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) o separate test tubes containing compound B and C : Orange ppt formed for Compound C but not for B. Violet colouration o bserved for Compound C but not for B. Yellow ppt formed for C but not for B. (ii) o separate test tubes containing compound B and D : w ppt observed for products for med from Compound D but not for B. ellow ppt observed for products for med from Compound D but not for B. ) ) aCO3(s)  CaO(s) + CO2(g) (ii) rom Data Booklet: Zn2+ : 0.074 nm; Ca2+ : 0.099 nm is greater weakening of bonds in O3 2-.  thermal stability of ZnCO3 < CaCO3. (iii) T Add 2, 4 – DNPH (at room temperature) OR Add neutral aqueous FeCl3 (at room temperature) OR Add NaOH (aq), I2 (aq) and warm T Add dilute HCl (or H2SO4) and heat. Then add excess aqueous NaOH, aqueous I2 and warm. Yello OR Add dilute NaOH and heat. Then add aqueous I2 and warm. Y 3 (a (i C F Since Zn 2+ has a larger cationic radius than Ca 2+, the charge density of Zn 2+ is larger and it has a higher polarizing power than Ca 2+. This leads to a greater distortion of CO 3 2- electron cloud, thus there C C O OO (b) (i) s gaseous Ca 2+ and O 2- ions under standard conditions (of 298K and 1 tm). a2+ (g) + O2- (g)  CaO (s) Lattice energy of CaO is the heat evolved when one mole of solid CaO is formed from it a C AJC/2009Prelim/H2Chem/Paper2 3

(ii)  Lattice energy of CaO = - (590 + 1150) – (+657) – (147) – ½ (496) + (-635) = - 2247 kJ mol-1 (c) Step 1 Observations : Green ppt in colourless solution Cation ppted : Fe2+ Step 2 Observations : White ppt in colourless solution Cation ppted : Pb2+ 4 (a) (b) N N HC H 3 (c) 1 2 3 arginine alanine glutamic acid cathode anode Ca(s) + ½ O2(g) Ca(g) + O(g) Hat of Ca ½ B.E. of O2 CaO(s) Ca2+(g) + O2-(g) 1st & 2nd I.E. of Ca 1st & 2nd E.A. of O2 Hf of CaO L.E. of CaO pH 8.02 3.12 157.5 Volume of H 2SO4 added cm3 / AJC/2009Prelim/H2Chem/Paper2 4

5 (a) Step I : CH3Cl; heat in sealed tube Step II : NH3; heat in a sealed tube Step III : CH3COCl; room temperature (b) N HC H 3 Cl N HC H 3 NH2 B C (c) (i) N H H Cl + 3Br2 (aq) N H H Cl Br Br Br + 3HBr (ii) N CH3 N H C O O + 2 NaOH (aq) N CH3 NH2 H + 2 CH3COO-Na+ AJC/2009Prelim/H2Chem/Paper2 5