SAJC_H2_CHEM_P1_P2_P3_ANS Prelim

1 2011 A LEVEL PRELIM P1 SOLUTIONS 1 A 11 D 21 B 31 D 2 D 12 A 22 C 32 B 3 B 13 C 23 C 33 B 4 C 14 C 24 C 34 A 5 D 15 C 25 D 35 A 6 B 16 C 26 D 36 B 7 A 17 A 27 A 37 D 8 C 18 C 28 C 38 A 9 A 19 B 29 C 39 B 10 C 20 D 30 B 40 C 2011 Prelims (P2): Suggested Answer 1 (a) No of moles of H2SO4 = 10/1000 x 1 = 0.01 mol No of moles of NaOH = 40/1000 x 1.50 = 0.06 mol (excess) No of moles of H2O formed = 0.02 mol Amount of heat produced = 0.02 x 57 400 = 1148 J Temperature rise = 1148/(50 x 4.18) = 5.5 oC (b) Volume of FA 1 / cm3 10 20 30 40 Volume of FA 2 / cm3 40 30 20 10 Temperature rise, T / oC 5.5 11.0 8.2 / 8.3 4.1 / 4.2 (c) 1. Measure 10.0 cm3 of FA 1 using a 20 cm3 measuring cylinder. 2. Pour the FA 1 into a styrofoam cup. 3. Measure the temperature of FA 1 in the cup using a thermometer. 4. Measure 40.0 cm3 of FA 2 using another 50 cm3 measuring cylinder. Measure the temperature of FA2. 5. Take the average of the temperatures of FA1 and FA2 as the initial temperature. 6. Pour the FA 2 into the Styrofoam cup containing FA 1 and stir using the thermometer. 7. Record the maximum temperature of the mixture. 8. Repeat the experiment using the various volumes of FA 1 and FA 2 shown in the table in (b). OR 1. Measure 10.0 cm3 of FA 1 using a 20 cm3 measuring cylinder. 2. Pour the FA 1 into a styrofoam cup. 3. Measure 40.0 cm3 of FA 2 using another 50 cm3 measuring cylinder. 4. Pour the FA 2 into the Styrofoam cup containing FA 1. 5. Stir the mixture gently and record the initial temperature of the mixture using a

2 thermometer. 6. Record the maximum temperature of the mixture. 7. Repeat the experiment using the various volumes of FA 1 and FA 2 shown in the table in (b). (d) Source of error and suggestion to minimise error Heat absorbed by the calorimeter Calibration of calorimeter to account for heat absorbed (see calibration of calorimeter) Heat loss to surrounding Provide lagging on the body of the calorimeter OR Use a lid to cover the calorimeter OR Consider cooling correction (see next section) Measuring cylinders not precise in measuring volumes of FA 1 and FA 2. Use a burette to measure accurately the volumes of FA 1 and FA 2. (e) From the graph, find the point of intersection of the two lines to obtain the vol of FA 2 with maximum temperature rise. Assume vol of H2SO4 in FA 1 is V1 cm3 at point of intersection V1/1000 x [H2SO4] = (50 – V1) /1000 x 1.5/2 [H2SO4] = (50 – V1) x 1.5 2 V1 2 (a) (i) Powdered iodine has larger surface area for effective collision. Thus the rate of reaction will increase. (ii) The reaction is exothermic and has to be kept in control OR iodine may oxidise ethanol. (iii) To ensure the reaction is complete. (b) (i) CH3CH2OH + CH3CH2I  CH3CH2OCH2CH3 + HI Iodoethane undergoes nucleophilic substitution with ethanol acting as the nucleophile. (ii) I2