molecular formula of compound X is C4H8O2. 2 D [O]: Tl+(aq)  Tl3+(aq) + 2e– [R]: VO3 –(aq) + 6H+(aq) + 3e–  V2+(aq) + 3H2O(l) Redox: 3Tl+(aq) + 2VO3 –(aq) + 12H+(aq)  2V2+(aq) + 3Tl3+(aq) + 6H2O(l) Add 2 mol of VO 3 – to the redox equation will lead to equal number of moles of VO3 –(aq) and V2+(aq): 3Tl+(aq) + 4VO3 –(aq) + 12H+(aq)  2VO3 –(aq) + 2V2+(aq) + 3Tl3+(aq) + 6H2O(l) 3 B Option Valence shell electronic configuration of ion No. of unpaired e– A ns2np2 2 B ns2np5 1 C ns2np3 3 D ns2np2 2 4 C Option Molecule No. of electrons on central atom A 7 B 10 C 8 D 11 5 D For A, SnCl2: ~118o (2 bp, 1 lp), OCl2: 105o (2 bp, 2 lp) For B, both are bent in shape. The electronegativity of O atom is greater than that of S atom. Hence the bond pair of electrons is closer to the nucleus of O atom resulting in stronger bp–bp repulsion in H 2O and a larger bond angle for H2O. For C, both are linear in shape. For D, both are trigonal pyramidal in shape. The electronegativity of F atom is greater than that of C l atom. Hence the bond pair of electrons is further away from the N atom resulting in weaker bp–bp repulsion in NF3 and a smaller bond angle for NF3. 6 C Weak dispersion forces between CH3CH2CH3 molecules, dipole–dipole attractions between CH3CHO molecules, hydrogen bonding between CH3CH2OH molecules and hydrogen bonding between HCO2H molecules. The stronger the attractive forces between the molecules, the greater the deviation from ideal gas behaviour. HCO2H is able to form more extensive hydrogen bonding between its molecules. Hence it has a greater deviation from ideal gas as compared to CH3CH2OH. 7 C The same current flows through all the electrodes. Assuming 6 mol of e - is passed , the reactions at the various electrodes are as shown. E (oxidation): 2Al  2Al3+ + 6e– F (reduction): 6H2O + 6e–  3H2 + 6OH– G (oxidation): 6Ag  6Ag+ + 6e– H (reduction): 3Cu2+ + 6e–  3Cu Electrode F has no change in mass of electrode. Comparing the number of moles of electrode involved in the electrolysis, G has the greatest change in mass of electrode compared to E and H. 8 B Mass of water = 150.00 – 50.00 = 100.00 g Change in temperature of water = 53 – 20 = 33 oC Heat gained by water = mc∆T = (100)(4.18)(33) = 13800 J 9 C For A and B, forward endothermic reaction is favoured at higher temperature, leading to higher Kc and increase in partial pressure of NO2. For C, enthalpy change (∆H) does not change with temperature. For D, a ctivation energy is unchanged unless in the presence of a catalyst. 10 A NH3 + H2O ⇌ NH4 + + OH– For A, BaSO4 or its ions do