MJC 2015_H1_CHEM P2_MS Prelims

1 ©meridian jc 2015 MJC Prelim H1 Paper 2 Suggested Answers 1 (a)(i) P Cl Cl Cl x x x x x (ii) (b) Both PCl3 and PCl5 have simple molecular structure. Size of electron cloud: PCl3 < PCl5 Extent of polarisation of electron cloud: PCl3 < PCl5 Extent of van der Waals’ forces between molecules: PCl3 < PCl5 Energy required to break forces between molecules: PCl3 < PCl5 Boiling point: PCl3 < PCl5 (c) (i). Rate of forward reaction = the rate of reverse reaction. (ii) Kc = 32 5 [PC ] [C ] [PC ] ll l mol dm–3 (iii) Kc = (0.1016) (0.1016) (0.0984) = 0.105 mol dm–3 (iv) When volume is de creased, pressure is increased . The equilibrium position shifts to the left to reduce number of mole of gas to decrease pressure . When pressure increased, concentration of reactant particles increases and particles are closer to each other. Frequency of effective collision of reactant particles increases so rate of reaction increases. (v) Reduction is due to oxidation number of P decrease from +5 in PC l5 to +3 in PCl3. Oxidation is due to oxidation number of C l increases from –1 in PCl5 to 0 in Cl2. 2(a)(i) Al (g)  Al+ (g) + e (ii) Across the period, increase in nuclear charge outweighs negligible increase in screening effect . Effective nuclear charge increases across the p eriod. Stronger

2 ©meridian jc electrostatic attraction between nucleus and first valence electrons. First ionisation energy generally increases. (iii) .The 3p electron in Al is further away from the nucleus than the 3s electron in Mg. (b)(i) (bii) SiCl4 + 2H2O  SiO2 + 4HCl PCl5 + 4H2O  H3PO4 + 5HCl (ci) (ii) 1. giant ionic lattice structure with strong electrostatic force between oppositely charged ions 2. amphoteric (iii) Al2O3 + 6HCl  2AlCl3 + 3 H2O Al2O3 + 2NaOH + 3H2O  2NaAl(OH)4 3(a)(i) ΔHrxn = [2(350) + 610 + 8(410) + 2(460)] – [3(350) + 360 + 460 + 9(410)] = –50 kJ mol–1 (ii) The bond energies from the Data Booklet are average values. (bi) No. of moles of butan-1-ol = 0.972 74.0 = 0.01314 mol Quantity of heat absorbed by water = 20482 J BeO Na2O Al2O3 SO2 1.87 2.52 1.83 0.86

3 ©meridian jc Quantity of heat released by reaction = 100 80 x 20482 J ΔHc(butan-1-ol) = – 25602.5 0.01314 = –1950 kJ mol–1 (ii) The process is not 100% efficient. Some of the heat released by the combustion of butan- 1-ol is lost to the surrounding. (c) Add aqueous iodine in sodium hydroxide to each alcohol respectively and heat. Yellow ppt of tri-iodomethane, CHI3, is observed for the secondary alcohol. No yellow ppt is observed for butan-1-ol. (d)

4 ©meridian jc Section B : Free Response Questions 4 (ai) Starting material to synthesize polypropene (used as plastic in food containers). (ii) Carbon monoxide causes blood poisoning which prevents transport of oxygen by haemoglobin. U