| Date | May 2019 | Marks available | 2 | Reference code | 19M.3.sl.TZ1.5 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
Liquid-crystal displays (LCDs) have many uses.
A molecule which acts as a thermotropic liquid crystal is shown.
State the name of the functional group which allows the molecule to be responsive to applied electric fields.
Explain the effects of very low and high temperatures on the liquid-crystal behaviour of this molecule.
Low temperature:
High temperature:
Markscheme
nitrile [✔]
Note: Accept “cyano".
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
A few students correctly named the nitrile group as being the one responsible for the polarity of the liquid crystal molecule.
Very poorly answered with candidates failing to link the change in liquid crystal properties to changes in molecular motion.
Syllabus sections
-
18M.3.sl.TZ1.3b.iv:
State the property of carbon nanotubes that enables them to form a nematic liquid crystal phase.
- 16N.3.sl.TZ0.7b: Explain the effect of increasing the temperature of a nematic liquid crystal on its...
- 18N.3.sl.TZ0.4b: The structure of biphenyl nitrile is shown. Describe, giving a reason, a feature of the...
- 18N.3.sl.TZ0.4a: Outline two observations that he could have made.
-
18M.3.sl.TZ1.4a:
Both of these are thermoplastic polymers. Outline what this term means.
-
19M.3.sl.TZ1.5a:
State the name of the functional group which allows the molecule to be responsive to applied electric fields.
-
19M.3.hl.TZ1.5a:
Label with an asterisk, *, the chiral carbon atom.
- 16N.3.sl.TZ0.7a: Outline how a lyotropic liquid crystal differs from a thermotropic liquid crystal.
- 19N.3.sl.TZ0.6b: State how liquid crystals are affected by an electric field.
- 19N.3.sl.TZ0.6a: Describe the arrangement of soap molecules in the nematic liquid crystal phase.
-
18M.3.hl.TZ2.6b:
MWCNT are very small in size and can greatly increase switching speeds in a liquid crystal allowing the liquid crystal to change orientation quickly.
Discuss two other properties a substance should have to be suitable for use in liquid crystal displays.
-
17M.3.sl.TZ2.6a:
Two important properties of a liquid crystal molecule are being a polar molecule and having a long alkyl chain. Explain why these are essential components of a liquid crystal molecule.
-
18M.3.sl.TZ2.5b:
Discuss three properties a substance should have to be suitable for use in liquid crystal displays.
-
19M.3.hl.TZ2.3:
Describe the characteristics of the nematic liquid crystal phase.
Shape of molecules:
Distribution:
- 20N.3.hl.TZ0.4e: Experiments have been done to explore the nematic liquid crystal behaviour of CNT. Justify...
-
19M.3.sl.TZ2.3:
Describe the characteristics of the nematic liquid crystal phase and the effect that an electric field has on it.
Shape of molecules:Distribution:
Effect of electric field:
-
19M.3.hl.TZ1.5b:
Explain the effects of very low and high temperatures on the liquid-crystal behaviour of this molecule.
Low temperature:
High temperature:
- 20N.3.sl.TZ0.4d: Experiments have been done to explore the nematic liquid crystal behaviour of CNT. Justify...
-
17N.3.sl.TZ0.7a:
Outline two properties a substance should have to be used as liquid-crystal in a liquid-crystal display.
