Practise Edexcel IAL Chemistry 19.10 by explaining hydrogen bonding between polyamide chains and suggesting physical-property benefits of modified polymers.
This question is about benzene and some of its compounds.
Semi-aromatic polyamides have high melting temperatures, high strength and rigidity and are resistant to chemical attack so they have many applications in engineering.
Explain why polyamides have higher melting temperatures than polyalkenes.
An answer that makes reference to the following point:
- because there is hydrogen bonding (and London forces between the chains) in a polyamide
- (and this is) stronger than the London forces between the chains in polyalkenes (so more energy is needed to separate the polyamide molecules) or the London forces between the chains in polyalkenes are weaker (than hydrogen bonding so more energy is needed to separate the polyamide molecules)
Reference to breaking of covalent bonds scores (0) Ignore references to (permanent) dipole forces
Allow 'it' for the polyamide since it is the subject of the question, so "it has hydrogen bonding" scores M1
Do not award if hydrogen bonding to water stated Do not award if hydrogen bonding shown by CH2 Do not award if ionic bonding or ions referred to
Accept dispersion forces / attractions between temporary and induced dipoles for London forces Allow van der Waals’ forces for London forces
Allow London forces in polyalkenes are easier to overcome (than hydrogen bonding)
Note that M2 is awarded for a comparison of the weakness of London forces to the strength of hydrogen bonding. Hence M2 is dependent on M1 or near-miss
COMMENT
Reference to polyalkenes "only having London forces" compared to polyamides having hydrogen bonding is not enough for M2 unless the hydrogen bonding is stated to be strong
Allow reference to molecules rather than chains
(2)