AJC_H2 CHEM_P2 ANS

ANDE RSON JUNIOR COLLEGE 2009 PRELIMINARY EXAMINATION HIGHER 2 CHEMISTRY PAPER 2 ANSWERS 1 (a) S has more protons than Al, and since shielding effect remains almost constant, effective nuclear charge in S is larger than Al. More energy required to remove the 1 st electron from S, resulting in a higher first ionisation energy for S than Al. (b) (i) Aluminium oxide has giant ionic structure with strong electrostatic forces of attraction between Al3+ and O2- ions. Sulfur dioxide (or trioxide) has a simple covalent structure with covalent bonds between S and O atoms and weak van der Waals’ forces of attraction (i.d. – i.d.) between the molecules. (ii) Aluminium oxide is insoluble in water. Sulfur dioxide (or trioxide) dissolves in water to give an acidic solution. SO 2 (g) + H2O (l)  H2SO3 (aq) pH = 2 OR SO 3 (g) + H2O (l)  H2SO4 (aq) pH = 1 (c) (i) 2Al + 2NaOH + 6H2O  2NaAl(OH)4 + 3H2 (or ionic equation) (ii) Using pV = nRT (1.01 x 105) x (0.71 x 10-3) = n x 8.31 x (40 + 273) No. of moles of H = 2 0.0276 mol (iii) No. of moles of Al = 3 2 x no. of moles of H2 = 3 2 x 0.0276 = 0.0184 mol Mass of Al = 0.0184 x 27.0 = 0.496 g % mass of Al in alloy sample = % 1001.00 0.496  = 49.6 % (d) CC H( C H 2)7COOH HCH3(CH2)7 (e) (i) Free radical substitution AJC/2009Prelim/H2Chem/Paper2 1

Initiation : Br2 2Bruv light Propagation : CH3(CH2)3CH2CH3 + Br CH3(CH2)3CHCH3 + HBr CH3(CH2)3CHCH3 + Br2 CH3(CH2)3CHBrCH3 + Br Termination : Br + Br Br2 CH3(CH2)3CHCH3 + Br CH3(CH2)3CHBrCH3 2 CH3(CH2)3CHCH3 CH3(CH2)3CH(CH3)CH(CH3)(CH2)3CH3 (ii) Step 1: excess conc H2SO4, heat at 180oC Step 2: KMnO4 (aq), dilute H2SO4, cold (iii) CH3CH2CH2CH2CHCH3 OH 2 (a) (i) Kc =      OH R' RCOOH O H B 2 (ii) RCOOH + R’OH B + H2O initial 3 3 0 0 change - 1.94 - 1.94 + 1.94 +1.94 eqm 1.06 1.06 1.94 1.94 Kc =   2 2 06 . 1 94 . 1 = 3.35 (b) (i) There is a loss of compound B; concentration of reactants decreases and more water is for med. When amount / concentration of D decreases, according to Le Chatelier’s Principle, the position of equilibrium shifts to the right to increase D. (ii) The value of Kc remains unchanged as temperature is unchanged. AJC/2009Prelim/H2Chem/Paper2 2

(c) (i