C2 Material Choices

Seite 1

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.