Question 18M.3.hl.TZ1.14
| Date | May 2018 | Marks available | [Maximum mark: 8] | Reference code | 18M.3.hl.TZ1.14 |
| Level | hl | Paper | 3 | Time zone | TZ1 |
| Command term | Apply, Deduce, Explain, Identify, State | Question number | 14 | Adapted from | N/A |
Modern electric cars store their energy in lithium ion batteries.
The diagram represents a cell in such a battery delivering a current.
Complete the half-equations on the diagram and identify the species moving between the electrodes.
[3]
Accept any balanced equation which shows Li oxidized to Li+ for M3, such as
LiC6 → Li+ + C6 + e– or
LixC6 → xLi+ + 6C + xe–
[3 marks]
State the factor that limits the maximum current that can be drawn from this cell and how electrodes are designed to maximize the current.
[2]
Limiting factor:
internal resistance «of the cell»
Electrodes design:
large surface area
Accept “time it takes ions to diffuse between electrodes”.
Accept specific ways of increasing surface area, such as “porous electrodes”.
Accept “close together/small separation”.
[2 marks]
The carbon footprint of electric cars depends on how the electricity is produced. Nuclear fission of 235U is one source of electrical energy that has a minimal carbon footprint.
Explain how the proportion of 235U in natural uranium is increased.
[3]
uranium converted to uranium hexafluoride/UF6 gas
ALTERNATIVE 1:
gas «allowed to» diffuse
lower mass isotope/235U passes through more rapidly
ALTERNATIVE 2:
use of centrifuge
higher mass isotope/238U moves/closer to outside of centrifuge
OR
lower mass isotope/235U stays in/removed from middle of centrifuge
[3 marks]
