Notas
C2 Material Choices
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C2 – Material Choices
C2.1
How do we measure the properties of materials and why are the results useful?
Ø
An
element is made up of one type of atom and these can be found in the periodic
table.
Ø
A
compound is made up of two or more elements.
Ø
A
material can be made from polymers, metals, glasses and ceramics to make all
sorts of objects and structures.
Ø
The
properties can be the physical or chemical characteristics of a
material/chemical.
Ø
We
can change the properties of a material to make it different from others e.g.
boiling point, melting point, structure, bonding.
Ø
A
material can have any of these properties to make it more suitable for its
purpose:
1.
Tension
means how much stretching force is needed to break the material.
2.
Compression
means how much squashing force is required to break the material.
3.
Stiffness
means how hard it is to bend the material.
4.
Hardness
means how difficult it is to scratch or dent the material.
5.
Melting
point means how hot the material has to be before it breaks out into a liquid.
6.
High
density means that the material is heavy for its size.
7.
Low
density means that the material is light for its size.
8.
A
STRONG material is hard to break.
9.
A
SOFT material can be scratched or dented easily.
C2.2
Why is crude oil important as a source of new materials such as plastics and
fibres?
Ø
Natural
materials are any product or physical matter that originates from plants,
animals or the ground e.g. cotton, paper, silk – these can be obtained from
living things.
Ø
Synthetic
materials tend to be man-made using chemicals e.g. plastics, polythene
Ø
Synthetic
materials are alternatives to materials from living things.
Ø
Raw
materials from the earth’s crust can be used to make synthetic materials.
Ø
A
polymer is a man-made substance which can be used as plastics that allow its
properties to be altered in order to suit different purposes. It can often
replace natural materials which don’t often work for the purpose, thus making
it better.
Ø
A
polymer is a molecule made up of many repeating hydrocarbons.
Ø
Monomers
are smaller molecules that aren’t joined together and when they do they make up
a long polymer molecule.
Ø
If
the monomers join, they form a long polymer and this process is called
polymerisation.
Ø
The
longer the molecules of a polymer, the higher the melting point. This is
because forces between the molecules are stronger therefore more energy is
required to overcome these forces and separate the molecules. So long chained
polymer molecules are stronger and less likely to break.
Ø
This
is the opposite for short chained polymer molecules. They tend to have a lower
melting point because less energy is required to overcome the forces between
the molecules. Therefore short chain polymer molecules are weaker and more
likely to break.
Ø
Crude
oil consists mainly of hydrocarbons, which are chain molecules of varying
lengths made from carbon and hydrogen atoms only.
Ø
Hydrocarbons
are mixtures of carbon and hydrogen compounds and atoms that aren’t chemically
bonded together.
Ø
The
strength of the forces between hydrocarbon molecules in crude oil depend on the
amount of energy needed for them to break out of a liquid and form a gas to the
temperature at which the liquid boils.
Ø
Only
a small percentage of crude oil is used for chemical synthesis and most of it
is used as fuels.
Ø
The
petrochemical industry refines crude oil by fractional distillation –
hydrocarbons are separated into fractions of different boiling points, to
produce fuels, lubricants and the raw materials for chemical synthesis.
Ø
Materials
which have superior properties have replaced materials used in the past.
C2.3
Why does it help to know about the molecular structure of materials such as
plastics and fibres?
Ø
It
is possible to produce a wide range of different polymers with properties that
make them each suited to a particular use.
Ø
The
properties of a polymer depend on how their molecules are arranged and held
together.
Ø
Modifications
in polymers produce changes to their properties. These modifications include;
1.
Increased
chain length – the material becomes stronger, stiffer and the melting point
gets higher. Stronger forces of attraction.
2.
Cross-linking
– chemical bonds to link together the chains of some polymers. It makes the
material tougher and less flexible.
3.
The
use of plasticizers – small molecules added to polymers during their
manufacture. They push polymer molecules slightly further apart, weakening the
forces between them. This makes the material softer and more flexible.
4.
Increased
crystallinity – makes the material hard, high in tension, stiff and it tends to
have a high melting point.
C2.4
What is nanotechnology and why is it important?
Ø Nanotechnology is the use
and control of very small structures called nanoparticles which equivalent to
the size of some molecules. (1-100 nanometres in size)
Ø Nanoparticles can occur
naturally e.g. sea spray or by accident e.g. smallest particulates from
combustion of fuels.
Ø They can also be designed.
Ø Nanoparticles of a
material show different properties compared to larger particles of the same
material.
Ø Nanoparticles can be used
to modify the properties of materials.
Ø Examples include;
1. The use of silver
nanoparticles to give antibacterial properties.
2. Adding nanoparticles to
plastics for sports equipment to make them stronger.
Ø
Some
nanoparticles may have harmful effects on health and there is concern that
products with nanoparticles are being introduced before these effects have been
fully investigated.