AJC_H1_CHEM_P2_MS

AJC JC2 PRELIM 2015 8872/02/H1 Anderson Junior College H1 Chemistry 8872 2015 JC2 Prelim Paper 2 Suggested Solutions Section A 1 (a) (i) Ionic radius of Si4+ is smaller than that of Na+. This is because both cations have the same number of electrons / electrons experience same screening effect, but Si4+ has more protons than Na+. Hence attraction of the electrons to the nucleus is stronger for Si4+. [3] (ii) P3‒ has a larger ionic radius than Si4+. This is because P3‒ has an additional quantum shell of electrons. [1]: stating difference in (i) and (ii) [1]: explanation in (i) [1]: explanation in (ii) (b) (i) Structure Bonding A Giant Ionic B Giant Covalent C Giant Ionic D Simple Covalent [1] for every 2 correct structures with corresponding bonding [2] (ii) Identity A MgO B SiO2 C Na2O D P4O10 [1] for every 2 correct identities (do not accept SO 2/SO3 for D, both are gases at rtp) [2] Explanation: A and C has good electrical conductivity when molten  giant ionic (i.e. can be Na2O, MgO or Al2O3) Since C reacts with water to form a strongly alkaline solution, C must be Na2O. Since A reacts very little with water to form a weakly alkaline solution, A must be MgO. Note: Al2O3 does not dissolve in water! B and D has poor electrical conductivity when molten  giant covalent (i.e. SiO2) or simple molecular (i.e. oxides of P or S) Since B does not dissolve in water, B must be SiO2. Since D reacts with water to form a strongly acidic solution, D must be P4O10, SO2 or SO3 (cannot be SO2/SO3 due to the high m.p. given). Note: P4O6 reacts with water to form an acidic solution of around pH 2. (c) NaCl has a giant ionic structure with strong electrostatic forces of attraction between Na+ and C l– ions. A lot of energy is required to break these strong ionic bonds in order to melt NaCl. Hence, it has a very high melting point. SiCl4 has a simple molecular structure with weak van der Waals’ forces between SiC l4 molecules. Hence, they have low melting points. [1] for one correct structure and bonding + comparison of energy and mp [2]

AJC JC2 PRELIM 2015 8872/02/H1 2 (a) (i) C14H30(l) + 2 43 O2(g) 14 CO2(g) + 15 H2O(l) [accept: 2 C14H30(l) + 43 O2(g) 28 CO2(g) + 30 H2O(l)] [1] (ii) C14H30(l) + 2 43 O2(g) 14 CO2(g) + 15 H2O(l) Bonds broken Energy Bonds formed Energy 13 C‒C 13 × 350 14×2 C=O 14 × 2 × 740 30 C‒H 30 × 410 15×2 O ‒H 15 × 2 × 460 2 43 O=O 2 43 × 496 34520 kJ mol‒1 (given out) 27514 kJ mol‒1 (taken in) Hf o (kerosene) = +27514 ‒ 34520 = ‒7006 kJ mol‒1 [1] for the 5 bonds and their correct bond energies [1] for correct no of bonds broken and formed [1] for final answer [3] (iii) 1 mol of kerosene produces 7006 kJ of energy  198 g of kerosene produces 7006 kJ of energy  1 g of kerosene produces 7006 ÷ 198 = 35.4 kJ of energy Diesel fuel is more efficient, as it produ