4.10 Using Resources Flashcards
Using the Earth’s resources
Humans use the Earth’s resources to provide warmth, shelter, food and transport.
Natural resources, supplemented by agriculture, provide food, timber, clothing and fuels.
Examples of natural resources are cotton, crude oil, and timber.
Some resources can be replaced by synthetic products (rubber) and others cannot. natural rubber comes from the sap of a tree, whereas synthetic rubber is made using crude oil (2 thirds of the rubber used in the world is synthetic)
Some natural resources are finite, cannot be replaced as quickly as they are being used. (fossil fuels and metals, huge amounts extracted from the world’s crust) -> we will run out of them one day, limited supply
Example of a renewable resource is wood, we can replace these resources as quickly as we use them -> will never run out
sustainable development
Chemistry plays an important role in improving agricultural and industrial processes to provide new products and sustainable development, which is
development that meets the needs of current generations without compromising the ability of future generations to meet their own needs
(we can meet our needs, without preventing future generations meeting their own)
Chemistry’s role, an example of a natural product that has been supplemented/replaced by synthetic products
Chemistry plays an important role in how we use our resources. Artificial fertilisers -> allow us to grow more food with the land available, enhances crop yields
importance of water quality for human life and define potable water
Water of appropriate quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts (sodium chloride) and microbes (bacteria), pH between 6.5 and 8.5.
Water that is safe to drink is called potable water. Potable water is not pure water in the chemical sense because it contains dissolved substances, whereas pure water just contained H20
methods to produce potable water
- depend on available supplies of water and local conditions
When is rains, water can either collect as surface water (lakes, rivers reservoirs), or as groundwater (in rocks called aquifers that trap water underground)
In the UK, rain provides water with low levels of dissolved substances (fresh water) that collects in the ground and in lakes and rivers -> good sources of fresh water
- choosing an appropriate source of fresh water (eg a river)
- > filtration -water is passed through filter beds to remove materials such as leaves and insoluble particles. Then the water is sterilised to kill microbes, in the UK we use chloride to sterilise potable water. In some parts of the world, other sterilising agents used for potable water are ozone or ultraviolet light
desalination
- however, in many places, fresh water is scarce and the only available water might be too salty -> sea water
sea water has very high levels of dissolved substances, and potable water is produced by desalination
Desalination reduces levels of dissolved substances to an acceptable level for potable water
Desalination can be done by distillation or by processes that use membranes such as reverse osmosis
- reverse osmosis -> the salty water is passed through a certain membrane that only allows water molecules to pass through, ions and larger molecules are trapped by the membrane -> separated from the water
Both of these processes require large amounts of energy, so they are very expensive, not practical fir producing large amounts of fresh water
RP8: : 1. analysing a sample of water
- Use pH meter or universal indicator to test the pH of the water. Use an appropriate colour chart and record your observations.
- Measure and record the mass of an empty evaporating basin.
- Pour 10 cm3 water into the evaporating basin and evaporate the water using a Bunsen burner until no liquid remains
- Once the evaporating basin is cool, reweigh and record the change in mass.
- Calculate the mass of dissolved solids in the water.
RP8 safety precautions
safety goggles must be worn at all times (acidic or alkaline water samples), do not ingest the water -> might be contaminated because the apparatus might not have been cleaned properly before the practical.
RP8: 2. Purifying a sample of water by distillation
- Place the water sample in a conical flask and set up the apparatus for distillation.
- Heat the water gently using a Bunsen burner until it boils. Then reduce the heat so the water boils gently.
- Collect around 1 cm depth of water in the cooled test tube, then stop turn the Bunsen burner off.
- Analyse the water you have distilled with cobalt chloride paper and determining its boiling point
How could you test to see if the distilled water contained sodium ions and chloride ions?
practical tip for distillation
Sodium ions would give a yellow colour in a flame test. Chloride ions would give a white precipitate with silver nitrate solution after a small amount of nitric acid was added.
The delivery tube must sit above the filtrate level to prevent cold water being sucked back up the delivery tube after separation, which would break the hot glass.
waste water treatment
Urban lifestyles and industrial processes produce large amounts of waste water that require treatment before being released into the environment. Sewage and agricultural waste water require removal of organic matter (From urine and faeces) and harmful microbes. Industrial (paper and chemicals) waste water may require removal of organic matter and harmful chemicals. Otherwise it would make it very polluted and pose health risks when put back into freshwater sources like rivers and lakes
agricultural systems also produce a lot of waste water, including sludge from animal farms and nutrient run-off from fields
Process of sewage treatment
- screening and grit removal - by passing through a mesh to remove large particles and grit
- sedimentation - sewage is allowed to settle in a settlement tank -> allows tiny particles to settle out from still water -> produces sewage sludge and effluent (the liquid which remains on top)
- sewage sludge is digested anaerobically by specific bacteria, releasing methane gas -> used as an energy source, the digested waste can be used as fertilisers
- the effluent contains large amounts of organic matter and harmful microbes (need to be reduced before returned to the environment)-> air is pumped into the liquid effluent , allowing aerobic bacteria to multiply. As there’s oxygen, aerobic bacteria digest om and hm
- effluent can be safely discharged into rivers or seas
compare the ease of obtaining potable water from waste water as opposed to ground or salt water
- easier and cheaper way to produce potable water is to use groundwater from aquifers
- sewage treatment to make potable water requires more purification processes (uses less energy than desalination of salty water) -> only done in places where water is scarce
- desalination requires lots of energy and is expensive -> although seawater is a plentiful raw material -> good for countries with little fresh water
alternative biological methods for extracting metals,
The Earth’s resources of metal ores are limited.
Copper ores are becoming scarce and new ways of extracting copper from low-grade ores (only contain small amount of copper -> harder to extract copper economically (cost effective) from these ores) include phytomining, and bioleaching.
phytomining
Phytomining uses plants to absorb metal compounds. The plants are grown in areas known to contain metals of interest in the soil. These plants absorb the metal compound and concentrate it in their tissue. The plants are harvested and then burned to produce ash that contains a relatively high concentration of the metal compounds from which the useful metals can be extracted by displacement reactions or electrolysis.
