Chem Past Paper
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Exam Choice2007 Chemistry Trial HSC examination.        Marking guidelines and sample answers.Section I Part A        Multiple Choice123456789101112131415DACABDDDCCACCDDSection I Part BQuestion 16 (a) H9Draws the structure of polystyrene showing 3 repeating units.2Draws the structure of polystyrene with one minor error.1sample answer:  (should except any correct, commonly used abbreviation for the benzene ring) [pic 1][pic 2][pic 3]Question 16 (b) H4, H13Identifies one use of polystyrene and explains this use in terms of two of its properties.2Identifies one use of polystyrene and explains this use in terms of one property.1Polystyrene is able to have gas bubbles injected into it, which make it a low density, lightweight, insulating material. Thus, this form of PS finds uses as take away cups for hot drinks. Question 17 (a) H9Draws the structural formula for 1-pentanol.1[pic 4]Question 17 (b) H7, H10, H14Correctly calculates enthalpy of combustion and includes working. Answers must include units and be quoted to three or four significant figures.3Correctly calculates enthalpy of combustion including working. Units, significant figures unimportant.2Correctly does one part of the calculation.1q=mCΔTq = 250 x 4.18 x 28= 29260 J = 292.6 kJn = 1.55/88.151n = 0.01758 Heat of combustion = q/n= 292.6 / 0.01758= 1664 kJ/mol= 1660 kJ/molQuestion 17 (c) H7, H10, H14identifies that 1-pentanols heat of combustion will be higher than ethanols1 The heat of combustion for 1-pentanol will be higher than for ethanol.Question 17 (d) H7, H9, H14Explains why the experimental values for 1-pentanol will be lower than the literature value.2Identifies that 1-pentanols heat of combustion will be lower than the literature value.1
The experimental heat of combustion for 1-pentanol will be lower than the literature value because the experimental system will lose heat to the surroundings, ie it will not be adequately insulated.Question 18 H3, H4, H7fully compares the lead acid cell with one other type of cell, including the chemistry, impact on society, and on the environmentincludes anode and cathode half equations5-6compares the lead acid cell with one other cell in terms of two of chemistry, impact on society, and impact on the environment3-4identifies two aspects of one cell OR identifies one aspect of each cell2identifies one aspect of either cell1lead-acid batteryhydrogen fuel cellintroductionlead-acid batteries are used to provide electricity to start a car engine, and to power accessories such as lightsused to provide a constant source of electricitysupporters see them replacing the fossil-fuel based internal combustion engine in motor vehicleschemistrythe electrodes are lead gridsthe anode contains metallic leadthe cathode contains PbO2the electrolyte is approx. 4M H2SO4anode: Pb(s) + SO42- (aq) → PbSO4(s) + 2e-cathode: PbO2(s) + 4H+(aq) + SO42-(aq) + 2e- → PbSO4(s) + 2H2O(l)overall: Pb(s) + PbO2(s) + 4H+(aq) + 2SO42-(aq) → 2PbSO4(s) + 2H2O(l)the electrodes are made of graphite the electrolyte can be KOH(aq)the electrodes are coated with a catalyst such as solid Ptfuels (hydrogen and oxygen) must be constantly suppliedanode: H2(g) + 2OH-(aq) → 2H2O(l) + 2e-cathode: O2(g) + 2H2O(l) + 4e- → 4OH-(aq)overall: 2H2(g) + O2(g) → 2H2O(l)impact on societyhuge – have been partly responsible for the ease of use and widespread adoption of motor vehiclesessentially none on consumers at this stage  although potentially huge in the futurelarge impact considering they have been partly responsible for space explorationimpact on environmentthe battery itself has a moderate environmental impact – rechargeable so not frequently disposed of; improper disposal releases lead into the environment (neurotoxin)by helping the widespread adoption cars, they have had a huge negative impact on the environment (CO2 from burning petrol, NOx emissions, CO emissions)from a “use” point of view they are beneficial to the environment – water is the only product of the operation of the H2 fuel cell there are environmental costs associated with their production, H2 and O2 generation and storagenon-fossil fuel based methods of production and generation of H2 would result in massive environmental improvements