C6 - Global Challenges Flashcards
what are the 3 essential elements needed by plants
- nitrogen
- phosphorus
- potassium
> plants don’t grow well if these are limited
what are some symptoms of mineral deficiencies in plants
- poor growth
- discoloured leaves
what are fertilisers
- substances that replace the essential elements used by plants as they grow
what conditions must fertilisers be in, so that plant roots can easily absorb them
- ions in water soluble form
what ions are commonly found in fertilisers containing all 3 essential elements
- Nitrogen: nitrate ions (NO 3-) and ammonium ions (NH4+)
- Phosphorous: phosphate ions (PO4 3-)
- Potassium: potassium ions (K+)
what are NPK fertilisers
- fertilisers that provide all 3 essential elements in the form of water soluble compounds
what are some examples of NPK fertilisers
- ammonium nitrate NH4NO3
- ammonium sulfate (NH4)2 SO4
- ammonium phosphate (NH4)3 PO4
- potassium nitrate KNO3
name the raw materials needed to make ammonium sulfate
- sulfur (makes sulfuric acid)
- natural gas
- air (all 3 make ammonia)
- water
> ammonia + sulfuric acid —> ammonium sulfate
name the raw materials needed to make ammonium phosphate
- phosphate rock
- sulfur —–> phosphoric acid
- natural gas
- air —–> ammonia
- water
> ammonia + phosphoric acid —> ammonium phosphate
how can potassium sulfate be made in the lab
- pour dilute potassium hydroxide into conical flask + add phenolphthalein indicator
- add dilute sulfuric acid from a burette until neutralised
- add activated charcoal to remove indicator, then filter out to remove
- warm filtrate to leave crystals behinds (don’t heat to dryness)
how can ammonium sulfate be made in the lab
- pour dilute ammonia solution into conical flask + add methyl orange indicator
- add dilute sulfuric acid from burette until neutralised
- at the end-point add a little extra ammonia solution to ensure the reaction is complete
- add activated charcoal to remove indicator + filter to remove
- warm the filtrate leaving crystals behind (don’t heat to dryness)
what is a batch process
- when you make a small amount of substance at a time and once it’s made you stop the reaction
what is a continuous process
- when large amounts of substances are made and go on continuously without the reaction being stopped
what is the Haber Process
- produces ammonia from nitrogen and hydrogen
what is the equation for the Haber process
Ns(g) + 3H2(g) <—–> 2NH3(g)
what conditions are used to carry out the Haber Process
- temp of 450 degrees Celsius
- pressure of 200 atmospheres (20 MPa)
- iron catalyst
why is the pressure in Haber process considered to be a compromise
- it’s high enough to produce a reasonable equilibrium yield
> as equilibrium shifts to the right side because there’s less moles of gas so more product - however it’s not too high for it to be hazardous and expensive
why is the temperature in Haber process considered to be a compromise
- it’s low enough for a reasonable equilibrium yield
> because forward reaction is exothermic so to counteract equilibrium shifts to the left, decreasing ammonia yield - however it’s high enough for a reasonable rate of reaction + for the catalyst to work efficiently
what are the raw materials for the Haber Process
- natural gas
- air
- steam
how is nitrogen manufactured to be used in the Haber process
- nitrogen is manufactured by the fractional distillation of liquefied air
> air is 78% nitrogen
how is hydrogen manufactured to be used in the Haber Process
- hydrogen is manufactured by reacting natural gas (mostly methane) with steam
what other conditions are chosen for Haber process
- liquefying ammonia (letting gas cool + turn to liquid)
> conc of NH3 decrease so to counteract equilibrium shifts to right to increase NH3 yield - recycling the unreacted hydrogen + nitrogen
- both of these improves the yield to around 97%
what is the contact process
- an important process in the formation of sulfuric acid
what is sulfuric acid used for
- making fertilisers
- oil refining
- metal extraction
- making paints + polymers
what are the 3 raw materials needed for making sulfuric acid
- sulfur
- air (source of oxygen)
- water
what step process is sulfuric acid synthesised in
- 3 step process
> including the contact process
what is stage 2 in the synthesis of sulfuric acid
- the contact process
> sulfur dioxide and oxygen react to produce sulfur trioxide
sulfur dioxide + oxygen —> sulfur trioxide
2SO2 + 2O2 <—> 2SO3
> energy change = -144kj/mol = exothermic
> reversible reaction because double arrow
what is stage 1 in the synthesis of sulfuric acid
- sulfur burns in air to produce sulfur dioxide
sulfur + oxygen —> sulfur dioxide
S(s) + O2(g) —> SO2(g)
> energy change = -297kj/mol = exothermic
> not reversible as single arrow
what conditions are used for the contact process (stage 2)
- pressure of 2 atmospheres (200 kPa)
- temperature of 450 degrees Celsius
- vandium oxide catalyst (V2O5)
> under these conditions equilibrium yield is around 96%
why is the pressure chosen for Contact process a compromise
- increased pressure will push equilibrium to the right with less moles of gas
> however, in this reaction equilibrium is already so far to the right that we don’t need to spend more money on increasing the pressure
> the pressure is enough
why is the temperature a compromise for the contact process
- forward reaction is exothermic so to oppose the change the equilibrium will shift in the endothermic direction
> the temperature chosen is a compromise as it’s low enough for a reasonable equilibrium yield but it’s high enough for a reasonable rate of reaction + for catalyst to work
what are the hazards in stage 3 of the synthesis of sulfuric acid + how can they be controlled
- reaction between sulfur trioxide + water = very exothermic + produces hazardous acidic mist
- so stage 3 is carried out in 2 steps:
> 1. sulfur trioxide reacts with concentrated sulfuric acid to make a compound called oleum
H2SO4 + SO3 –> H2S2O7
> 2. the oleum is added to water to produce sulfuric acid as a final product
H2S2O7 + H20 –> 2H2SO4
what is stage 3 in the synthesis of sulfuric acid
- sulfur trioxide is converted into sulfuric acid
> sulfur trioxide + water —> sulfuric acid
SO3 + H2O —> H2SO4
> not reversible
what is an ore
- a rock or mineral that contains enough metal (or metal compound) to make it economical to extract the metal
give examples of some ores + metal compounds found in the ore
- malachite = copper carbonate
- bauxite = aluminium oxide
- haematite = iron (III) oxide
what extraction methods are there to extract metals from their ores
- essentially all metals could be extracted using electrolysis but electricity is expensive
> instead, metals less reactive than carbon can be extracted by heating their compounds with carbon / carbon monoxide
> as carbon (more reactive) can displace the oxygen
how is copper extracted from an ore
copper can be extracted from copper(II) sulfide in 2 stages:
- stage 1- first the copper(II) sulfide is ‘roasted’ in air
> copper(II) sulfide + oxygen —> copper(II) oxide + sulfur dioxide
2CuS(s) + 3O2(g) —> 2CuO(s) + 2SO2 (g)
- stage 2 - the copper(II) oxide is heated with carbon
> copper(II) oxide + carbon —> copper + carbon dioxide
2CuO(s) + C(s) —> 2Cu(s) + CO2(g)
what is stage 2 in copper extraction from ore, an example of
- redox reaction
> copper(II) oxide loses oxygen (reduced)
> carbon gains oxygen (oxidised)
what other methods can be used to reduce Copper(II) oxide to copper
- by heating it with methane / hydrogen
> copper oxide + hydrogen —> copper + water
> copper oxide + methane (CH4) —> copper + carbon dioxide + water
> methane contains carbon + hydrogen
what are the unreactive metals
- silver
- gold
- platinum
what are native elements
- elements found in pure form in the earth’s crust
what is a blast furnace used for
- to extract iron from it’s core
what raw materials are added to the top of the blast furnace
- iron ore (haematite) - contains iron(III) oxide
- coke - mostly carbon + made by heating coal in absence of air
- limestone - mostly calcium carbonate - removes impurities
> additionally, hot air is forced in at the bottom of the blast furnace
what is a reducing agent
- a substance which causes something to be reduced so they lose oxygen
> reducing agents get oxidised as they gin oxygen
what is the main reducing agent in the blast furnace
- carbon monoxide
> formed when coke reacts with carbon dioxide
what is stage 1 in the extraction of iron in a blast furnace
- coke burns in the hot air making carbon dioxide
C(s) + O2(g) —> CO2(g)
what is stage 2 in the extraction of iron in a blast furnace
- more coke reduces the carbon dioxide, making carbon monoxide
C(s) + CO2(g) —> 2CO(g)
what happens in the blast furnace once iron(III) oxide gets reduced to iron
- the molten iron trickles downwards in the blast furnace
> however it contains sandy impurities from iron ore
> this can be removed using limestone (calcium carbonate)
what is stage 3 in the extraction of iron in the blast furnace
- carbon monoxide reduces iron(III) oxide to iron at around 1500 degrees Celsius
3CO(g) + Fe2O3(s) —> 3CO2(g) + 2FE(l)
what happens in stage 4 in the extraction of iron in the blast furnace
- calcium carbonate decomposes in high temperatures forming calcium oxide and carbon dioxide
CaCO2(s) —> CaO(s) + CO2(g)
what happens in stage 5 in the extraction of iron in the blast furnace
- the calcium oxide formed reacts with silica from the sandy impurities to form calcium silicate (slag)
CaO(s) + SiO2(g) —> CaSiO3(l)
what is the final steps of the extracting iron from a blast furnace after all 5 stages
- molten calcium silicate (called slag) floats on molten iron
- both iron + slag are removed separately at the bottom of the blast furnace
write balanced equations + small explanations for all the reactions taking place in the blast furnace when extracting iron
- C(s) + O2(g) —> CO2(g)
> coke burns in air making carbon dioxide - C(s) + CO2(g) —> 2CO(g)
> more coke reduces carbon dioxide to carbon monoxide - 3CO(g) + Fe2O3(s) —> 3CO2(g) + 2Fe(l)
> carbon monoxide reduces iron(III) oxide to iron at around 1500 degrees Celsius - CaCO3(s) —> CaO(s) + CO2(g)
> calcium carbonate decomposes in high temperatures forming calcium oxide + carbon dioxide - CaO(s) + SiO2(g) —> CaSiO3(l)
> calcium oxide formed, reacts with silica from sandy impurities to form calcium silicate (slag)
what are some uses of aluminium
- can be used in pans, drink cans and cars
- aluminium alloys have low density but are very strong so can be used in bicycles + aeroplanes
what does aluminium naturally exist as
- aluminium oxide
Al2O3
what ore is aluminum found in
- bauxite
what method is used to extract aluminium from it’s ore + why
- electrolysis
- because aluminium is more reactive than carbon so must be extracted through electrolysis
where is the molten mixture of aluminium oxide + cryolite contained
- huge electrolysis cell
> made from steel, lined with graphite
> graphite lining acts as the cathode
> huge graphite blocks act as anode
electrolysis only works if the compound is ____ or ______
- molten
- in solution
what are problems with the electrolysis of just aluminium oxide
- aluminium oxide is insoluble in water + has a very high melting point (2050)
> it would be very expensive to heat it to this temp
how can you reduce the melting point of aluminium oxide in order to carry out electrolysis
- by adding an ionic compound called cryolite
> cryolite has a much lower melting point
> this allows electrolysis to happen at about 950
during electrolysis of aluminium oxide, what is produced at the anode + cathode + give half equations
- aluminium is produced at the cathode where it gains electrons (reduction)
Al3+ + 3e- —> Al - oxygen is produced at the anode where it loses electrons (oxidation)
2O2- —> O2 + 4e-
during the electrolysis of aluminium oxide, what does the oxygen react with
- the oxygen reacts with the hot graphite anodes, making carbon dioxide
what is the difference between high grade ore and low grade ore
- high grade ore = high metal content
- low grade ore = low metal content
how can bacteria produce sulfuric acid
- by oxidising iron(II) ions + sulfide ions
> the sulfuric acid forms in the presence of water + oxygen
what are the 2 biological methods of metal extraction
- bioleaching
- phytoextraction
outline how bioleaching works
- bacteria can be used to produce sulfuric acid by oxidising iron(II) ions + sulfide ions
> in the process, sulfuric acid forms in the presence of water + oxygen - the sulfuric acid produced can break down copper sulfide ores (and other metals) releasing copper(II) ions along with other metal ions
what are the advantages of bioleaching
- cheaper than traditional mining
- allows metals to be extracted from low grade ores
- bacteria occur naturally + don’t need any special treatment
- doesn’t release harmful sulfur dioxide into atmosphere
what are the disadvantages of bioleaching
- very slow process
- toxic substances produced sometimes
- care must be taken to ensure toxic substances + sulfuric acid don’t escape into water supplies + soil
outline how phytoextractions works
- plants absorb dissolved ions through their roots
> some plants are particularly good at absorbing certain metal ions, which then accumulate in their roots, shoots and leaves - a crop is planted in soil containing low-grade ore or mine waste
> a ‘complexing agent’ may be added so plants can absorb the metal ions more easily - the plants are then harvested + burnt to ash - leaving behind a high concentration of the metal remaining
> the metal can be extracted in normal way with any high grade ore
what are advantages of phytoextraction
- cheaper than traditional mining + processing
- produces less waste
- involves smaller energy transfers
- closer to being a carbon neutral activity that can contribute to sustainable development
- CO2 produced is absorbed by plants for photosynthesis as they grow
- burning plants can generate electricity
what are disadvantages of phytoextraction
- slow
- crops may need replanting + harvesting for several years before the available metal is removed from soil
- burning plants release CO2
what are alloys
- mixtures of two or more elements
> of which at least one is a metal
what are 5 important alloys
- steel
- duralumin
- solder
- brass
- bronze
what main metal(s) are present in steel
- iron
what main metal(s) are present in duralumin
- aluminium
- copper
what main metal(s) are present in solder
- tin
- copper
what main metal(s) are present in brass
- copper
- zinc
what main metal(s) are present in bronze
- copper
- tin
what are some uses of steel
- buildings
- bridges
- cars
what are some uses of duralumin
- aircraft parts
what are some uses of solder
- joining electrical components + copper pipes
what are some uses of brass
- musical instruments
- coins
why is solder’s property useful
- the low melting point makes the metal useful for joining electrical components together without damaging them
what are some uses of bronze
- bells
- ship propellers
what key properties does bronze have + why are they useful
- resists corrosion
- stronger + harder than copper
> makes it useful for ship propellers
> also used to make bells + metal artwork
what are some useful properties of steel
- high tensile strength
- ductile
how does solder differ to pure tin + copper
- solder have low melting points (227 C)
> tin has 232 C
> copper has 1085 C
what key properties does brass have + why are they useful
- good electrical conductor
- resists corrosion - doesn’t react easily with water / air
> these properties make brass useful for making pins for electrical plugs
what is corrosion
- the reaction of metal with substances in its surroundings such as air or water
what metals don’t corrode
- very unreactive metals such as gold or platinum
does iron corrode
- yes
> when it corrodes it’s called rusting
what type of reaction is rusting
- redox reaction
> iron is oxidised to hydrated iron(III) oxide
iron + water + oxygen —> hydrated iron(III) oxide
does silver corrode
- doesn’t easily react with oxygen in air / water
> but corrodes in presence of hydrogen sulfide to produce a thin layer of black silver sulfide
what is rusting
- the corrosion of iron
how can prevent oxygen + water from reaching the surface of metals
- painting the metal
- coating with oil / grease / plastic
- plating with zinc (galvanising)
- plating with tin
what is the word equation for the making of rust
iron + oxygen + water —> hydrated iron(III) oxide
what is sacrificial protection
- when a more reactive metal than iron is in contact with the less reactive metal
> the metal ‘sacrifices’ itself to protect the less reactive metal (iron / steel)
how does sacrificial protection work
- the more reactive metal is in contact with less reactive metal
- more reactive metal corrodes first + protects the less reactive metal + in a way ‘sacrifices’ itself
> overtime the metal plates corrode away and will need replacing
what metals are commonly used for sacrificial protection
- metals more reactive than iron
> such as magnesium / zinc
what is metal plating
- a thin layer of metal can be plated over a structure of iron/steel, thus creating a protective layer between the air/water and the metal
> creates a physical barrier preventing corrosion
what is galvanising + how does it prevent corrosion
- galvanising involves dipping the metal into molten zinc + once cooled and solidified the layer of zinc does 2 things
> stops air/water reaching iron/steel below
> acts as a sacrificial metals so the object is protected, even if zinc is damaged
what is tin plating
- tin plating involves electroplating the steel object with tin / dipping it into molten tin
> e.g. inside steel food cans
what are ceramics + examples
- hard, non-metallic materials
> e.g. brick, china, porcelain, glass
how is glass made
- by melting sand + allowing it to cool and solidify
what are some typical properties of ceramics + why do they have them
- high melting points
- hard + stiff but brittle
- poor conductors of electricity + heat
> all of this is because ceramics contain metals + non-metals which combine to form giant covalent structures giving them these properties
what is a disadvantage of tin plating
- tin is less reactive than iron
> so if damaged, the steel will act as a sacrificial metal for the tin + speeds up rusting even fasting than normal
why are ceramics unreactive
- because the compounds in ceramics are mostly oxides
describe the structure of glass
- has irregular giant structure
- without crystals
- usually transparent
how are other ceramics (not glass) made
- by heating clay to very high temperatures
> tiny crystals form which are joined by glass
why are china + porcelain usually coated in glaze
- glaze forms a smooth, hard & waterproof surface
what is a composite material
- a material made from 2 or more materials combined, each with different properties
what useful properties do cotton-polyester have + how do they differ to cotton and polyester individually
- cotton-polyester is made by weaving cotton thread with polyester fibre, an artificial polymer
> it’s comfortable, but harder wearing than cotton, and easier to wash and dry - cotton on the other hand is lightweight and comfortable to wear but not very hardwearing
what does fibreglass consist of + what is it used for
- fibreglass consist of glass fibres in resin
- used for:
> canoes
> boats
> surfboards
what does carbon fibre consist of + what is it used for
- carbon fibre consists of carbon fibres in resin
- used for:
> sports equipment
> racing cars
> aircraft part - it’s more expensive than fibreglass
how do properties of steel-reinforced concrete compare to concrete + why is this useful
- steel-reinforced concrete has high compressive strength + high tensile strength
- concrete has high compressive strength + but low tensile strength
> steel-reinforced concrete creates a composite material which is strong because it has high composite + tensile strength so wont squash or crack/break
why do we recycle materials
- to converse raw materials (e.g. metals)
- reduce waste
- avoid filling landfill sites
- conserve energy resources (e.g. from fossil fuels)
- reduce the release of harmful substances into atmosphere
- avoid waste polluting oceans + seas
what factors need to be considered when deciding if a product should be recycled
- how easily the waste can be collected + sorted
- cost of recycling compared to disposal in landfill or by incineration (burning)
- amount + type of by-product released by recycling
- amount of energy involved at each stage
what is a life-cycle assessment
- LCA is a ‘cradle-to-grave’ analysis of the impact of making, using, and disposing of a manufactured product
what should LCA’s include data about
- sustainability, including raw materials + energy
- environmental impact, including waste products + pollution
- lifespan of the product + whether any of it can be recycled
- disposal, including how easily the materials decompose
how are metals recycled
- metals are melted + moulded into new blocks called ingots
what are the stages in a products life
- extracting + processing raw materials
- manufacturing + packaging
- use + operation during its lifetime
- disposal at the end of its useful life, including transport + distribution
why are life-cycle assessments carried out
- to identify the stages that could be improved
- to find alternative materials that might do the same job
how is paper recycled
- paper is mixed with water + cleaned + rolled + heated to make new paper
how is glass recycled
- glass is melted + moulded into new glass objects
how are polymers recycled
- polymers like plastic are melted + formed into new objects
what 3 main substances make up the earth’s atmosphere
- nitrogen 78%
- oxygen 21%
- argon 0.9%
> trace amounts of other gas e.g. carbon dioxide (0.04%) + water vapour
where did the earth’s early atmosphere come from
- substances released by volcanic activities
how old is the earth
4.54 billion yeas old
what substances did the volcanoes release in early atmosphere
- huge volumes of water vapour + carbon dioxide
how did oceans form
- as the earth cooled, the water vapour condensed to form oceans, leaving an atmosphere of mostly carbon dioxide
after the oceans were formed what did the earth’s atmosphere contain
- mostly carbon dioxide
> contained small amounts of other gases like ammonia, methane and nitrogen
> but little or no oxygen
how did oxygen levels increase in the atmosphere
- oxygen produced from photosynthesis helped remove any ammonia + methane in atmosphere by reacting with it
- oxygen also reacted with metals, forming metal oxides
> after a while, as most metals became oxidised, free oxygen began to accumulate in the atmosphere
why has the atmosphere changed over time - increased levels of oxygen but decreased levels of carbon dioxide
- through photosynthesis
> plants + algae took in carbon dioxide from atmosphere and released oxygen
how was the ozone layer created
- eventually so much oxygen was produced that a protective layer began to form around the planet
> this is now what we call the ozone layer - O3
> ozone layer protected earth from UV rays
> this led to evolution and growth of animals
what are pollutants
- substances which are released into the environment that may harm living things
- where are atmospheric pollutants released + what are they caused by
- into the air
> many are released as a result of burning fossil fuels
> they include carbon monoxide,
particulates, nitrogen oxides, sulfur
dioxide
how is carbon monoxide produced
- during incomplete combustion when not enough oxygen is present:
hydrocarbon + not enough O2 (burn to produce) carbon monoxide fine particles
what is carbon monoxide + what happens when inhaled
- a toxic colourless gas, no smell / test
> when breathed in it combines with haemoglobin which reduces the amount of oxygen that the bloodstream can carry
> Co poisoning can cause drowsiness, difficulty breathing + even death
in what circumstances is CO produced
- during incomplete combustion of fuels containing carbon
> when coal, wood, or natural gas are burned in poor supply of air
> in vehicle engines
what safety measures are taken to ensure CO can be detected
- installing carbon monoxide detectors in homes etc
what are particulates + how are they produced
- particulates are small particles
- they are produced in industrial process such as metal extraction
> they are also produced during incomplete combustion + in vehicle engines
what happens when particulates are inhaled
- smallest particulates settle deep in the lungs when breathed in
> causes diseases such as bronchitis + other breathing problems + increases chance of heart disease
why does sulfur produce problems as a pollutant
- when fuels are burnt, sulfur impurities are released
> these react with oxygen to form sulfur dioxide gas - sulfur dioxide mixes with water in clouds, forming dilute sulfuric acid
> when this acid rain falls it damages buildings + kills trees + living things
how can you prevent acid rain
- remove sulfur impurities from fuel before you burn it
- sulfur gas can be removed from factories + chimneys using calcium oxide which neutralises the acidic oxides produced
why does nitrogen cause problems as a pollutant
- only at high temps in vehicle engines, nitrogen in the air react with oxygen gas producing nitrogen oxides
> nitrogen oxides are toxic + trigger asthma attacks - can also lead to formation of acid rain
why do acidic oxides cause problems
- they can cause acid rain
> acid rain destroys buildings especially limestone
+ can kill living thins in rivers + lakes and can kill trees
what is the greenhouse effect
- when greenhouse gases such as CO2 + methane absorb infrared radiation radiated by Earth’s surface, then emit it in all directions
> this keeps the earth + its atmosphere warm enough for living things to exist
how is carbon dioxide (greenhouse gas) released into the atmosphere
- by combustion of fossil fuels
how is methane (greenhouse gas) released into the atmosphere
- from rice paddy fields
- cattle
- landfill waste sites
- use of natura; gas
what is the enhanced greenhouse effect + what does it lead to
- the release of additional greenhouse gases by human (anthropogenic) activities has potential to cause an enhanced greenhouse effect which increases the temperature of the earths atmosphere
> this global waring leads to melting ice caps + rising sea levels + climate change
> climate change brings altered weather patterns, causing flooding + problems with farming + disease control
what does global warming lead to
- melting ice caps
- rising sea levels
- climate change
what does climate change bring about
- altered weather patterns causing:
> flooding
> problems with farming + disease control
how can greenhouse gas emission be reduced into the atmosphere
- reducing consumption of fossil fuels, by using biofuels
- using renewable energy resources such as wind + solar energy to generate electricity
- stopping CO2 escaping when fuels are used by using carbon capture
> such steps are expensive but so are steps to protect against the effects of global warming
> e.g. flood barriers, planting diff crops, designing buildings to withstand high winds
how is carbon capture used to stop CO2 escaping when fuels are used
- CO2 produced in power stations can be pumped deep underground into porous rocks + trapped there
> this process is expensive + companies would need to increase cost of electricity o offset this extra cost
how does build up of greenhouse gases lead to global warming
- more IR radiation gets trapped than usual and as a result the energy leads to an increase in global temperatures - also known as global warming
what is potable water
- water which is safe for drinking
what is a reservoir
- an enlarged natural or artificial lake used as a source of water supply
what is an aquifer
- layer of rock which stores water underground
what is desalination
- the process of removing dissolved salts from water
where does drinking water originally come from
- water stored in lakes, reservoirs or aquifers
> it may have also come from rivers or waste water
water from all the sources (lakes, reservoirs, aquifers) contain microorganism and many different substances such as:
- insoluble materials like leaves + particles from rocks and soil
- soluble substances, including salts + pollutants such as pesticides + fertilisers
how can we produce potable water
- 2 main approaches depending on what type of water we’re dealing with
> fresh water
> salt water
how is freshwater treated to produce potable water
- there are a few steps:
1. screening - removal of large insoluble objects
2. settlement, coagulation, sedimentation - removal of smaller insoluble substances
3. filtration - removal of any remaining insoluble substances
4. chlorination - to kill any bacteria
5. final checks - to ensure pH is neutral + add any useful chemicals like fluoride ions
how is salt water treated to produce potable water
- seawater contains very high concentrations of dissolved salts
> to make this water potable, the salt must be removed, in a process called desalination - for small scale desalination, we use a process called ‘reverse osmosis’ which uses special ‘ultrafilters’ to filter out the salts
> for large scale desalination, simple distillation is used
