Question 19M.3.hl.TZ2.5
| Date | May 2019 | Marks available | [Maximum mark: 8] | Reference code | 19M.3.hl.TZ2.5 |
| Level | hl | Paper | 3 | Time zone | TZ2 |
| Command term | Draw, Explain, Outline, Suggest | Question number | 5 | Adapted from | N/A |
Polymers have a wide variety of uses but their disposal can be problematic.
Draw a section of isotactic polychloroethene (polyvinylchloride, PVC) showing all the atoms and all the bonds of four monomer units.
[2]
correct bonding [✔]
Cl atoms all on same side and alternate [✔]
Note: Continuation bonds must be shown.
Award [1 max] if less than or more than four units shown.
Accept a stereo formula with all atoms and bonds shown.
Few candidates scored at least one mark although most either scored both or none for this polymer structure. Some did not read that only four monomer units are required.
The infrared (IR) spectrum of polyethene is given.
Suggest how the IR spectrum of polychloroethene would diff er, using section 26 of the data booklet.
[1]
«strong additional» absorption at 600–800 «cm–1» [✔]
Almost all candidates received the mark for identifying the correct absorption band for polychloroethene.
Explain how plasticizers affect the properties of plastics.
[2]
Any two of:
embedded/fit between chains of polymers [✔]
prevent chains from forming crystalline regions [✔]
keep polymer strands/chains/molecules separated/apart [✔]
increase space/volume between chains [✔]
weaken intermolecular/dipole-dipole/London/dispersion/instantaneous dipoleinduced dipole/van der Waals/vdW forces «between chains» [✔]
increase flexibility/durability/softness [✔]
make polymers less brittle [✔]
Note: Accept “lowers density/melting point”.
This was a well-answered question; with most candidates identifying at least one method plasticizers affect the properties of plastic.
Suggest why the addition of plasticizers is controversial.
[1]
leach into foodstuffs/environment
OR
«unknown» health/environmental consequences [✔]
Note: Accept “plasticizers cannot be recycled”.
Several candidates wrote vague answers as to why the addition of plasticizers is controversial.
Outline, giving a reason, how addition and condensation polymerization compare with regard to green chemistry.
[1]
addition produces only the polymer «AND more green»
OR
addition has no by/side-product/condensation produces by-product/small molecules/HCl/NH3 «AND less green»
OR
addition has high atom economy/condensation has lower atom economy «AND less green»
OR
condensation polymers «often» more biodegradable than addition polymers «AND more green» [✔]
Note: Accept “if water produced by condensation «AND condensation and addition equally green»”.
Accept for addition “all of reactants change into products”.
Candidates seemed to have difficulty in comparing addition and condensation polymerisation with regard to green chemistry.
Draw the full structural formula of the organic functional group formed during the polymerization of the two reactants below.
[1]
[✔]
Note: Continuation bonds must be shown.
Do not accept condensed formula.
Several candidates struggled to draw the full structural formula of the peptide linkage formed during the polymerisation of the two reactants.