RVHS_H2_CHEM_P2_ANS Prelim

RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION H2 CHEMISTRY 9647/02 Paper 2 Structured Questions Suggested Answers RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION H2 CHEMISTRY 9647/02 Paper 2 Structured Questions Suggested Answers 1. (a) (b) Amount of CaCO3 = 0.200 / Mr = 0.200 / 100.1 = 1.998 × 10-3 mol Amount of HCl required = 1.998 × 10-3 × 2 = 3.996 × 10-3 mol If limestone sample contains 100 % CaCO3, Volume of 0.100 M HCl needed = (3.996 × 10-3 / 0.100) × 1000 = 40.0 cm3 Volume used should be at least 40.0 cm3. (c) Amount of CaCO3 = 0.200 / Mr = 0.200 / 100.1 = 1.998 × 10-3 mol

River Valley High School 9647/02/PRELIM/11 Preliminary Examination 2011 2 Amount of CO2 gas evolved = 1.998 × 10-3 mol Volume of CO 2 gas = 1.998 × 10-3 × 24000 = 48 cm3 Volume of apparatus should be at least 48 cm3. (d) Measure the initial volume of gas, Vi. Lower the vial containing the rock sample into the acid to start the reaction. Measure the final volume of gas, V f, when bubbling has stopped / plunger of gas syringe has stopped moving. Let the volume of CO2 gas collected be V cm3, V = Vf - Vi Amount of CO2 gas = V / 24000 mol Amount of CaCO3 in rock sample = (V / 24000) × 1 = V / 24000 mol Mass of CaCO3 in rock sample = (V / 24000) × 100.1 = 100.1V / 24000 % mass of CaCO3 in rock sample = 100.1V 1 100%24000 0.200 = 2.09V % (e) CO2 gas may escape through the joints in the above experimental setup. Grease the joints to prevent the escape of gas. Or any reasonable answers. 2. (a) Stage 1: CH3COOH + SOCl2  CH3COCl + SO2 + HCl Stage 2: CH3COCl + C6H5NH2  N H O + HCl (b) Thionyl chloride (and/or Ethanoyl chloride formed) will react with water [1], (eventually leading to a lower yield of product). (c) (i) Ethanol is very soluble in water and separation of the two layers would be very difficult. (ii) To allow for better separation of the aqueous and organic layer.

River Valley High School 9647/02/PRELIM/11 Preliminary Examination 2011 3 (iii) (d) (i) HCl + NaHCO3  NaCl + CO2 + H2O (ii) Release the pressure in the separating funnel at intervals. (e) (i) Anhydrous calcium chloride/magnesium sulfate/sodium sulfate. (ii) nCH3COOH = 61.05 60 = 0.105 mol nSOCl2 = 20 0.94 119.1 = 0.158 mol  CH3COOH is the limiting reagent. Theoretical yield of N-phenylethanamide = 0.105  135 = 14.18 g % yield = 8.94 14.18 100%= 63.0% (iii) Recrystallisation 3. (a) (i) Nitric acid is an oxidising agent. (ii) 2Al + 3H2O  Al2O3 + 6H+ + 6e 6NO3 − + 12H+ + 6e  6NO2 + 6H2O 2Al + 6NO3 − + 6H+  Al2O3 + 6NO2 + 3H2O (iii) 2Al(s) + 2NaOH(aq) + 6H2O(l)  2NaAl(OH)4 (aq) + 3H2(g) (b) Aluminium oxide has a giant ionic structure while aluminium chloride has a simple molecular structure . A larger amount of energy is needed to overcome the strong electrostatic f