C2 Flashcards
Why is rubber used for car tyres?
because it is hard and elastic
what are fibres used for?
to weave cloth into clothes.
why are plastics used for objects like washing-up bowls?
they keep their shape when molded.
What is tensile strength?
the force needed to break a material when it is being stretched.
What is compressive strength?
the force needed to crush a material when it is being squeezed.
What is stiffness?
the force needed to bend a material.
What is hardness?
how well a material stands up to wear.
What is density?
the mass of a given volume of the material. It compares how heavy something is for its size.
What it the unit for density?
mass per unit volume (g/cm^3 or kg/m^3)
How are ropes made?
by winding fibres together.
What are metals?
chemicals which are shiny, malleable and electric conductors.
What are the properties of ceramics and what are 3 examples of them?
They are hard and strong. 3 EXAMPLES- Clay, glass and cement.
What are polymers?
large molecules used to make rubbers, plastics and fibres.
What is concrete?
a mixture of sand and cement.
What is bronze a mixture of?
copper and tin.
How is a nylon fibre synthesized?
by reacting chemicals in two solutions together. The solutions do not mix and instead the nylon is formed at the interface between them.
What are natural materials?
materials that are from living things which need little processing.
3 Examples of natural materials?
-paper
-wood
-silk
-cotton
wool
What natural materials are extracted from the earth’s core?
limestone, iron ore and crude oil.
What are synthetic materials?
materials that are manufactured by chemical reactions using raw materials.
What are synthetic materials alternatives to?
natural materials from living things.
Why have synthetic materials replaced natural materials?
- some natural materials are in short supply
- they are often cheaper
- they can be made in the quantity needed
- they can be designed to give particular properties.
What is crude oil (petroleum) a mixture of?
thousands of hydrocarbons.
What are hydrocarbons?
compounds of just carbon and hydrogen atoms.
What are most hydrocarbons from crude oil used as?
fuels
What is made when fuels burn in oxygen burn?
carbon dioxide and water
What does propane burn in the air to produce?
carbon dioxide and water.
How is crude oil separated?
by fractional distillation
What are the steps of fractional distillation?
- the oil is heated up which turns it all into gases.
- the distillation tower gets cooler as it gets higher
- gas molecules condense into liquids when they cool
- liquids with similar boiling points collect together. We call these fractions.
What do hydrocarbons in each fraction have?
BP’s within a range of temperatures.
When are molecule chain lengths similar?
within each fraction
The smaller the molecule chain length…
…the lower the boiling point
The smaller the molecule chain length…
…the smaller the forces between molecules.
What hold together the molecules in crude oil?
Attractive forces.
As the hydrocarbon chain length increases…
the force between these molecules increases.
Larger molecules need more energy to break them out of a liquid to form a gas and so…
they have higher boiling points.
what is a polymer?
a large molecule made by joining many smaller molecules called monomers.
What process is used to make polymers?
polymerisation
What is ethane monomer used to make?
polyethene
Different monomers produce different…
polymers
What is PET (polythene terephthatate) used for?
to make drinks bottles.
How can polymer chains be altered?
By replacing hydrogen atoms with other atoms or groups of atoms.
What does the choice of material depend on?
the properties.
When are the forces between molecules strongest?
when the molecules are close together.
The stronger the force…
- the more energy is needed to separate the molecules
- the higher the melting point
What do the properties of polymers depend upon?
how their molecules are arranged and held together.
what is LDPE and HDPE?
Low density polyethene and high density poleythene.
What does LDPE have? What does this mean?
long molecules with branches. This keeps molecule chains apart, so the force between different molecules are weak.
What properties do items made from LDPE have?
weak, flexible, soft, low melting point.
What properties do items made from HDPE have?
durable, hard, strong, stiff
What does HDPE have? What does this mean?
Long chains but no branches, so the molecules are aligned close to eachother.
LDPE has branches between the molecular chains which…
reduce the attractive forces between them.
What properties do high crystalline polymers have?
strong, high MP, can be brittle
HDPE has a degree of crystalline. What does this mean?
there are lots of areas with regular patterns in the way the molecules line up.
What does making the molecule chain longer mean?
makes it stronger
Do longer chains need less or more force to separate them?
more
what are plasticisers used for?
to make a polymer softer and to keep them apart, weakening the forces between them.
What are plasticisers?
small molecules inserted into polymer chains
what are the properties of PVC?
hardwearing, flexible and waterproof
What do cross-links do?
lock the molecules together so they cannot melt.
How can crystallinity be increased?
by removing branches on the main polymer chain and making the chains as flat as possible. This is so that the molecule chains can line up neatly.
What does drawing polymers through a tiny hole when heated do?
makes the molecule chains line up, increasing crystallinity and forming higher tensile strength fibre.
What is the width of a human hair?
0.1 mm.
What are microscopes used for?
to view small objects like human cells.
What are nanoparticles?
materials containing up to a thousand atoms.
Nanoparticles:
- occur naturally, such as salt in seaspray
- occur by accident, such as solid particulates made when fuels burn
- can be designed in labs.
What is nanotechnology?
the use and control of very small structures.
What is the size of the structures controlled in nanotechnology?
nanometres (nm)
what is a nanometre?
one millionth of a milimetre.
Why are some nanoparticles effective catalysts?
they have a large surface area. This provides more sites for reactions to take place.
What is a model of a natural nanoparticle of carbon called?
a ‘buckyball’
What does it mean that nanoparticles have very large surface areas?
they show different properties of larger particles of the same materials.
What are silver nanoparticles very good at?
killing bacteria.
Silver nanoparticles can be…
added to fibres and woven into socks; put into wound dressings; put into plastic and made into food containers.
what are titanium oxide put into? what does this mean?
sunscreen. This makes the sunscreen transparent and absorb UV light.
What are composites?
When nanoparticles are mixed with other materials like metals, ceramics and plastics.
What is the effect of adding nanoparticles to plastic sports equiptment, tennis balls and rubber tyres?
- plastic sport equiptment becomes stronger
- tennis balls stay bouncy for longer
- rubber used in tyres makes them harder wearing.
What are graphene sheets?
Individual graphite sheets one-atom thick.
Graphene sheets can be rolled into carbon nanotubes. What are these?
super-strength materials
What do sewage works use bacteria for?
to clean water
What could happen if silver nano particles are released into the environment?
they could kill lots of useful microorganisms.
What are nanoparticles used in?
cosmetics and sunscreens.
Nanoparticles are small enough to…
pass through skin into blood and into body organs.
Are the possible medical effects of nanoparticles known yet?
No.
What is one fear about nano particles in the air?
that they might be breathed in and cause lung or brain damage.
What do some people believe about the danger of nanoparticles?
Some people think that because nanoparticles occur naturally, such as in soot and volcanic dust they pose no danger.
Others think that new nanoparticles with new properties have been manufactured.
What is a risk?
the chance of an event occurring, and the consequences if it did.
