Chemistry - Topic 10 - Using Resources
Ceramics, Composites and Polymers
Ceramics come in many different forms
Ceramics are non-metal solids with high melting points.
Some ceramics can be made from clay; clay is a soft material when it's dug up out of the ground. Its ability to be moulded when wet and then hardened makes it ideal for making pottery and bricks.
Most glass made is soda-lime glass, which is made by heating a mixture of limestonesand and sodium carbonate until it melts. When the mixture cools it comes out as glass.
Composites are generally made of two different materials
Composites are made of one material embedded in another. Fibres or fragments of a material (known as the reinforcement) are surrounded by a matrix acting as a binder.
Fibreglass consists of fibres of glass embedded in a matrix made of polymer (plastic). It has a low density but is very strong. It's used for things like skis, boats and surfboards.
Carbon fibre composites also have a polymer matrix. The reinforcement is either made from long chains of carbon atoms bonded together (carbon fibres) or from carbon nanotubes. These composites are very strong and light so are used in aerospace and sports car manufacturing.
Concrete is made from aggregate (a mixture of sand and gravel) embedded in cement. It's very strong which makes it ideal for use as a building material.
Wood is a natural composite of cellulose fibres held together by an organic polymer matrix.
Polymers can have very different properties
High density (HD) poly(ethene) is also made from ethene but at a lower temperature and pressure with a different catalyst. It's more rigid and is used for water tanks and drainpipes.
The monomers that a polymer is made from determine the type of bonds that form between the polymer chains. These weeks bonds determine the properties.
Low density (LD) poly(ethene) is made from ethene at a moderate temperature under a high pressure and with a catalyst. It's flexible and is used for bags and bottles.
Thermosoftening polymers contain individual polymer chains entwined together with weak forces between the chains: can melt and remould them.
Two important things that can influence the properties of a polymer are how it's made and what it's made from.
Thermosetting polymers contain monomers that can from cross-links between the polymer chains holding them in a solid structure. these polymers don't soften when they are hearted, they are strong hard and rigid.
Properties of Materials
Different materials are suited to different jobs
Polymers are insulators of heat and electricity, they can be flexible (they can be bent without breaking) and are easily moulded. Polymers are used in clothing and insulators in electrical items.
The properties of composites depend on the matrix/binder and the reinforcement used to make them, so they have many uses.
Ceramics include glass and clay ceramics such as porcelain and bricks. They're insulators of heat and electricity, brittle (they aren't very flexible and break easily) and stiff.
Metals are malleable, good conductors of heat and electricity, ductile (can be drawn into wires), shiny and stiff. Metals have many uses, including in electrical wires, car body-work, and cutlery.
Pure metals don't always have the Properties needed
The regular structure of pure metals often means they are too soft for everyday use.
Alloys are made by mixing a metal with other element(s). These elements disrupt the regular structure of the metal, making it harder.
Alloys
Brass = Copper + Zinc: More malleable and causes less friction. Used in plumbing and door fittings.
Gold alloys are used to make jewellery as gold is a very soft metal. Pure gold is 24 carat. 18 carat gold is 18/24 parts gold.
Bronze = Copper + Tin: Harder than copper. Used to make medals and decorative ornaments.
Aluminium alloys are used to make aircraft. Aluminium has a low density which is important in aircraft, however it is too soft if not in an alloy.
Corrosion
Iron and Steel corrode much more than aluminium
rust is iron+oxygen+water->hydrated iron(III) oxide
Corrosion only happens on the surface of a material where it's exposed to the air.
Iron needs to be in contact with both oxygen and water which is present in air.
Rust is a soft crumbly solid that flakes off to leave iron be able to rust again, eventually all iron corrodes away.
Iron corrodes easily. (rusts)
Both air and water are needed for ion to rust
If you put an iron nail in a boiling tube with just air, it won't rust.
If you put an iron nail in a boiling tube with air and water, it will rust.
If you put an iron nail in a boiling tube with just water, it won't rust.
There are two main ways to prevent rusting
Prevented by coat the iron with a barrier to keep out water and oxygen.
Electroplating - uses electrolysis to reduce the metal ions onto an iron electrode.
Oiling/Greasing - has to be when moving parts are involve.
Painting/Coating with plastic.
Sacrificial method, involves placing an more reactive metal with the iron so it is sacrfised instead of the iron.
Galvanised by spraying it with zinc.
Finite and Renewable Resources
Natural Resources come from the Earth, sea and air
2) Some of these natural products can be replaced by man-made
processes.
3) Agriculture provides conditions where natural resources can be enhanced for our needs.
1) Natural resources form without human input. They include anything that comes from the earth, sea or air.
Some natural resources will run out
1) Renewable resources reform at a similar rate to, or faster than, we use them.
2) Finite (non-renewable) resources, aren’t formed quickly enough to be considered replaceable.
3) Finite resources include fossil fuels and nuclear fuels such as uranium and plutonium. Minerals and metals found in ores in the earth are also non-renewable materials.
Extracting finite resources has risks
2) People have to balance the social, economic and environmental effects of extracting finite resources.
e.g. mining metal ores brings in hobs but is bad for then environment.
1) Many modern materials are made from raw, finite resources,
for example most plastics.
Reuse and Recycling
Chemistry is improving sustainability
As well as using resources, extracting resources. Processing the resources into useful materials unsustainable too, as the processes often use energy produced from finite resources.
One way of reducing the use of finite resources is for people to use less. This doesn't just reduce the use of that resource but also anything needed to produce it.
Sustainable development is an approach to development that takes account of the needs of present society while not damaging the lives of future generations.
We can't stop using finite resources altogether, but chemists can develop and adapt processes that use lower amounts of finite resources and reduce damage to the environment. For example, chemists have developed catalysts that reduce the amount of energy required for certain industrial processes.
Copper-Rich ores are in short supply
Traditional methods of copper mining are damaging to the environment. These new methods of extraction have a much smaller impact, but the disadvantage is that they're slow.
Copper is a finite resource. One way to improve its sustainability is by extracting it from low-grade ores. Scientists are looking into new ways to do this: Bioleaching (using bacteria) and phytomining (growing plants that collect copper from the soil).
Recycling metals is important
Depending on what the metal will be used for, different amounts of separation are needed. For example, iron and steel can be kept together as they can be added to a blast furnace to reduce the amount of iron ore needed.
Mining and extracting metals usually uses more energy than recycling them. It also cuts down the amount of finite metal that is extracted from the earth.
Glass can also be recycled
Glass bottles can often be reused without reshaping.
Other forms of glass can’t be reused so they’re recycled instead. Usually the glass is separated by colour and chemical composition before being recycled.
Glass recycling can help sustainability by reducing the amount of energy needed to make new glass products.
The glass is crushed and then melted to be reshaped for use in glass products such as bottles or jars.
Life Cycle Assessments
Life Cycle Assessments show total environmental costs
Manufacture and Packaging: Manufacturing products and their packaging can use a lot of energy resources and can also cause a lot of pollution. You also need to think about any waste products and how to dispose of them. Some waste can be turned into other useful chemicals, reducing the amount that ends up polluting the environment.
Using the Product: The use of a product can damage the environment. For example, burning fuels releases greenhouse gases and other harmful substances. How long a product is used for or how many uses it gets is also a factor.
Getting the Raw Materials: Extracting raw materials needed for a product can damage the local environment, e.g. mining metals. Extraction can also result in pollution due to the amount of energy needed.
Product Disposal: Products are often disposed of in landfill sites. This takes up space and pollutes land and water. Energy is used to transport waste to landfill, which causes pollutants to be released into the atmosphere. Products might be incinerated (burnt), which causes air pollution.
A life cycle assessment (LCA) looks at every stage of a product’s life to assess the impact it would have on the environment.
You can compare life cycle assessments for plastic and paper bags
Manufacturing: Plastic (fractional distillation, cracking and polymerisation. Less waste as other oils are used). Paper (pulped timber is processed using lots of energy and making lots of waste).
Use: Plastic (can be reused). Paper (usually only used once).
Resources: Plastic (crude oil), Paper (timber)
Disposal: Plastic (recyclable? and not biodegradable?, will take up space in landfills). Paper (biodegradable, non-toxic and can be recycled).
There are problems with LCAs
2) So, producing an LCA is not an objective method as it takes into account the values of the person carrying out the assessment. This means LCAs can be biased.
3) Selective LCAs, only show some of the impacts of a product on the environment deliberately support the claims of a company, in order to give them positive advertising.
1) The use of energy, some natural resources and the amount of certain types of waste produced by a product over it’s lifetime can be easily quantified.
Potable Water
Potable water is water you can drink
The way that potable water is produced depends on where you are
2) Pure water only contains H2O molecules
whereas potable water can contain lots of other dissolved substances.
3) Salt levels cant be high - no bacteria and pH is between 6.5 and 8.
1) Potable water is water that’s been treated or is naturally safe for humans to drink.
5) In some very dry countries they instead use sea water must be
treated by desalination to provide potable water.
6) Distillation can be used to desalinate sea water.
4) Even though it only has low levels of dissolved substances, water from these fresh water sources still needs to be treated to make it safe before it can be used.
7) Sea water can also be treated by processes that use membranes — like reverse osmosis. Ions and larger molecules are trapped by the membrane so separated from the water.
3) In the UK, the source of fresh water used depends on location. Surface water tends to dry up first.
2) When it rains, water can either collect as surface water or ground water.
1) Rainwater is a type of fresh water. Fresh water is water that doesn’t have much dissolved in it.
Waste Water Treatment
Waste water comes from lots of different sources
3)Sewage gas it be treated to romove any harmful matter before put back into rivers.
4)Industrial process such as the harbour process produce a lot of waste water that has to be treated.
2)Agricultural systems also produces a lot of waste water including nutrient run-off from fields and slurry from animal farms.
Sewage Treatment happens in several stages
4) The sludge from the bottom of the settlement tank is also removed and transferred into large tanks. Here it gets broken down by bacteria in a process called anaerobic digestion.
5) Anaerobic digestion breaks down the organic matter in the sludge, releasing methane gas in the process. The methane gas can be used as an energy source and the remaining digested waste can be used as a fertiliser.
3) The effluent in the settlement tank is removed and treated by biological aerobic digestion. This is when air is pumped through the water to encourage aerobic bacteria to break down any organic matter — including other microbes in the water.
6) For waste water containing toxic substances, additional stages of treatment may involve adding chemicals, UV radiation or using membranes.
2)settlement tank and undergoes sedimentation — the heavier suspended solids sink to the bottom to produce sludge while the lighter effluent floats on the top.
Sewage treatment requires more processes than treating fresh water but uses less energy than the desalination of salt water, so could be used as an alternative in areas where there’s not much fresh water.
1) Before being treated the sewage is
screened- this involves removing
any large bits of material
The Haber Process
Nitrogen and Hydrogen are needed to make Ammonia
2) The hydrogen mainly comes from reacting methane gas with steam to form hydrogen and carbon dioxide.
3) The reactant gases are passed over an iron catalyst. A high temperature (450 ºC) and a high pressure are used.
1) The nitrogen is obtained easily from the air.
4) Because the reaction is reversible some of the ammonia produced converts back into hydrogen and nitrogen again.
This reaction is well suited for an industrial scale as the reactants aren’t too difficult or expensive to obtain.
5) The ammonia is formed as a gas, but as it cools in the
condenser it liquefies and is removed. The unused hydrogen
(H2), and nitrogen, (N2), are recycled, so nothing is wasted.
The Haber process is used to make ammonia from hydrogen and nitrogen = N2 (g) + 3H2 (g) <> 2NH3 (g) (+ heat)
6) The ammonia produced can then be used to make ammonium nitrate — a very nitrogen-rich fertiliser.
The reaction is reversible, so there's a compromise to be made
5) The 450 °C is a compromise between maximum yield
and speed of reaction.t’s better to wait just 20 seconds for a 10% yield than to have to wait 60 seconds for a 20% yield.
6) Higher pressures move the position of equilibrium
towards the products. So increasing pressure maximises the
percentage yield. It also increases the rate of reaction.
4) The trouble is, lower temperatures mean a slower rate of
reaction (and so equilibrium is reached more slowly).
7) So the pressure is set as high as possible, without making the process too expensive to or dangerous to build and maintain. Hence the 200 atmospheres operating pressure.
3)e.g. the forward reaction in the Haber process is exothermic.
increasing the temperature will move the equilibrium the wrong way away from ammonia and towards nitrogen and hydrogen. Yield of ammonia would be greater at lower temperatures.
NPK Fertilisers
NPK Fertilisers provide plants with the essential elements for growth
2)Three elements in fertilisers are nitrogen, phosphorus and potassium. If they don't get enough there life processes are affected.
3)Fertilisers replace these missing elements or provide more of them, helps increase the crop yield and grow faster.
1)Manure to fertilise fields as they are better and widely available.
4)Formulations conatiaing salts of nitrogen (N) phosphorus (P) and potassium (K) so NPK.
Ammonia is used to produce nitrogen-containing compounds
3)They react and produce ammonium nitrate - good compound to use in fertilisers as it has two sources of nitrogen
2)You can also react ammonia with acids, including nitric acid, to get ammonium salts.
Industry : done in giant vats, high concentrations resulting in a exothermic reaction. The heat released is used to evaporate water from the mixture - very concentrated solution.
1)Ammonia can be reacted with oxygen and water is a series of reactions to make nitric acid.
Lab : Smaller scale by titration and crystallisation. Much lower concentration, so less heat it produced by the reaction and is safer for a person to carry out. Crystallisation is very slow.
Phosphate and Potassium are sourced from mined compounds
1)Potassium chloride and potassium sulphate can be mined and used as a source of potassium.
2)Phosphate rock is also mined. However because its insoluble plants can't use them as nutrients.
Reacting phosphate rock with a number of different types of acids produces soluble phosphates
Reaction with sulphuric acid produces calcium sulphate and calcium phosphate (single superphosphate)
Reaction with phosphoric acid only produces calcium phosphate (triple superphosphate)
Reaction with nitric acid produces phosphoric acid and calcium nitrate.
Aluminium also corrodes when exposed to air, its not completely destroyed by corrosion, aluminium oxide forms and doesn't flake away is a protective layer.
5)As well as organic matter industrial waste water contains harmful chemicals.
1)When you flush any water it goes to the sewers.
2) These factors can also affect the position of equilibrium for a reversible reaction — and sometimes there is a trade-off between increasing the rate and maximising the yield of a reaction.
8) And finally, the iron catalyst makes the reaction go faster, but doesn’t affect the yield.
1)The temperature and pressure, can affect the rate of a reaction.
5) After they’ve been extracted, many finite resources undergo man-made processes to provide fuels and materials necessary for modern life. e.g fractional distillation
8) Both of distillation and reverse osmosis need loads of energy, so they’re really expensive and not practical for producing large quantities of fresh water.
Filtration — a wire mesh screens out large twigs etc,
and then gravel and sand beds filter out any other solid bits.
Sterilisation — the water is sterilised to kill any harmful
bacteria or microbes. This can be done by bubbling chlorine gas through it or by using ozone or ultraviolet light.
(practical)