C10: Using resources Flashcards
What is potable water? How is it different from pure water?
Water that is safe to drink, with low levels of dissolved salts and microbes.
It is not pure water in the chemical sense because it contains dissolved substances.
What do the methods of potable water production depend on?
- Available supplies of water
- Local conditions
What is fresh water?
Water with low levels of dissolved substances, e.g. rainwater, that collects in the ground, lakes and rivers.
How is most potable water produced?
- choosing an appropriate source of fresh water
- passing the water through filter beds
- sterilising with ozone/chlorine/UV light
How is potable water sourced if supplies of fresh water are limited?
By the desalination of salty or sea water.
How is desalination of sea water carried out?
What is the disadvantage of desalination?
- By distillation.
- By processes that use membranes, such as reverse osmosis.
- These processes require large amounts of energy.
Practical
Describe in brief terms how you would test and purify seawater to make it potable.
- Test pH, neutralise if needed
- Test for sodium chloride
- Distil the water if needed and recheck for NaCl
- Retest pH
Practical: testing + purifying seawater
How would you test and correct the pH of a sample of water?
- Test the pH using a pH meter
- If below 6.5, add alkali to neutralise
- If above 8.5, add acid to neutralise
Practical: testing + purifying seawater
How would you test seawater for NaCl?
- Sodium: do a flame test on a small sample - yellow in presence of Na
- Chloride: add a few drops of dilute nitric acid and silver nitrate solution to a sample - white precipitate will form in presence of Cl-
Practical: testing + purifying seawater
How would you distil water to purify it?
- Heat the water in a flask.
- The water will evaporate, leaving any dissolved salts in the flask.
- The steam is condensed in a condenser, then collected in a beaker at the end of the condenser.
Why does sewage from domestic, industrial and agricultural sources have to be treated?
- Domestic and agricultural waste water may contain organic matter and harmful microbes.
- Industrial waste water may contain organic matter and harmful chemicals.
- Water is treated so that it can be safely returned to fresh water sources.
Describe the process of sewage treatment.
- screening and grit removal
- sedimentation to produce sewage sludge and effluent
- anaerobic digestion of sewage sludge (produces methane and fertiliser)
- aerobic biological treatment of effluent
- water containing toxic substances is treated with chemicals, UV radiation or membranes
Why is sewage treatment potentially better than desalination in areas where there is limited fresh water?
It uses less energy than desalination.
Copper ores are becoming scarce. Name 2 new ways of extracting copper from low-grade ores.
- phytomining
- bioleaching
What is phytomining?
- Uses plants to absorb metal compounds.
- These are harvested and burned to produce ash that contains metal compounds.
What is bioleaching?
A process which uses bacteria to produce leachate solutions that contain metal compounds.
Phytomining and bioleaching are both processes which produce copper compounds. How are they then processed to obtain pure copper?
Copper can be obtained from solutions of copper compounds by displacement using scrap iron, or by electrolysis.
Why are phytomining and bioleaching sustainable methods of obtaining copper?
These methods avoid traditional mining methods of digging, moving and disposing of large amounts of rock.
Life cycle assessments (LCAs) are carried out to assess the environmental impact of products. What are the stages of a product’s life cycle that need to be considered?
- extracting and processing raw materials
- manufacturing and packaging
- use and operation during its lifetime
- disposal at the end of its useful life, including transport and distribution.
Why are LCAs not purely objective processes?
Use of water, resources, energy sources and production of some types of waste can be fairly easily quantified.
But allocating numerical values to pollutant effects is less straightforward, and requires judgements on value.
How can LCAs be biased?
Selective or abbreviated LCAs can be carried out to evaluate a product, but these can be misused to reach pre-determined conclusions, e.g. to support advestising claims.
Carry out a simple LCA for plastic vs. paper shopping bags.
Some glass bottles can be reused. How are others recycled to make new glass products?
They are crushed, melted and reshaped.
How can metals be recycled?
- Melting and recasting/reforming them into different products.
- The amount of separation required depends on the material and the properties required of the final product.
- E.g. some scrap steel can be added to iron from a blast furnace, to reduce the amount of iron that needs to be extracted from iron ore.
What is corrosion?
Corrosion is the destruction of materials by chemical reactions with substances in the environment.
Give an example of corrosion and the conditions needed for this to occur.
- Rusting
- Air and water are needed for iron to rust
How can corrosion be prevented?
By applying a coating that acts as a barrier.
How is aluminium prevented from corrosion?
It has an oxide coating.
Give 4 examples of coatings which protect against corrosion.
- greasing
- painting
- electroplating
- ones which contain a more reactive metal to provide sacrificial protection
Some corrosion coatings contain a more reactive metal to provide sacrificial protection. Give an example.
Zinc is used to galvanise iron.
Most metals in everyday use are __
alloys
Bronze is an alloy of what?
Copper + tin.
Brass is an alloy of what?
Copper + zinc.
Gold used in jewelry is usually an alloy of what?
Gold, silver, copper, zinc.
How is the proportion of gold in gold alloy measured?
Using carats, 24 carat being pure gold, and 18 carat being 75% gold.
Steels are alloys of what?
Iron, specific amounts of carbon, specific amounts of other metals.
Compare the properties of high and low carbon steel.
High-carbon: strong, brittle.
Low-carbon: softer, more easily shaped.
What does stainless steel contain?
Iron, carbon, nickel + chromium.
Give 2 properties of stainless steel.
- Hard
- Resistant to corrosion
Name a property of aluminium alloys.
Low density.
Name 3 uses of bronze.
- medals
- ornaments
- statues
Name 2 uses of brass.
Used in situations where low friction is required:
- water taps
- door fittings
Name a use of aluminium alloys.
- aluminium is low density (pure aluminium too soft so alloyed)
- used in aircraft manufacturing
What type of glass is most commonly used? What is another type?
- soda-lime glass
- borosilicate glass
How is soda-lime glass made?
Heating a mixture of sand, sodium carbonate and limestone.
What is borosilicate glass made from?
Sand and boron trioxide.
Which of soda-lime and borosilicate glass melts at a higher temperature?
Borosilicate glass.
Name 2 clay ceramics.
- pottery
- bricks
How are clay ceramics made?
- shaping wet clay
- heating in a furnace
What do the properties of polymers depend on?
- the monomers they are made from
- the conditions in which they are made
Low and high density poly(ethene) are both produced from ethene. Explain how each is made and compare their properties.
- LD: moderate temperature, high pressure, catalyst. Flexible; used for bags and bottles.
- HD: lower temperature and pressure, different catalyst. More rigid; used for water tanks and drainpipes.
Compare the properties and structures of thermosoftening and thermosetting polymers.
- Thermosoftening polymers melt when they are heated.
- Contain individual polymer chains, entwined together by weak forces.
- Thermosetting polymers do not melt when they are heated - they are strong and rigid.
- Contain monomers which form cross-links between the polymer chains, holding them together in a solid structure.
How are composites made?
Most are made of two materials, one embedded in another:
- A matrix, acting as a binder, surrounds and binds together fibres or fragments of the other material.
- The embedded material is called the reinforcement.
Give 4 examples of composites.
- Fibreglass
- Carbon fibre
- Concrete
- Wood
Describe the structure, properties and usage of fibreglass.
- fibres of glass are embedded in a polymer matrix
- strong and low density
- used for skis, surfboards and boats
Describe the structure, properties and usage of carbon fibre.
- long chains of bonded carbon atoms OR carbon nanotubes embedded in a polymer matrix
- strong and light
- used in aerospace and sports car manufacturing
Describe the structure, properties and usage of concrete.
- aggregate (a material made from fragments, in this case usually sand or gravel) emdedded in a cement matrix
- very strong
- used as a building material
Describe the structure of wood.
Natural composite of cellulose fibres embedded in an organic polymer matrix.
Name 3 properties of ceramics.
- insulators of heat and electricity
- brittle
- stiff
Name 3 properties of polymers.
- insulators of heat and electricity
- can be flexible
- can be easily moulded
Name 2 applications of polymers.
- clothing
- insulators in electrical items
Name 5 general properties of metals.
- malleable
- good conductors of heat and electricity
- ductile
- shiny
- stiff
Name 3 applications of metals.
- electrical wires
- car bodywork
- cutlery
What is the Haber process?
An industrial process used to produce ammonia, which is used to make fertilisers.
What are the raw materials for the Haber process, and where are they sourced?
- Nitrogen - obtained from the air
- Hydrogen - produced by reacting methane with steam (also produces carbon dioxide)
What are the industrial conditions used in the Haber process (temperature, pressure, catalyst)?
- 450°C
- 200 atm
- Iron catalyst
Explain what happens during the Haber process.
- Purified nitrogen and hydrogen are passed over an iron catalyst at about 450°C, at a pressure of about 200 atmospheres.
- Some of the hydrogen and nitrogen reacts to form ammonia.
- The reaction is reversible, so some of the ammonia produced breaks down into nitrogen and hydrogen: nitrogen + hydrogen ⇌ ammonia
- When cooled, the ammonia liquefies and is removed.
- The remaining hydrogen and nitrogen are recycled.
In the Haber process, why is the temperature of the reaction set to 450°C?
- The forward reaction is exothermic
- So increasing the temperature means the equilibrium position shifts to the left, and away from ammonia
- Yield of ammonia is greater than that of hydrogen and nitrogen at lower temperatures
- But lower temperatures also mean a lower rate of reaction
- So it’s a trade-off, and the temperature is a comprimise of these two things
What do NPK fertilisers contain?
They are formulations containing compounds of nitrogen, phosphorus and potassium in the appropriate percentage of the elements.
How is ammonia used to produce salts for fertilisers?
- Ammonia can be used to manufacture nitric acid
- Ammonia can be reacted with acid to make ammonium salts, e.g.:
- Ammonia and nitric acid react to produce ammonium nitrate
How is the potassium used in NPK fertilisers sourced?
Potassium chloride and potassium sulfate can be mined.
How can the phosphate used in NPK fertilisers be sourced?
- Phosphate rock can be mined
- It can’t directly be used as a fertiliser (plants can’t absorb the insoluble phosphate salts in the rock)
- The rock is treated with nitric/sulfuric/phosphoric acid to produce soluble salts that can be used as fertilisers
What salt(s) is/are produced when phosphate rock is treated with nitric acid?
- phosphoric acid
- calcuim nitrate
What salt(s) is/are produced when phosphate rock is treated with sulfuric acid?
- calcium sulfate
- calcuim phosphate
What salt(s) is/are produced when phosphate rock is treated with phosphoric acid?
• calcium phosphate
