Question 18N.3.sl.TZ0.4
| Date | November 2018 | Marks available | [Maximum mark: 5] | Reference code | 18N.3.sl.TZ0.4 |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Describe, Outline, Predict | Question number | 4 | Adapted from | N/A |
While heating solid cholesteryl benzoate, Reinitzer discovered the liquid crystal phase.
Outline two observations that he could have made.
[2]
Any two of:
cloudy/foggy/hazy phase «at first melting point» ✔
clear liquid phase «at second melting point/higher temperature» ✔
two «different» melting points
OR
new phase observed over a wide temperature range ✔
Accept “exhibit both liquid and solid properties at the same time” for M3.
The structure of biphenyl nitrile is shown.
Describe, giving a reason, a feature of the molecular structure, other than its polarity, that allows biphenyl nitrile to show liquid crystal behaviour.
[1]
ALTERNATIVE 1:
«bulky/long» C5H11/R/alkyl «group/chain» AND prevents molecules from packing closer together «to form solid state» ✔
ALTERNATIVE 2:
biphenyl «fragment»/two benzene rings/two aromatic rings AND «makes molecule» rigid/rod-shaped ✔
Accept “rigid/rod-shaped molecule, so aligns with other molecules” for ALTERNATIVE 2.
Arc discharge, consisting of two inert metal electrodes in a liquid solvent, is one method of producing carbon nanotubes (CNTs).
Predict, giving a reason, the electrode at which the solvent cyclohexane, C6H12, will decompose to form CNTs.
[2]
«average» oxidation state of C in C6H12/cyclohexane = –2 AND in CNTs = 0
OR
oxidation state of C in CNTs is higher than in C6H12/cyclohexane
OR
loss of H’s/hydrogens ✔
«oxidation at» anode/positive/+ «electrode» ✔
Accept “oxidation number” for “oxidation state”.