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Chem Past Paper

Essay by   •  March 21, 2017  •  Exam  •  9,639 Words (39 Pages)  •  1,295 Views

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Exam Choice

2007 Chemistry Trial HSC examination.        Marking guidelines and sample answers.

Section I Part A        Multiple Choice

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D

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B

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D

Section I Part B

Question 16 (a) H9

Draws the structure of polystyrene showing 3 repeating units.

2

Draws the structure of polystyrene with one minor error.

1

sample answer:  (should except any correct, commonly used abbreviation for the benzene ring)

[pic 1][pic 2][pic 3]

Question 16 (b) H4, H13

Identifies one use of polystyrene and explains this use in terms of two of its properties.

2

Identifies one use of polystyrene and explains this use in terms of one property.

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Polystyrene 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) H9

Draws the structural formula for 1-pentanol.

1

[pic 4]

Question 17 (b) H7, H10, H14

Correctly calculates enthalpy of combustion and includes working. Answers must include units and be quoted to three or four significant figures.

3

Correctly calculates enthalpy of combustion including working. Units, significant figures unimportant.

2

Correctly does one part of the calculation.

1

q=mCΔT

q = 250 x 4.18 x 28

= 29260 J = 292.6 kJ

n = 1.55/88.151

n = 0.01758

 Heat of combustion = q/n

= 292.6 / 0.01758

= 1664 kJ/mol

= 1660 kJ/mol

Question 17 (c) H7, H10, H14

identifies that 1-pentanol's heat of combustion will be higher than ethanol's

1

 

The heat of combustion for 1-pentanol will be higher than for ethanol.

Question 17 (d) H7, H9, H14

Explains why the experimental values for 1-pentanol will be lower than the literature value.

2

Identifies that 1-pentanol's heat of combustion will be lower than the literature value.

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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, H7

  • fully compares the lead acid cell with one other type of cell, including the chemistry, impact on society, and on the environment
  • includes anode and cathode half equations

5-6

compares the lead acid cell with one other cell in terms of two of chemistry, impact on society, and impact on the environment

3-4

identifies two aspects of one cell OR identifies one aspect of each cell

2

identifies one aspect of either cell

1

lead-acid battery

hydrogen fuel cell

introduction

  • lead-acid batteries are used to provide electricity to start a car engine, and to power accessories such as lights
  • used to provide a constant source of electricity
  • supporters see them replacing the fossil-fuel based internal combustion engine in motor vehicles

chemistry

  • the electrodes are lead grids
  • the anode contains metallic lead
  • the cathode contains PbO2
  • the electrolyte is approx. 4M H2SO4

anode: 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 Pt
  • fuels (hydrogen and oxygen) must be constantly supplied

anode:

H2(g) + 2OH-(aq) → 2H2O(l) + 2e-

cathode:

O2(g) + 2H2O(l) + 4e- → 4OH-(aq)

overall: 2H2(g) + O2(g) → 2H2O(l)

impact on society

  • huge – have been partly responsible for the ease of use and widespread adoption of motor vehicles
  • essentially none on consumers at this stage  although potentially huge in the future
  • large impact considering they have been partly responsible for space exploration

impact on environment

  • the 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 storage
  • non-fossil fuel based methods of production and generation of H2 would result in massive environmental improvements

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