| Date | November 2017 | Marks available | 2 | Reference code | 17N.3.sl.TZ0.7 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Deduce | Question number | 7 | Adapted from | N/A |
Question
The development of materials with unique properties is critical to advances in industry.
Low density polyethene (LDPE) and high density polyethene (HDPE) are both addition polymers.
Outline two properties a substance should have to be used as liquid-crystal in a liquid-crystal display.
Describe how the structures of LDPE and HDPE affect one mechanical property of the plastics.
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.
Many plastics used to be incinerated. Deduce an equation for the complete combustion of two repeating units of PVC, (–C2H3Cl–)2.
Markscheme
Any two of:
ability to form a LC phase
chemically stable
«LC phase that is» stable over suitable temperature range
polar
OR
being able to change orientation with applied electric field
rapid switching speed «responds to changes of voltage quickly»
Accept “ability of molecules to transmit light under certain conditions” OR “rodshaped molecules” OR “stable to light/not light sensitive”.
[Max 2 Marks]
branching in LDPE prevents close packing «of chains»
LDPE is more flexible/less rigid
OR
LDPE has lower «tensile» strength
Do not accept “difference in density”.
Award [1 max] for stating “branching in LDPE AND little/no branching in HDPE”.
B AND absence «of absorption of» C–H at 2850–3090 «cm–1»
OR
B AND presence of «absorption of» C–F at 1000–1400 «cm–1»
(–C2H3Cl–)2 (s) + 5O2 (g) → 4CO2 (g) + 2H2O (l) + 2HCl (g)
correct species in reactants and products
balanced
Accept “(–C2H3Cl–)2 (s) + 5.5O2 (g) → 4CO2 (g) + 3H2O (l) + Cl2 (g)”.
Award M2 only if M1 correct.
Examiners report
Syllabus sections
-
18M.3.sl.TZ2.4b.i:
State the chemical reason why plastics do not degrade easily.
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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.
-
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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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”.
