| Date | May 2018 | Marks available | 1 | Reference code | 18M.3.sl.TZ2.4 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | State | Question number | 4 | Adapted from | N/A |
Question
Propene can polymerize to form polypropene.
Propene monomer: 
Sketch four repeating units of the polymer to show atactic and isotactic polypropene.
State the chemical reason why plastics do not degrade easily.
Compare two ways in which recycling differs from reusing plastics.
Civilizations are often characterized by the materials they use.
Suggest an advantage polymers have over materials from the iron age.
Markscheme
Do not accept syndiotactic (alternating orientation of the CH3 groups), eg,
for M1 or M2.
Accept any correct atactic ordering of CH3 groups.
Penalize missing hydrogens or incorrect bond connectivities once only.
Accept skeletal structures.
Ignore continuation bonds, brackets and “n” indices in structures.
[2 marks]
strong covalent bonds
Accept “moisture cannot get inside the plastic matrix, and bacteria cannot live without moisture, so they cannot attack the polymer chains”.
Accept “bacteria lack the enzymes required to break down the hydrocarbon chains”.
[1 mark]
Any two of:
Recycling: shredded/melted/reformed AND Reuse: used in its current form
recycling is more energy intensive «than reusing»
recycling degrades the quality of plastic but reusing «typically» does not
recycling breaks down original product to form a new product whereas reuse extends product life
[2 marks]
more pliable/flexible materials
OR
more durable/non-corrosive/longer-lasting materials
OR
greater variety of materials
OR
lower density
OR
can be clear/translucent
Accept “more adaptable”.
Do not accept just “more useful”.
[1 mark]
Examiners report
Syllabus sections
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19M.3.sl.TZ1.4c(ii):
The trace quantities of dioxins from tyre fires are rarely inhaled and instead settle on the ground.
Describe why this is a health concern.
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19M.3.sl.TZ2.5e:
Suggest why the addition of plasticizers is controversial.
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19M.3.hl.TZ2.5d:
Suggest why the addition of plasticizers is controversial.
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17N.3.sl.TZ0.7b.ii:
One of the two infrared (IR) spectra is that of polyethene and the other of polytetrafluoroethene (PTFE).
Deduce, with a reason, which spectrum is that of PTFE. Infrared data is given in section 26 of the data booklet.
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17N.3.sl.TZ0.7c:
Many plastics used to be incinerated. Deduce an equation for the complete combustion of two repeating units of PVC, (–C2H3Cl–)2.
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18N.3.sl.TZ0.2d:
Repeating units of several polymers are listed.
The infrared (IR) spectrum of one of these polymers is shown.
Deduce, giving a reason, the name of this polymer and its Resin Identification Code (RIC), using sections 26 and 30 in the data booklet.
- 19N.3.hl.TZ0.5c: Discuss why the recycling of plastics is an energy intensive process.
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18N.3.sl.TZ0.2b.ii:
In an incomplete combustion of the polyvinyl chloride, PVC, it was found that hydrogen chloride, carbon monoxide, carbon dioxide, and water vapour were released.
Formulate an equation for this reaction using the formula of the PVC repeating unit.
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18M.3.sl.TZ1.4d:
Suggest two of the major obstacles, other than collection and economic factors, which have to be overcome in plastic recycling.
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18M.3.sl.TZ2.4b.ii:
Compare two ways in which recycling differs from reusing plastics.
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19M.3.hl.TZ1.4c:
Tyre fires emit trace quantities of polychlorinated dibenzofurans and polychlorinated dibenzo-p-dioxin.
Outline, using section 31 of the data booklet, why polychlorinated dibenzofuran is not classed chemically as a dioxin but considered “dioxin-like”.
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19M.3.sl.TZ2.5c:
Identify a hazardous product of the incineration of polychloroethene.
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19M.3.sl.TZ1.4c(i):
Tyre fires emit trace quantities of polychlorinated dibenzofurans and polychlorinated dibenzo-p-dioxin.
Outline, using section 31 of the data booklet, why polychlorinated dibenzofuran is not classed chemically as a dioxin but considered “dioxin-like”.
