| Date | May 2018 | Marks available | 3 | Reference code | 18M.3.sl.TZ1.3 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Describe | Question number | 3 | Adapted from | N/A |
Question
Aluminium and high density polyethene (HDPE) are both materials readily found in the kitchen, for example as saucepans and mixing bowls respectively. In these applications it is important that they are impermeable to water.
Both materials are also used in other applications that are more demanding of their physical properties. Carbon nanotubes are often incorporated into their structures to improve certain properties.
Discuss, in terms of its structure, why an aluminium saucepan is impermeable to water.
State the name given to a material composed of two distinct solid phases.
State one physical property of HDPE that will be affected by the incorporation of carbon nanotubes.
Describe how carbon nanotubes are produced by chemical vapour deposition (CVD).
State the property of carbon nanotubes that enables them to form a nematic liquid crystal phase.
Markscheme
«close packed» lattice of metal atoms/ions
no spaces for water molecules to pass though the structure
[2 marks]
composite
[1 mark]
melting point
OR
permeability
OR
density
OR
conductivity
OR
elasticity/stiffness
OR
brittleness/flexibility
OR
«tensile» strength
Accept “colour/transparency”.
[1 mark]
Any three of:
hydrocarbon/carbon-containing gas/compound
mixed with inert gas
heat/high temperature
«transition» metal catalyst
hydrocarbon/carbon compound decomposes to form carbon «nanotubes»
nanotubes form on catalyst surface
Accept “ethanol” or specific hydrocarbons.
Accept “N2”, “H2”, “NH3” or specific inert gases.
Accept temperature or range within 600–800 °C.
Accept specific metals such as Ni, Co or Fe.
[3 marks]
rod shaped molecules
[1 mark]
