Question 20N.3.hl.TZ0.3
| Date | November 2020 | Marks available | [Maximum mark: 11] | Reference code | 20N.3.hl.TZ0.3 |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Classify, Deduce, Explain, Outline, Suggest | Question number | 3 | Adapted from | N/A |
Outline the two distinct phases of this composite.
[2]
carbon fibre reinforcing phase ✔
«in a» matrix phase of epoxy ✔
Award [1 max] for “reinforcing phase «embedded» in a matrix”.
Most had some idea of a composite and tended to gain at least one mark for stating "reinforcing phase embedded in a matrix".
Thermoplastic composites are increasingly replacing thermosets.
Suggest one advantage of thermoplastic polymers over thermosets.
[1]
can be recycled
OR
can be reformed when hot
OR
high impact/chemical/abrasion resistance ✔
This was well answered and most stated that one advantage of thermoplastic polymers over thermosets is that they can be recycled.
Explain how thermoplastics, such as polyvinylchloride, PVC, can be made more flexible by the addition of phthalate ester plasticizers.
[3]
Any three of:
plasticizers embed/fit between «polymer» chains ✔
keep polymer strands/chains/molecules separated/apart ✔
weaken intermolecular/London/dispersion/attractive/forces/instantaneous induced dipole-induced dipole/forces «between chains» ✔
prevent chains from packing closely/forming regular packing/structure ✔
Accept “van der Waals/vdW” for “London”.
This also was well done and some managed to score all three marks.
Explain why phthalates are replaced by other plasticizers in the production of plastics.
[2]
Any two of:
readily released into environment
OR
have weak intermolecular forces «rather than covalent bonds between chains» ✔
get into biological systems by ingestion/inhalation ✔
interrupt endocrine systems
OR
affect release of hormones
OR
effect development of male reproductive system ✔
considered carcinogenic
OR
can cause cellular damage ✔
can cause early puberty in females ✔
can cause thyroid effects ✔
can cause asthma ✔
Do not accept just “are a health concern”.
This question required an explanation of why phthalates are replaced by other plasticizers in the production of plastics. This question was found to be very challenging and even the better candidates failed to score both marks. The weaker candidates typically stated that they are just a health concern, which was deemed insufficient to warrant even a salvage mark.
Classify PVC and polyethene terephthalate, PET, as addition or condensation polymers and deduce the structural formulas.
[3]
PVC: addition AND PET: condensation ✔
structure of PVC monomer ✔
structure of PET monomers ✔
Accept full OR condensed structural formulas.
This question on PVC and PET was very well answered. All three marks for their correct classification and the corresponding structures of their monomers was frequently scored.