| Date | May 2018 | Marks available | 1 | Reference code | 18M.3.sl.TZ2.4 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Suggest | 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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18M.3.sl.TZ1.3b.i:
State the name given to a material composed of two distinct solid phases.
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18M.3.sl.TZ1.3a:
Discuss, in terms of its structure, why an aluminium saucepan is impermeable to water.
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18M.3.sl.TZ2.3a:
ICP-OES/MS can be used to analyse alloys and composites. Distinguish between alloys and composites.
-
17M.3.sl.TZ2.3a:
State the two distinct phases of a composite.
- 16N.3.sl.TZ0.3a: Magnesium oxide, MgO, and silicon carbide, SiC, are examples of ceramic materials. State the...
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18M.3.sl.TZ1.4e:
Suggest why there are so many different ways in which plastics can be classified. HDPE can, for example, be categorized thermoplastic, an addition polymer, having Resin Identification Code (RIC) 2, etc.
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19M.3.hl.TZ1.3a:
Identify the type of bonding in lithium hydride, using sections 8 and 29 of the data booklet.
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19M.3.sl.TZ1.3a(i):
Identify the type of bonding in lithium hydride, using sections 8 and 29 of the data booklet.
- 16N.3.sl.TZ0.3b: Predict the predominant type of bonding for a binary compound AB in which the...
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17M.3.sl.TZ2.3b:
Identify the methods of assembling nanocomposites by completing the table.
- 17N.3.sl.TZ0.4b.ii: At present, composite fillings are more expensive than amalgam fillings. Suggest why a...
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17M.3.sl.TZ1.6a:
Determine the type of bond present in SbBr3, showing your method. Use sections 8 and 29 of the data booklet.
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19N.3.sl.TZ0.5b(i):
Determine the percentage of ionic bonding in alumina using sections 8 and 29 of the data booklet.
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17N.3.sl.TZ0.4a:
Outline the composition of an alloy and a composite.
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17M.3.sl.TZ1.6b:
Lanthanum has a similar electronegativity to group 2 metals. Explain, in terms of bonding and structure, why crystalline lanthanum bromide is brittle.
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19M.3.hl.TZ2.4d:
Outline how alloys conduct electricity and why they are often harder than pure metals.
Conduct electricity:
Harder than pure metals:
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19M.3.sl.TZ2.4d:
Outline how alloys conduct electricity and why they are often harder than pure metals.
Conduct electricity:
Harder than pure metals:
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20N.3.hl.TZ0.3a:
Outline the two distinct phases of this composite.
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18N.3.hl.TZ0.2a:
Outline why this type of classification is not entirely satisfactory by using magnesium diboride, MgB2, as an example. Refer to sections 8 and 29 of the data booklet.
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18N.3.sl.TZ0.2a:
Outline why this type of classification is not entirely satisfactory by using magnesium diboride, MgB2, as an example. Refer to sections 8 and 29 of the data booklet.
-
20N.3.sl.TZ0.3a:
Outline the two distinct phases of this composite.
