User interface language: English | Español

Date November 2018 Marks available 1 Reference code 18N.3.sl.TZ0.4
Level SL Paper 3 Time zone TZ0
Command term Describe Question number 4 Adapted from N/A

Question

While heating solid cholesteryl benzoate, Reinitzer discovered the liquid crystal phase.

Outline two observations that he could have made.

[2]
a.

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]
b.

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]
c.

Markscheme

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.

a.

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.

b.

«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”.

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Options » A: Materials » A.4 Liquid crystals
Options » A: Materials
Options

View options