Chem Past Paper

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

D

A

C

A

B

D

D

D

C

C

A

C

C

D

D

Draws the structure of polystyrene showing 3 repeating units.

2

Draws the structure of polystyrene with one minor error.

1

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.

1

Draws the structural formula for 1-pentanol.

1

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

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

1

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.

1

• 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