| Date | May 2016 | Marks available | 1 | Reference code | 16M.3.sl.TZ0.7 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | 7 | Adapted from | N/A |
Question
Chloroethene undergoes polymerization with a free-radical initiator to produce the atactic form of polychlorethene (PVC).
Sketch the atactic form of polychloroethene showing four units.
(i) Explain, in molecular terms, why PVC becomes more flexible and softer when a plasticizer is added.
(ii) State one type of compound which can be used as a plasticizer.
Suggest an environmental issue associated with the use of PVC.
Markscheme
correct structure with random orientation of Cl atoms
Accept 2-dimensional diagrams.
Accept any random arrangement of Cl atoms providing the monomer units originate from chloroethene and Cl atoms are on alternate carbons.
Continuation bonds are necessary for the mark.
(i)
«plasticizer molecules» fit between chains
OR
«plasticizer molecules» prevent chains from forming crystalline regions
OR
«plasticizer molecules» keeps strands/chains/molecules separated
OR
«plasticizer molecules» increase space/volume between chains
weakens intermolecular/dipole-dipole/London/dispersion/instantaneous induced dipole-induced dipole/van der Waals/vdW forces
Do not accept “«plasticizer molecules» lower density”.
(ii)
ester/phthalate/citrate
Accept other general or specific names of plasticizers.
does not degrade/biodegrade/break down «easily»
occupies more space in landfills
incineration produces dioxins/hydrochloric acid/HCl «which can contribute to acid rain»
Accept “plasticizer added to PVC can be a health hazard”.
Accept “combustion” for “incineration”.
Do not accept simply “toxic compounds” for M3
