OCR 21st Century C2

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What is tensile strength?
The force needed to break a material when it is stretched.
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What is compressive stength?
The force needed to crush a material when it is squeezed.
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What is stiffness?
The force needed to bend a material.
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What is hardness?
How well a material stands up to wear (i.e. being scratched).
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What is density?
Mass of a given volume of material.
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List 3 materials that are extracted from the Earth's crust.
Limestone, iron ore and crude oil.
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Why are synthetic materials often favoured over natural materials?
They are cheaper, manufactured to give particular properties, and can be better than using up the limited resource of natural materials.
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What is crude oil made of?
Hydrocarbons (chain molecules up to 100 carbon atoms long).
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Describe fractional distillation.
Crude oil is heated up into a gas. | The distillation tower it is heated in gets cooler as it gets higher. | Gas molecules condense into liquids when cooled. | Liquids of similar boiling points cool in the same places, forming fractions.
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What is the effect of a smaller molecule chain length on the forces between the molecules?
They are smaller/weaker forces.
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Why do larger molecules have higher boiling points?
More energy is needed to turn them from a liquid into a gas.
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What is a polymer made of?
A chain of monomers.
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What is the name of the process that creates polymers?
Polymerisation.
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Which monomer is used to make polythene?
Ethene.
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When are forces between molecules strongest?
When molecules are close together.
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Why are the forces between low density polythene (LDPE) monomers weak?
Because it's made up of long molecules with branches, which keep the molecule chains apart.
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Why is HDPE stronger?
They have long chains also, but no branches, which makes the molecules closer.
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What is crystallinity? Where is it found? Waht is the effect of it?
Many of the molecules line up in similar patterns. It can be found in HDPE, and makes the polymer strong and with a high melting point, but also brittle.
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What are plasticisers? How are they used?
They are small molecules put into a polymer to hold the chains apart, making the forces weaker and the material softer.
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What is the difference between a thermoplastic and a thermosetting plastic, in terms of how they react when heated?
Thermoplastics soften, and can be molded; thermosetting plastics do not.
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What is cross linking?
When molecules are locked together, and cannot melt.
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How do nanoparticles occur? Give 3 ways.
Naturally, in seaspray (salt); accidentally, in burning fuels (particulates); in laboratories (designed).
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How big is a nanometre in comparison to a millimetre?
One millionth smaller.
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What makes some nanoparticles good catalysts?
A large surface area.
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What are silver nanoparticles used for?
Killing bacteria. Because of this, they are added to fibres, put into wound dressings, or made into food containers.
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Why is it dangerous to make plastic wrap out of nanoparticles?
They may come off on the wrapped food, resulting in us ingesting some of them.
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What is the risk of using nanoparticles?
They are small enough to pass through the skin, into the blood and organs. The medical effects are still unknown, but they are feared to cause lung and brain damage.
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What are titanium oxide nanoparticles used for?
Sunscreen; making it transparent and able to absorb UV light.
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What is the effect of adding nanoparticles to other materials?
Makes plastic sports equipment stronger; makes tennis balls bouncy for longer; makes rubber tyres harder wearing.
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What is the danger associated with silver nanoparticles?
If released, they could kill a lot of useful micro-organisms in our environment. They can also be washed out of clothes into sewage works, and kill the useful bacteria that clean sewage water.
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Other cards in this set

Card 2

Front

What is compressive stength?

Back

The force needed to crush a material when it is squeezed.

Card 3

Front

What is stiffness?

Back

Preview of the front of card 3

Card 4

Front

What is hardness?

Back

Preview of the front of card 4

Card 5

Front

What is density?

Back

Preview of the front of card 5
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