Using Resources

• Renewable resources: sources of power that are used as quickly as they are produced

  Finite resources: have a limited supply that will eventually run out

  Sustainability: which is development that meets the needs of current generations without compromising the ability of future generations to meet their own needs
• • Humans use the Earth’s resources to provide warmth, shelter, food & transport

  • Natural resources, supplemented by agriculture, provide food, timber, clothing & fuel

  • Finite resources from the Earth, oceans & atmosphere are processed to provide energy & materials

  • Chemistry plays an important role in improving agricultural & industrial processes to provide new products and in sustainable development
• • Potable water is water that is safe to drink – it is essential for life

  o potable water isn’t chemically pure because it contains dissolved substances (isn’t just H2O)

  o the levels of dissolved salts and microbes in water has to be sufficiently low for human consumption

  o also it needs to have a pH of between 6.5 and 8.5
• • In the UK, rain provides water with low levels of dissolved substances (fresh water) that collects as surface water (lakes, rivers, reservoirs) or as groundwater (in rocks underground called aquifers that trap water)

  • The methods used to produce potable water depend on the availability of water and local conditions

  • Most potable water is produced by:

  o choosing an appropriate source of fresh water

  o passing the water through filter beds (wire mesh for twigs, gravel and sand beds for other solids)

  o sterilising (killing microbes)
• • Sterilisation agents used to produce potable water are:

  o chlorine gas

  o ozone

  o ultra violet light

  • If only salty/sea water is available then desalination is required, can be done by:

  o distillation (requires lots of heat) OR

  o reverse osmosis (passing the water through multiple layers of membranes which trap molecules)

  o BOTH are very expensive as the require lots of energy (not practical for large volumes of water)
• Method – testing and distilling water

  1. Test the pH, if it is not between 7 you need to neutralise it using a titration (use a pH meter instead of an indicator as this would contaminate the water)

  2. Then test the sample for sodium chloride (the main salt in seawater) using a flame test for sodium ions (would turn yellow if present) and then to test for chloride ions add a few drops of silver nitrate solution and if a white precipitate forms they are present
• Method – testing and distilling water

  3. To distil water, pour the salty water into a conical flask and heat the flask from below, the water will evaporate

  leaving any dissolved salts. The steam will condense into liquid water in the condenser

  4. Then retest the distilled water for sodium chloride and test the pH (there should be no sodium chloride and the

  pH should be 7)
• • Urban lifestyles and industrial processes produce large amounts of waste water that require treatment before being released into the environment

  o Sewage and agricultural waste water require removal of organic matter and harmful microbes

  o Industrial waste water many require the removal of organic matter and harmful chemicals
• Sewage treatment

  • Screening and grit removal

  o the water is passed through mesh screens to remove any large bits of material e.g. twigs and plastic bags as well as any grit

  • Sedimentation to produce sewage sludge and effluent

  o the water is then allowed to stand in a settlement tank where sedimentation occurs

  o the heavier suspended solids sink to the bottom producing sludge, the lighter effluent floats on top

  ▪ sometimes chemicals are added to make the solids and microbes stick together to sink
• Sewage treatment

  • anaerobic digestion of sewage sludge

  o the sludge at the bottom of the tank is removed and transferred to large tanks

  o the sludge is broken down by anaerobic respiration by bacteria

  o the methane gas produced can be used as an energy source and digested sludge as fertiliser
• Sewage treatment

  • aerobic biological treatment of effluent

  o the effluent from the top of the tank is removed and treated by biological aerobic respiration (air is

  pumped through the water to encourage aerobic bacteria to break down any organic matter)

  o the effluent is then sterilised with chlorine, ozone or UV to kill any remaining microbes

  o this effluent can now be released into the environment
• it is cheaper to obtain potable water from groundwater and waste water over salt water, but salt water is more abundant so is good for countries with physical water scarcity
• Phytomining – using plants to absorb metal compounds

  • plants are grown on soil that contains copper; the ions aren’t used within the plant so they build up in the leaves

  • the plants are harvested and burned in furnaces, the ash contains copper compounds
• Bioleaching – using bacteria to produce leachate solutions containing metal compounds

  • bacteria are used to convert copper compounds in low-grade ore into soluble copper compounds

  • the leachate produced by this process contains copper ions which can be extracted

  • the metal compounds produced can be processed to obtain the metal

  o copper metal from the displacement with scarp iron or by electrolysis
• Pros of biological methods of extraction:

  • Very small impact on the environment
  • Can use low grade copper ores
• Pros of traditional metal extraction:

  • Much faster, simpler process
• Life Cycle Assessment

  o extracting and processing raw materials

  ▪ extracting materials can damage the local environment and result in air pollution due to the

  amount of energy required

  ▪ raw materials often need to be processed to extract the desired material which is very energy

  intensive e.g. fractional distillation of crude oil

  o manufacturing and packaging

  ▪ these processes are energy intensive and can produce atmospheric pollutants and harmful

  fumes e.g. carbon monoxide

  ▪ some waste products from chemical reactions used may be harmful to the environment
• Life Cycle Assessment

  o use and operation during its lifetime

  ▪ the use of a product can damage the environment e.g. fertilisers can leach into water supply damaging ecosystems

  ▪ products that are long lasting have a smaller impact

  o disposal at end of use

  ▪ products disposed of in landfill take up space and pollute the ground

  ▪ energy is used to transport items to landfill releasing atmospheric pollutants e.g. NO

  ▪ products may be incinerated causing air pollution
• • Corrosion is the gradual destruction of materials by chemical reactions with substances in the environment e.g.

  o rusting is the corrosion of iron

  o both air and water are required for rusting to occur

  o reaction: iron + oxygen + water → hydrated iron(III) oxide

  o the rust flakes leaving iron exposed to further rusting
• • Corrosion can be prevented by applying a coating that acts as a barrier e.g.

  o greasing (helps prevent corrosion when moving parts are involved)

  o painting (works for all surfaces, decorative too!)

  o electroplating (electrolysis to reduce metal ions onto an iron electrode, the new metal coating doesn’t corrode)

  o aluminium has an oxide that protects the metal from further corrosion (doesn’t flake like rust)
• • Some coatings are reactive and contain a more reactive metal to provide a sacrificial protection e.g.

  o zinc/magnesium is used to galvanise iron

  o the more reactive metal reacts with the oxygen and water instead of the metal below
• • most metals in everyday use are alloys e.g.

  o bronze (copper + tin) – harder than copper, used for medals, decorative ornaments and statues

  o brass (copper + zinc) – more malleable than bronze, used in areas of low friction e.g. taps

  o gold – pure gold is soft; silver, zinc and copper are used to harden gold – used for jewellery

  ▪ 24 carat gold is pure gold, 18 carat gold is 75% gold and 25% other metals

  o aluminium alloys - used to make aircraft because it is low density

  ▪ pure aluminium is too soft, alloys make it stronger
• Steels are an alloy of iron and a specific amount of carbon

  o high carbon steel – strong, brittle, inflexible (bridges) 0.3-2.5% carbon

  o low carbon steel – soft, easily shaped (car bodies) 0.1-0.3% carbon

  o stainless steel – hard, corrosion-resistant (cutlery) iron+nickel/chromium
• • Ceramics are non-metal solids with high melting points made from non-carbon-based compounds

  o clay-ceramics e.g. brick and pottery – are made by shaping wet clay then heating in a furnace

  • Types of glass:

  o Most is soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone

  o Borosilicate glass is made from sand and boron trioxide (melts at higher temp. than soda-lime glass)
• • Composites are made of one material embedded in another - fibres of a material (reinforcement) are

  surrounded by a matrix (binder) e.g.

  o Fibre glass – glass fibres in a matrix of plastic, low density (like plastic) but strong (like glass)

  o Carbon fibre – carbon nanotube reinforcement in a polymer matrix, light and strong

  o Concrete – aggregate (sand and gravel) fibre in cement matrix, very strong

  o Wood – natural composite of cellulose fibres in a organic polymer matrix
• Polymers

  o properties depend on the monomers they are made from + the conditions under which they were made

  o e.g. poly(ethene)’s properties depend on the temperature, pressure and catalyst

  ▪ Low density (LD) poly(ethene) – moderate temp, high pressure (flexible – for bags)

  ▪ High density (HD) poly(ethene) – low temp, low pressure, different catalyst (rigid – for tanks)

  ▪ HD has a higher melting point than LD because it has higher forces of attraction
• Polymers

  o the monomers used determine the types of bonds that form between the polymer chains:

  ▪ thermosoftening polymers – individual, tangled polymer chains which are easily separated, can be melted and remoulded

  ▪ thermosetting polymers – monomers form cross-links between them – creating a solid structure which don’t soften when heated (strong, rigid, hard)
• The Haber Process

  • The Haber process is used to manufacture ammonia, which can be used to produce nitrogen-based fertilisers

  • the raw materials are nitrogen and hydrogen

  o nitrogen is easily obtained from the air (78% oxygen)

  o hydrogen is obtained from reacting methane with steam to form hydrogen (and carbon dioxide)
• Process of Haber Process

  • the purifies gases are passed over an iron catalyst at 450°C and 200atm

  • because the reaction is reversible some ammonia produced is converted back into nitrogen and hydrogen

  • the ammonia formed is a gas, but as it cools it condenses so is removed as a liquid

  • the unused hydrogen and nitrogen are recycled (nothing is wasted)
• Haber Process

  Condition compromises (dynamic equilibrium)

  • the conditions are 450°C and 200atm because...

  o increasing pressure increases the amount of ammonia produced (less moles on product side of reaction)

  o the forward reaction is exothermic, so a low temperature would produce more ammonia but higher

  temperatures are used as it increases the rate of reaction
• Production & uses of NPK fertilisers

  • often farmers use manure to fertilise fuels, but formulates fertilisers are better because...

  o they are more widely available, easier to use, don’t smell and have the perfect ratios of nutrients

  • compounds of nitrogen, phosphorus and potassium are used as fertilisers to improve agricultural output

  o if plants are deficient in any of these then their growth is affected

  o NPK fertiliser use all 3
• • Industrial production of NPK fertilisers can be achieved using a variety of raw materials in several integrated processes – NPK fertilisers are formulations of various salts containing specific proportions of the elements

  • ammonia can be used to manufacture ammonium salts and nitric acid – nitrogen rich fertilisers

  o ammonia can be reacted with water and oxygen to produce nitric acid

  o ammonia and nitric acid react to produce ammonium nitrate
• o in the lab (small-scale, safe but slow)

  ▪ reactions carried out on a small scale, titration and crystallisation used

  ▪ low concentrations used so less heat is produced (safer)

  ▪ after titration, the mixture is crystalised, gives pure ammonium nitrate crystals

  o in industry

  ▪ the reaction is carried out in large vats, at high concentrations

  ▪ extremely exothermic reaction, the heat released evaporates water making the mixture produced very concentrated ammonium nitrate
• • potassium chloride, potassium sulfate and phosphate rock are obtained by mining

  o phosphate rock cannot be used as a fertiliser directly as the potassium is insoluble

  o phosphate rock is treated with...

  ▪ nitric acid (produces phosphoric acid and calcium nitrate)

  ▪ sulfuric acid (produces calcium sulphate and calcium phosphate – called single superphosphate)

  ▪ phosphoric acid (produces only calcium phosphate – called triple superphosphate)

  o to produce soluble salts that can be used as fertilisers