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Melting point
The temperature at which a solid melts into a liquid
Conductivity
How well a material conducts electricity
Strength
The ability of a material to resist an applied force
Hardness
How well a material can resist being scratched or indented
Brittleness
How easily a material breaks when a force is applied
Stiffness
How well a material can resist bending
What are ceramics?
A group of hard, brittle, heat-resistant, and corrosion-resistant materials
How are ceramics made?
By shaping and then firing a non metallic material, such a clay, at a high temperature
What are two main groups of ceramics?
Clay ceramic and glass
What are examples of clay ceramics?
Brick, china and porcelain
How are clay ceramics made?
By shaping wet clay while it's soft and then heating it to a high temperature in a furnace, which causes it to harden
Why can bricks be used for building?
Because they have a high compressive strength
What type of glass is the glass we use most of?
Soda-lime glass
How is soda lime glass made?
by melting a mixture of sand (silicon oxide), sodium carbonate and limestone, then allowing the molten liquid to cool and solidify.
How is borosilicate glass made?
By heating sand with boron trioxide - has a much higher melting point than soda lime glass
Why is glass useful for windows?
It is transparent, strong, and a good thermal insulator
Composite material
Consists of two or more materials with different properties that have been combines to produce a material with more desirable properties
What two components are most composite materials made from?
The reinforcement and the matrix
What is the reinforcement?
Long solid fibres or fragments
What is the matrix?
Binds the reinforcement together - usually something that starts soft and then hardens
Polymers
Large molecules of high relative molecular mass and are made by linking large numbers of smaller molecules called monomers
What does the properties of a polymer depend on?
The monomers from which it was made and the conditions of the chemical reaction
What are the properties of polymers?
flexible, easily shaped, and good insulators of heat and electricity.
What two main forms does poly(ethene) come in?
- low density poly(ethene) LDPE
- high density poly(ethene) HDPE
What are the conditions to make LDPE?
- moderate temperatures
- high pressure
- catalyst
What are the properties of LDPE?
More flexible but weaker
What are the uses of LDPE?
Carrier bags
What are the conditions to make HDPE?
- low temperature
- low pressure
- catalyst
What are the properties of HDPE?
More rigid and stronger
What are the uses of HDPE?
Drainpipes
Thermosoftening polymers
- Lots of polymer chains held together by weak intermolecular forces
- these break easily when heated causing the polymer to melt
- it can then be remoulded into a different shape and will harden again when cooled
Thermosetting polymers
- made from lots of polymer chains held together by strong covalent bonds
- these require lots of energy to break so dont soften when heated
- these polymers are hard, strong and rigid
What are the properties of metals?
Malleable, ductile, good to conductors of heat/electricity, high mp and bp
What are alloys?
Metals with atoms of another element mixed - much stronger than pure metals
What are alloys useful for?
Purposes where they might be put under stress like in buildings
Corrosion
The process by which metals are slowly broken down by reacting with substances in their environment
Example of corrosion
Rusting of iron
Equation for the rusting of iron
Iron + oxygen + water —-> hydrated (iii) iron oxide
What happens at the atomic level to the iron during rusting?
The iron atoms are each losing 3 electrons to become iron 3+ ions
What happens at the atomic level to the oxygen during rusting?
The 2 oxygen atoms in each molecule are gaining two electrons to become o2- ions
Why is the reaction of the Rusting of iron a redox reaction?
The iron becomes oxidised as it loses 3 electrons
The oxygen becomes reduced as it gains 2 electrons
What needs to be present for rusting to take place?
Water and oxygen
Why is it only the surface of a metal that corrodes?
It is only the surface that is exposed to the substances in the environment
Why can the entire chunk of iron break down eventually by rust if left long enough?
Each layer flakes off revealing a new layer which will also flake off
What happens when metals like aluminium corrode?
Only the surface atoms are affected - forms a protective layer of aluminium oxide which protects the rest of the metal from the environment
How can we prevent iron from rusting?
Barrier methods and sacrificial methods
How do barrier methods work?
By preventing oxygen and water from touching the iron so that rusting can't take place
What are examples of barrier methods?
Painting, oil/grease, electroplating
How do sacrificial methods work?
Adding a more reactive metal like aluminium or zinc to the iron means that if the object is exposed to oxygen, the more reactive metal will be oxidised instead
What is an example of preventing rust that uses both barrier and sacrificial methods?
Galvanising - coating the iron object in a layer of zinc
What is meant by sustainable?
Meets the needs of current generations without jeopardising the lives of future generations
What is one way we can develop more sustainably?
By using renewable resources rather than finite resources
What are ways to reduce the environmental impact of the manufacturing process?
- making processes more efficient
- using catalysts to reduce the amount of energy used
What is the most sustainable thing to do once we've finished using a product?
Reusing and recycling
Life Cycle Assessment (LCA)
An assessment of the different stages in a products life cycle in order to assess its impact on the environment
What are the 4 main stages of LCAs?
- extracting an processing the raw materials
- manufacturing and packaging your product
- using your product
- disposing of it
How does extracting raw materials damage the local environment?
- cutting down forests
- mining
How does processing raw materials indirectly damage the environment?
- huge amounts of energy are required for extracting metals from their ores or the fractional distillation of crude oil
- pollutants can be released
What are the 3 main problems associated with manufacturing and packaging?
- energy use
- pollution
- waste products
What can be done with waste products if they aren't disposed of?
They can be used as raw materials for something else
What needs to be considered when assessing the impact of using a product?
- how much damage it does during its lifetime e.g. pollution
- how long the product is used for
What is wrong with using landfills?
- takes up space that could've been used for nature
- chemicals might seep out into the surrounding ecosystems
Why is burning waste bad?
Releases pollutants into the atmosphere
What is the raw material for plastic bags?
crude oil needs to be separated by fractional distillation - uses high amounts of energy
What is the raw materials for paper bags?
Wood from trees - reduces habitat available for animals and plants
How are plastic bags manufactured?
Hydrocarbons from fractional distillation are cracked to make alkenes which undergo polymerisation to make plastics
How are paper bags manufactured?
Timber has to be pulped - requires loads of energy, produces waste
Can plastics bags be reused multiple times?
Yes
Can paper bags be reused multiple times?
No
How are plastic bags disposed of?
Not biodegradable, take up space in landfills, can get out into the wild and harm animals
How are paper bags disposed of?
biodegradable, non-toxic and can be recycled
Why is the manufacture of products involving loads of different steps a limitation of lifecycle assessments?
- it is almost impossible to quantify all of the steps
- it is difficult to assess the harm of each step
Why is the fact that LCAs are so complex a limitation of LCAs?
- they can be manipulated to deliberately support a company (positive advertising)
Potable water
water that is safe to drink
What is pure water?
contains only water molecules (boils at exactly 100'C)
Why isn't potable water pure water?
It contains dissolved substances
What are the 3 criteria for water to be considered potable?
- levels of dissolved substances need to be fairly low
- has to have a pH between 6.5 and 8.5
- no microorganisms
What does the source of potable water depend on?
Where in the world you live
Where is water in the UK obtained?
- from the rain, collected as groundwater or surface water
What are examples of surface water sources?
Lakes, rivers, reservoirs
What are examples of ground water sources?
Aquifers - areas of permeable rock underground and trap water
Benefits of using surface water
- easy to access
- gets replaced frequently by the rain
Why is ground water relied on instead in hotter areas of the UK?
If its hot and sunny, surface water can dry up as it is exposed to the sun
How is water treated?
- fresh water is passed through a wire mesh to filter big things
- passed through a bed of sand and gravel to filter out smaller bits
- sterilised to kill harmful microbes
How is water sterilised?
- bubbling chlorine gas
- exposing to ozone or ultraviolet light
Desalination
A process of removing salt from ocean water
What are the two main techniques for desalination?
Distillation and reverse osmosis
Why are the processes of distillation and reverse osmosis somewhat impractical for producing large amounts of water?
- requires a lot of energy so expensive
How is water desalinated by distillation?
- water is boiled
- water vapour is condensed and collected to give us pure distilled water
How is water desalinated by reverse osmosis?
Salty water is passed through a membrane which only allows water molecules to passed through minerals and ions get trapped and separated leaving pure distilled water
What are the 3 main sources of waste water?
Domestic, agricultural systems and industrial
What are examples of domestic waste?
Waste from showers, sinks, toilets
What are examples of agricultural waste?
Nutrient run off, animal waste
What is an example of industrial waste?
Waste from factories that use/make chemicals
How does sewage treatment work?
- (screening) the sewage is passed through gratings and meshes to remove anything large
- (sedimentation) the sewage is left to sit in a settlement tank so that the heavier particles settle at the bottom as sludge whilst the lighter particles settle at the top as effluent
- air is pumped through the effluent to supply the bacteria with oxygen to undergo aerobic digestion
- the sludge is sealed in a container to prevent entry of air which ensures anaerobic respiration
What are the other uses for sludge once it has been digested?
Releases methane gas from the anaerobic digestion so can be burnt as a fuel, can be used as fertiliser as it contains many nutrients
How can toxic chemicals in sludge be removed?
By adding chemicals to precipitate out any metals or using uv radiation
Why do some countries rely on treating waste water rather than desalinating salt water?
As it is easier
How is the ammonia made from the haber process used?
Used as a starting material for fertilisers, dyes, explosives
Where is the nitrogen used in the haber process obtained?
From the air