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.

	Criado por eshmi2471 mais de 9 anos atrás

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