NYJC Prelim_P1_P2_P3_P4_Ans

Nanyang Junior College 2017 H2 Chemistry Prelim Answers 1 2017 H2 Chemistry Prelim Answers Paper 1 Answer Key 1 B 6 D 11 A 16 D 21 D 26 C 2 D 7 B 12 C 17 A 22 B 27 A 3 C 8 A 13 C 18 B 23 A 28 A 4 C 9 A 14 D 19 D 24 C 29 A 5 C 10 A 15 D 20 B 25 B 30 D

Nanyang Junior College 2017 H2 Chemistry Prelim Answers 2 Paper 2 Answers 1 (a) (i) Shape of ammonium ion: tetrahedral Shape of nitrate ion: trigonal planar (ii) ΔHsol = -(-Lattice Energies) + (-ΔHhyd) = |L.E.| - | ΔHhyd | |L.E.| ∝ ||qq rr   | ΔHhyd | ∝ ||q r Anionic radius of nitrate ion is larger than chloride, therefore the decrease in | ΔH hyd | of nitrate ion is larg er than the decrease in |L.E.|. ΔHsol is expected to be more endothermic. (b) (i) Assuming a temperature change of 5 oC and no heat loss to surroundings, n(salt) x 15 000 = 100 x 4.3 x 5 n(salt) = 0.1433 mol minimum mass = 0.1433 x 53.5 = 7.67 g (ii) 4.0 ΔT

Nanyang Junior College 2017 H2 Chemistry Prelim Answers 3 (iii) ΔGo = ΔHo – TΔSo ΔGo is negative since reaction is spontaneous and ΔH o is positive since reaction is endothermic. Therefore sign of ΔS o is positive as there are more ways to arrange the particles when the solid dissolves in water. (c) (i) Since Zn is oxidised, Zn(s) → Zn2+(aq) + 2 e− Overall equation: Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) → Mn2O3(s) + ZnCl2(aq) + 2NH3(aq) + H2O(l) (ii) E°cell = (+0.5) – (-0.76) = +1.26V (iii) ΔGo = - nFEo = - 2 x 96500 x 1.26 = - 243 000 J mol-1 = - 243 kJ mol-1 The sign of ΔGo is negative and hence the reaction is spontaneous. 2 (a) (b) (i) Quenching is required to stop or slow down the reaction so as to achieve a more accurate titre value at that time or to find the concentration at that instance. Quenching agent: large volume of cold water / add large volume of acid to remove the NH3 (in this question). (ii) Cl2 + 2I−  2Cl− + I2 (iii) I2 + 2S2O32−  2I− + S4O62− (iv) Starch indicator is added when the solution turns pale yellow. The end -point can be recognised when one drop of sodium thiosulfate added cause the dark blue solution to permanently turn colourless.

Nanyang Junior College 2017 H2 Chemistry Prelim Answers 4 (c) (i) (ii) [2-iodobutane] = 0.20 / 2 = 0.10 mol dm-3 n(2-iodobutane) : n(I−) : n(S2O32−) = 1 : 1 : 1 n(2-iodobutane) = n(S2O32−) =