DP Chemistry (last assessment 2024)
Question 19M.3.sl.TZ1.5b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.sl.TZ1.5b |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 2]
19M.3.sl.TZ1.5b
Liquid-crystal displays (LCDs) have many uses.
A molecule which acts as a thermotropic liquid crystal is shown.
(b)
Explain the effects of very low and high temperatures on the liquid-crystal behaviour of this molecule.
Low temperature:
High temperature:
[2]
Markscheme
Low temperature:
intermolecular forces prevent molecules moving AND solid/«normal» crystal formation [✔]
High temperature:
«above a critical temperature» disrupts alignment of molecules AND behaves as fluid/liquid [✔]
Note: Accept “weak intermolecular forces break AND behaves as fluid/liquid”.
Examiners report
Very poorly answered with candidates failing to link the change in liquid crystal properties to changes in molecular motion.
