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Date May 2018 Marks available 3 Reference code 18M.3.sl.TZ2.5
Level SL Paper 3 Time zone TZ2
Command term Discuss Question number 5 Adapted from N/A

Question

Chemical vapour deposition (CVD) produces multi-walled carbon nanotubes (MWCNT) of a more appropriate size for use in liquid crystals than production by arc discharge.

State the source of carbon for MWCNT produced by arc discharge and by CVD.

[2]
a.

Discuss three properties a substance should have to be suitable for use in liquid crystal displays.

[3]
b.

Markscheme

Arc discharge:

graphite electrode

OR

hydrocarbon solvent

 

CVD:

gaseous hydrocarbons

 

Accept “carbon electrode”.

Accept specific examples of suitable hydrocarbon solvents (eg, methyl benzene/toluene OR cyclohexane).

Accept specific examples of suitable gaseous hydrocarbons (eg, methane, ethane, ethyne/acetylene) OR carbon monoxide OR carbon dioxide.

[2 marks]

a.

Any three from:

chemically stable AND does not «chemically» degrade over time

stable over range of temperatures AND to avoid «voltage/random shift» fluctuations ✔

polar AND influenced by an electric field

strong intermolecular forces AND allow molecule to align in specific orientations ✔

rapid switching speed/low viscosity AND change orientation «quickly» when electric field is applied/reversed

 

Award [1 max] for identifying three correct properties without any discussion or incorrect interpretation of suitability.

Accept “voltage” for “electric field”.

[3 marks]

b.

Examiners report

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

Syllabus sections

Options » A: Materials » A.4 Liquid crystals
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