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Date May 2014 Marks available 5 Reference code 14M.3.hl.TZ1.10
Level HL Paper 3 Time zone TZ1
Command term Deduce, Describe, and Outline Question number 10 Adapted from N/A

Question

Liquid crystals are widely used in devices such as calculators, laptop computers and advanced optical materials.

Kevlar® is a material used in bullet-proof vests.

(i)     Deduce the products formed by a condensation polymerization reaction of the monomers benzene-1,4-diamine and benzene-1,4-dicarbonyl chloride to form Kevlar®.

M14/4/CHEMI/HP3/ENG/TZ1/10.c.i

(ii)     Describe the factors which account for the inherent strength of Kevlar®.

 

 

 

 

 

 

(iii)     Outline why Kevlar® can dissolve in concentrated sulfuric acid.

Markscheme

(i)     M14/4/CHEMI/HP3/ENG/TZ1/10.c.i/M ;

Brackets or n not necessary but continuation bonds must be shown.

Do not penalise if CO and NH are in cis configuration.

HCl;

Allow correct name for M2.

(ii)     Kevlar® (molecules) have strong covalent bonds (so hard to break);

(large number of) hydrogen bonds between C=O and NH groups;

CO/NH groups trans to each other so orientation maximizes interactions/helps packing/produces more ordered structure / \(\pi \)-bonding/aromatic stacking interactions between benzene rings in neighbouring strands / OWTTE;

(iii)     intermolecular forces/hydrogen bonds broken / nitrogen and oxygen atoms become protonated / reverses condensation process / OWTTE;

Examiners report

In (c) (i), continuation bonds were frequently omitted and \({{\text{H}}_{\text{2}}}{\text{O}}\) was often stated incorrectly instead of HCl. In (ii) although some candidates mentioned the hydrogen bonding network in Kevlar® often they did not state that these intermolecular forces are between the C=O and NH groups. (iii) was generally answered correctly.

Syllabus sections

Options » A: Materials » A.9 Condensation polymers (HL only)
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