C10 (resources) Flashcards
(128 cards)
1
Q
what do humans use resources for?
A
- warmth
- shelter
- food
- transport
2
Q
give examples of resources produced by agriculture:
A
- cotton, from a plant. modern agriculture allows us to grow enough to meet the needs of the planet
- planting trees, which can be used for timber/fuels. e.g. many power stations run on bio-fuels such as wood chips
3
Q
give an example of how we’ve replaced natural resources with a synthetic alternative:
A
- rubber
- natural rubber comes from the sap of a tree
- synthetic rubber is produced using crude oil, and about 2/3 of the rubber used globally is synthetic
4
Q
give examples of finite resources:
A
- fossil fuels (we use millions of kilograms every day)
- metal (huge amounts are extracted from the Earth’s crust)
5
Q
what does it mean to be sustainable?
A
meeting our needs without preventing future generations from meeting theirs
6
Q
how does chemistry play an important role in our use of resources?
A
- artificial fertilisers allow us to grow more food with the land available
- provides water that is safe to drink
- processes such as phytomining and bioleaching help us to extract metals more efficiently
7
Q
what does drinking water require in order to be safe for human consumption?
A
- sufficiently low levels of dissolved salts (e.g. sodium chloride, magnesium, calcium ions)
- pH between 6.5 and 8.5
- cannot have high levels of microbes (e.g. bacteria)
8
Q
what is potable water?
A
water that is safe to drink
9
Q
what is the difference between potable and pure water?
A
- pure water in the chemical sense contains no dissolved substances at all
- potable water does, just in quite small amounts, still making it impure
10
Q
where is most of our freshwater provided from in the UK?
A
rainwater, as it contains low levels of dissolved substances (dissolves gases as it falls through the air)
- this water collects in the ground in aquifers, and in lakes, rivers, and reservoirs
- it is freshwater, and technically potable, but we still treat it to ensure it’s completely safe to drink
11
Q
what is the difference between surface water and groundwater?
A
- surface water includes bodies of water exposed at the surface (e.g. lakes, rivers, reservoirs)
- ## benefits include that it’s easy to access and is replaced frequently by the rain. however, if it’s hot and sunny, it can dry up due to evaporation
- groundwater includes sources found underground (e.g. aquifers)
12
Q
what is an aquifer?
A
an area of permeable rock underground that traps water
13
Q
how do we produce potable water?
DESCRIBE THE FILTRATION STAGE
A
- screening removes large solid particles i.e. twigs and leaves by passing the water through filter beds and a wire mesh
- adding aluminium sulfate clumps together the remaining solids so that they also sink to the bottom and all solids are removed
14
Q
how do we produce potable water?
DESCRIBE THE CHEMICAL TREATMENT STAGE
A
- bubble chlorine gas through it and use ozone and UV light to get rid of harmful bacteria/microbes
- test the water and balance the pH, which needs to be at pH 7 for safe consumption
- the water is stored in large tanks and is released into homes, businesses and factories
15
Q
what do countries with no fresh water access do to get potable water?
A
- in the UK we have a lot of fresh water access, with low levels of dissolved minerals
- in many places, fresh water is scarce, and the only available water may be too salty and contain too many dissolved minerals to drink (e.g. sea water)
- potable water is produced by desalination
16
Q
what is desalination?
A
reduces the levels of dissolved minerals (salt) down to an acceptable level for potable water
17
Q
describe reverse osmosis:
A
apply pressure to salt water to push it through a semi-permeable membrane, where the water gets through but the salt doesn’t
18
Q
describe the method for distillation:
A
- boil the water at 100 degrees celsius, so it vapourises
- the vapour rises, and condenses into a separate chamber to the salt
- the salt has a different boiling/melting point, so it doesn’t evaporate with it
19
Q
describe some methods of desalination:
A
- distillation
- reverse osmosis, by passing the water through membranes
20
Q
what are the disadvantages of the methods of desalination?
A
require very large amounts of energy, which is expensive and quite impractical for producing large quantities of water
- not done here in the UK, but done in the Middle East with little access to freshwater. they have more money (from their oil), and more solar energy to power the process
21
Q
what is negative about waste water, and how can we fix it?
A
- contains many organic molecules (e.g. urine, faeces). also contains harmful microorganisms (e.g. bacteria)
- industrial wastewater in addition to this contains harmful chemicals, which require extra steps to be removed
- the water must be treated before being released back into the environment or being reused
22
Q
what are the three main sources of wastewater?
A
domestic (household): showers, sinks, toilets. this water heads to sewers and then sewage treatment plants
agriculture: nutrient run-off, animal waste
industrial (factories): chemicals
23
Q
describe the stages of waste water treatment:
A
- the sewage is screened by passing through a mesh, removing solids and pieces of grit
- the sewage can settle in large sedimentation/settlement tanks, producing a liquid effluent at the top and a semi-solid sludge which sinks
- the sludge tank is sealed. this sludge is taken away and digested by anaerobic bacteria, and this produces biogas (methane) which can be burned for electricity or as bio-fuels. the digested sludge forms sludge cakes can be used as fertilisers for farming
- the liquid effluent still contains organic molecules and harmful microorganisms. air is bubbled through the liquid, allowing aerobic bacteria to multiply, which digest the molecules and microorganisms
- the liquid effluent can be safely discharged into nearby rivers/the sea
24
Q
what happens to water used in industry?
A
- a lot of water is used in industry, e.g. in making paper and chemicals
- when this water is treated, any harmful chemicals and organic matter must first be removed, by adding chemicals or through the use of ultraviolet radiation
- after this, the water can then safely enter general sewage treatment
25
describe the method of producing potable water from groundwater aquifers:
this is usually safe to drink, once treated with chlorine
- however, aquifers can sometimes by polluted e.g. with fertilisers from farms, so the water from aquifers must be tested carefully
26
describe producing potable water directly from waste water (e.g. sewage):
this is only done in places where water is scarce, as it takes many purification steps
27
describe producing potable water from salt water:
must be desalinated. this requires a lot of energy and is expensive
28
how are most metals found in the Earth's crust?
already reacted with other elements, e.g. oxygen
29
how is copper used?
- very important
- used in electronic equipment, e.g. phones, electrical wiring, plumbing pipes
- however, it's becoming scarce, as it's a finite resource
30
how is copper typically extracted?
- through mining, melting, and electrolysis
- energy is required, the machinery is expensive
- huge environmental impact on biodiversity, due to deforestation
- CO2 emissions
31
what is a metal ore?
a compound that contains enough metal to make it economical (cost-effective) to extract the metal
32
what are low grade ores?
ores that contain a very small amount of the desired metal, meaning it's harder to extract the metal economically from these ores
33
describe the method of phytomining:
1. plants are grown on the land (e.g. industrial waste sites) containing the copper compound, usually in the form of low grade ores
2. the plants' roots absorb the copper compound, and concentrate it in their tissue, through translocation
3. the plants are then harvested and burned. the copper from the leaves reacts with oxygen in the air to form a copper oxide, collect the ash
4. react the ash with sulfuric acid to get copper sulfate
5. electrolyse it, extract the copper
34
what are the pros and cons of phytomining?
pros:
- can obtain copper in areas with low grade copper ores
- better than deforestation of massive rainforests for mining (less air pollution)
cons:
- energy is required in electrolysis, costly
- expensive to obtain sulfuric acid
- burning the plants releases CO2
- slower process
35
describe the method of bioleaching:
1. bacteria are mixed with the low grade ore
2. the bacteria carry out chemical reactions and produce a solution called the leachate (a liquid that has passed through an organism), containing the metal compound we want
36
what are the pros and cons of bioleaching?
pros:
- cheap, as it's simply
- environmentally friendly, unlike smelting (traditional mining) which produces carbon and sulfur
- can be used in low grade ores when high grade ores are limited in availability
cons:
- very slow process
- efficiency in which the bacteria converts the copper ore into a copper metal is very low, so lots of waste is produced
37
how could we extract copper from a copper ore/compound?
- we can displace the copper using iron, as iron is more reactive than copper. we usually use scrap iron as it's cheap
- we can also extract the copper using electrolysis
38
what are the positives of phytomining and bioleaching?
- allow us to economically extract metal from low grade ores. this is important as the resources of metal ores are limited
- do not involve digging, transporting and disposing of large amounts of rock, unlike in traditional mining
39
what is a life-cycle assessment?
attempts to put a number on the environmental impact of a product
40
what are the 4 main stages when carrying out the life cycle assessment of a product?
- assess the environmental impact of extracting and processing the raw materials
- manufacturing the product and its packaging
- using the product during its lifetime
- disposing the product at the end of its life
41
describe stage 1 of the life cycle assessment:
all the raw materials we need come from the Earth's crust, atmosphere, oceans, or living organisms. obtaining these materials has an impact on the environment, e.g.
- using up limited resources such as ores and crude oil
- damaging habitats through quarrying, mining, or felling trees
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- processing these materials can also indirectly impact the environment as huge amounts of energy are required (e.g. when extracting metals from their ores, or through fractional distillation)
- pollutants can also be released
42
describe stage 2 of the life cycle assessment:
1. energy use
2. pollution, e.g. carbon monoxide, hydrogen chloride
3. production of waste products: sometimes they can be used as raw materials for something else, but are usually useless and must be disposed of at landfills
43
describe stage 3 of the life cycle assessment:
1. how much damage it does during its lifetime (e.g. how polluting driving a car is, or the run-off from using fertiliser)
2. how long the product is used for (e.g. bags for life vs single use paper bag)
44
describe stage 4 of the life cycle assessment:
- using up land for landfill sites that could have been used for nature
- whether any of the product can be recycled or reused
- the harmful chemicals contained must be disposed of carefully, and this may require a lot of energy (e.g. harmful chemicals can seep out from landfill sites into the surrounding ecosystem)
- it also takes energy to transport used products for disposal (e.g. to landfill/recycling centre)
- burning the waste products can release pollutants into the atmosphere
45
describe the formation of plastics:
- the oil must be extracted from the ground then transported to oil refineries
- the hydrocarbons must be separated then cracked
- the polymer must be produced
- all of these processes take a lot of energy, which is generated by burning fossil fuels, leading to climate change
46
describe the extraction of metals:
the ore must be dug out of the mine and transported for processing. the metal must then be extracted from the ore and this can produce large amounts of toxic waste products
47
compare stage 1of the life cycle assessments of a paper vs plastic bag:
- plastic bags are produced using chemicals from crude oil. paper bags are made from wood from trees
- crude oil is a non-renewable source, must also be separated using fractional distillation (energy) . trees are renewable, as we can simply plant more
- extracting crude oil can be harmful to habitats, e.g. an oil leak. felling trees for wood is also extremely destructive to habitats such as forests
48
compare stage 2 of the life cycle assessments of a paper vs plastic bag:
- to manufacture plastic bags, the hydrocarbons from fractional distillation must be cracked to make alkenes. these can undergo polymerisation
- for paper bags, the timber must be pulped (broken up into little pieces then soaked). this produces a lot of energy and waste
49
compare stage 3 and 4 of the life cycle assessments of a paper vs plastic bag:
- plastic shopping bags are strong, and are often reused as bin liners. paper bags aren't as strong, and tend to tear - they're often used only once before being thrown away
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- both plastic and paper bags must be transported either to recycling centres or to landfills
- paper bags are often heavier than plastic bags, requiring more energy to transport
- plastic is non-biodegradable (not broken down by microorganisms), so remain in the environment for a long time. they take up space in landfill and get into the wild and harm animals
- paper breaks down quickly (biodegradable), especially if it's wet. they're also non-toxic
50
what are the issues with life cycle assessments?
- we can measure the use of water, energy, and the production of waste products. we cannot always be certain of how damaging these are to the environment (e.g. making products usually involves loads of different steps which are difficult to quantify). in some cases, we must make estimates or value judgements, which aren't always accurate
- difficult to assess the harm of each step: which is worse, harm to humans or to the environment?
- they can also be easily manipulated biased (e.g. to support claims by advertisers companies, giving the company positive advertisement). this is typically hard to notice, as the calculations are so complex
51
what objects are formed from raw materials?
- glass
- metal
- building materials
- plastic
- clay ceramics
52
how are raw materials obtained?
through quarrying/mining, which is harmful to the environment
- quarrying produces a lot of dust, destroying habitats
- mining releases harmful chemicals into the environment
also takes a lot of energy to turn these raw materials into useful products, and this energy comes from limited resources, e.g. fossil fuels
53
how can we reduce our need for raw materials/resources?
recycle/reuse products, saving energy and limited resources. also reduces the amount of waste produced and have a less harmful effect on the environment
54
what is sustainable development?
an approach to human and economic development
- must meet the needs of the current generations
- without damaging the lives of future generations
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don't:
- use up all of the limited resources
- damage the environment (e.g. letting sewage wash into a river, cutting down rainforests to provide space for agriculture)
- increase global warming
55
define reuse:
lengthening the life of an item by using it for a different purpose
56
how can the use of renewable resources lead to sustainable development?
make products out of wood, instead of plastic. we can grow more trees, but plastic must come from crude oil, which is a finite resource
57
evaluate the costs of recycling:
less expensive to recycle resources than it is to make new resources. however, it still costs money to transport, sort, and process materials
58
describe making the manufacturing process more efficient:
- despite using renewable resources, a lot of energy may still be used in the manufacturing process, which comes from burning fossil fuels, which increases global warming (not sustainable)
- instead, we can make processes more efficient (only needing a tiny amount of oil to make a plastic product), or reducing the energy required for a process (using a catalyst, using the optimum temperatures and pressures)
59
describe the slogan: 'reduce, reuse, recycle'
- helps to cut down on the amount of waste produced, and on the amount of products/services used
- REDUCE the amount of waste produced
- REUSE items as much as possible before replacing them, reducing the amount of new material required to be created
- RECYCLE items wherever possible, so they don't go to landfill and release toxic chemicals into the environment, and don't product CO2 when burnt in an incinerator
60
how can glass bottles be recycled?
- can be recycled
- the bits are separated into colour and type
- can be crushed/melted and reshaped to make different glass products
- these new products can be the same, or completely different (e.g. insulating glass wool, used for wall insulation in houses)
- reduces the space needed in landfills, as it takes up to 4,000 years to decompose
61
what can plastic bottles be recycled into?
fleece jackets, carpet
62
how do we recycle metals?
melt them and recast them into different products (e.g. ingots), however metals must be separated into their different elements before being recycled, and that depends on the desired properties of the final product
- saves energy, as no mining/extraction is required, preserving precious natural resources like coal/iron ore
- the combustion of coal is also a contributor to climate change
63
when do we mix metals for recycling?
we can add scrap steel (containing iron) to pure iron, reducing the amount of pure iron we must extract from the ground
64
how can we promote recycling?
- offer rewards: however, this simply promotes more consumption, as they don't award you for reduced consumption
- educate the community and schools about recycling and the environment
65
what are the pros and cons of reducing our waste?
pros:
- reduces methane (waste decays anaerobically) from landfills
- requires less energy compared to creating new materials (less CO2 emissions, due to burning coal)
cons:
- difficult to quickly switch to a reduced, less luxurious lifestyle
66
what are the pros and cons of reusing products?
pros:
- conserves valuable resources
- causes less pollution than making new products from new materials
cons:
- the quality of the product will decrease over several rounds of reuse
67
what are the pros and cons of recycling products?
pros:
- less energy to recycle than to extract raw materials
- it gives the product a USP, meaning people are more willing to buy the product
cons:
- may reduce the quality of the finished product
- expensive and difficult process, as it must be sorted and processed
68
define corrosion:
the slow destruction of materials by chemical reactions with substances in the environment
69
why must we prevent corrosion?
- so the material lasts longer
- so it has structural stability
- so it looks more aesthetically pleasing
- to keep its electrical conductivity high
- otherwise we'd be unable to recycle it
70
describe rusting:
only applies to iron, and alloys of iron such as steel
- iron reacts with water and oxygen from the environment to form hydrated iron oxide (rust)
71
how is rusting a redox reaction?
iron is being oxidised (losing electrons). oxygen is being reduced (gaining electrons). both are taking place in the same reaction, so it's a redox reaction
72
what conditions are required for the rusting of iron?
water and oxygen
73
how could you carry out an experiment on the conditions required for rusting?
- 3 test tubes
1. iron nail in distilled water, test tube is open to the air WATER AND AIR
2. iron nail is also in distilled water, but the water is being boiled, removing any dissolved air. the water is covered in oil, preventing any air in the test tube from dissolving in the water WATER BUT NO OXYGEN
3. anhydrous calcium chloride powder, removing water from the air in the test tube. place a rubber bung on the test tube, preventing any moist air from entering OXYGEN BUT NO WATER
- leave these for several days, and look for changes
- 1's should be covered in rust. 2's and 3's nails should have no rust, as corrosion requires both air and water
74
is all of a metal corroded during corrosion?
only the surface metal is corroded, as it's the only part that's exposed to substances in the environment (e.g. water, oxygen)
- when iron rusts, however, the rust that forms at the surface gradually flakes off, revealing new metal underneath. this metal can now rust, and this will flake away. if left long enough, the entire chunk of iron can break down until there's nothing left
- in contrast, when aluminium corrodes, only the surface atoms are affected. when the surface atoms are oxidised, forming aluminium oxide, they form a protective layer around the aluminium
75
describe some barrier methods of protection:
barrier methods prevent oxygen and water from touching the iron
1. paint it. works well for really big pieces
2. oil/grease it. necessary if the object has moving parts, like a bike chain
3. electroplating
76
describe electroplating:
aluminium is commonly used. the surface naturally reacts with oxygen in the air to form a thin layer aluminium oxide, protecting the metal underneath from any further corrosion
- this could be referred to as a natural layer of oxide coating
- "uses electrolysis to cover the iron in a thin layer of another metal"
77
what is sacrificial protection?
- adding a more reactive metal to the iron, e.g. aluminium. if the object is exposed to oxygen, the more reactive metal will be oxidised instead of the iron, so the iron
won't rust
78
what does ductile mean?
it can be thread through wires
79
what is galvanising?
- coating a metal with zinc
- e.g. iron nails covered with zinc are galvanised nails
- e.g. coating railings with zinc. it's not structurally integral and can't be used by itself as it's too flexible.
- if the zinc is scratched, it still prevents corrosion as it's more reactive than the metal beneath, meaning it corrodes instead of the metal BOTH BARRIER AND SACRIFICIAL METHOD
80
what is an alloy, and how is it made?
contains a metal blended with other elements. it's a mixture
- melt the metal, mix in other elements, and allow the alloy to cool
81
what are the properties of a metal vs an alloy?
metal: malleable, ductile, good conductor of heat and electricity, high melting and boiling points
alloy: much stronger (no longer malleable)
82
name a use of alloys:
useful for purposes where they might be put under stress, e.g. in buildings
83
why are alloys harder than pure metals?
- in pure metals, the atoms form layers. hammering the metal means the atoms slide over each other, making them relatively soft
- the atoms in an alloy are different sizes, therefore disrupting the layers and stopping them from sliding, so they're harder
84
describe bronze:
- an alloy of copper and tin
- as it's extremely hard and tends not to corrode, it's used for statues
85
describe brass:
- alloy of copper and zinc
- although it's harder than pure copper, it can be formed into different shapes
- it's used for musical instruments and door handles
86
describe gold as an alloy:
- used in jewellery, but pure gold is too soft
- usually gold is alloyed with silver, copper, and zinc to make it harder
it's purity is rated in carats. 24 carats is 100% gold, whereas 18 carats is 75% gold
87
describe steel:
- alloys of iron containing non-specific amounts of the non-metal carbon
- also contains other metals
- high carbon steel is extremely hard and brittle. it tends to break if hit with a hammer. used to make cutting tools, such as chisels
- low carbon steel is softer and more easily shaped. it is used to make car bodies
88
what is a problem with steel?
- an alloy of iron, meaning it can rust. carbon can also corrode easily, and must be protected from the water and air
- to prevent that, as well as iron and carbon, stainless steel contains chromium and nickel
- stainless steel is hard, and resistant to corrosion. nickel is corrosion resistant and chromium makes it shiny
89
describe aluminium alloys:
- low density
- extremely useful, e.g. in plane fuselages
90
what is the difference between the strength, brittleness and hardness of a material?
- strength: the ability of a material to resist an applied force (it's hard to change the shape of a strong material)
- brittleness: how easily a material breaks when a force is applied (brittle materials snap easily)
- hardness: how well a material can resist being scratched or indented (hard materials don't scratch)
91
what are ceramics?
a group of hard, brittle, heat-resistant and corrosion-resistant materials
- made by shaping and then firing a non-metallic material (e.g. clay) at a high temperature
- two main groups include clay ceramics and glass
92
describe soda-lime glass:
TYPE OF CERAMIC
- most of the glass that we use
- ideal for items such as windows and bottles
- to make it, mix together sand (silicon oxide), sodium carbonate and limestone. heat this in a furnace until it melts. when it cools, it solidifies into any shape we want
- has a relatively low melting point, limiting its uses
93
describe borosilicate glass:
TYPE OF CERAMIC
- higher melting point than soda-lime glass
- useful for objects that require heating, e.g. kitchenware and labware
- made by melting a mixture of sand (silicon oxide) and boron trioxide
94
what are the benefits of glass?
transparent, strong, and a good thermal insulator, making it useful for windows, for example
95
describe clay ceramics:
TYPE OF CERAMIC
- unlike glass, clay is a mineral found in the ground
- when it's wet and soft, clay can be shaped, and is then heated to a high temperature in a furnace to harden
- includes brick, china, porcelain
- high compressive strength, which is why bricks are used for building
96
what is a ceramic, and how is it formed?
a material made out of clay soil, that has been dug out of the ground and heated in a kiln oven
- dig the clay out of the ground. shape it. bake it in a kiln oven
97
what are composites?
consists of two or more materials with different properties, that have been combined to produce a material with more desirable properties. made from two components:
- the reinforcement (consisting of long fibres/fragments of one material)
- this reinforcement is then bound together (surrounded) by a matrix or binder material. this is usually something that starts soft and then hardens
98
describe a Macintosh jacket composite:
has a thin layer of cotton between two layers of rubber. therefore, it's waterproof and warm
99
describe the carbon fibre composite:
the reinforcement material is fibres of carbon, and the matrix is a plastic resin
- very strong and very light, making it extremely useful in cars/aircraft parts
100
describe reinforced concrete (composite):
- has steel bars surrounded by concrete
- extremely strong, used to build buildings
101
what do the properties of polymers depend on?
the monomers it's made from and the conditions of the chemical reaction
- they're generally flexible, easily shaped and good insulators of heat and electricity
102
what two forms does poly(ethene) come in?
high density poly(ethene) - HDPE
low density poly(ethene) - LDPE
103
describe high density polymers:
- high density polymers have more polymer strands per unit space. they're more dense, and harder.
- conditions: low temperature/pressure, catalyst
- properties: more rigid, stronger
- uses: drainpipes
104
describe low density polymers:
- low density polymers have branches which separate the strands, meaning they're further away from each other. they're less dense, and less hard
- conditions: moderate temperatures, high pressures, catalyst
- properties: more flexible, weaker
- uses: carrier bags
105
how could we change the properties of a polymer through its formation conditions?
- temperature
- reaction pressure
- catalyst
106
describe thermosoftening polymers:
- made up of polymer chains joined by weak intermolecular forces
- heating the polymer causes the intermolecular forces to easily break, and now the polymer strands separate from each other and the polymer melts
- it can then be remolded into a different shape and will harden again when cooled
107
describe thermosetting polymers, and their structure:
- don't melt when we heat them
- lots of polymer chains are connected to each other by strong covalent bonds. these require lots of energy to break, so don't soften when heated. they're hard, strong, rigid
- instead, they burn at a higher temperature
- plug cases are thermosetting polymers
108
what is a use of ammonia, and how is it produced?
- makes nitrogen based fertilisers for farming, allowing us to grow all of our food
- the Haber process, which produces ammonia, however, is a reversible reaction, and so some ammonia breaks back down into nitrogen and hydrogen
109
what is the word equation for the Haber process?
nitrogen + hydrogen = ammonia (+heat)
- produces heat, so is exothermic
- reversible reaction
110
what is the production process of ammonia?
1. nitrogen and hydrogen are mixed together NO REACTION
2. they're then compressed, increasing the pressure to 200 atmospheres NO REACTION
3. placed into a chamber at 450 degrees celsius with a powder iron catalyst, and this is when they'll react together
4. this produces ammonia. cool and condense it, as ammonia has a low boiling point
5. any nitrogen/hydrogen in gas form that hasn't reacted is recycled back into the reactant mixture
111
where can nitrogen and hydrogen be sourced from?
- nitrogen is extracted from the air
- hydrogen can be produced by reacting methane (a hydrocarbon) with steam
112
why is the catalyst powdered in the Haber process?
increases its surface area, making it more effective
113
what is Le Chatelier's principle, and how does this help with the Haber process?
states that if a system is at equilibrium, and a change is made to any of the conditions, the system responds to counteract the change
- we can therefore adjust the temperature and the pressure to shift the position of equilibrium towards the right hand side, producing more ammonia
114
describe how we can change the temperature to produce more ammonia in the Haber process?
- the forward reaction is exothermic
- a relatively cool temperature will shift the position of equilibrium to the right hand side to favour the forward reaction and achieve a higher % yield
- however, a cool temperature will make the reaction slow (the particles need a lot of kinetic energy to react), so we must compromise between the rate of reaction and the position of equilibrium
- 450 degrees celsius is the compromise temperature, as we get a relatively fast rate and a relatively high yield of ammonia. the iron catalyst also increases the rate of reaction
- generating heat is also expensive, so a higher temperature would be too costly
115
describe how we can change the pressure to produce more ammonia in the Haber process?
- a high pressure will push the position of equilibrium to the right hand side, as it has less molecules
- high pressures also create a high rate of reaction, as they mean the particles collide with each other more frequently
- however, it's very dangerous and expensive to work with very high pressure, so we settle on a compromise pressure of 200 atmospheres
116
does a catalyst have any effect on the position of equilibrium?
no
117
what is a fertiliser?
- applied to the soil, in order to supply plants with nutrients
- replace the elements which have been taken up by plants
118
how did we used to make fertilisers, and how do we make them now?
- fertilisers used to be made from animal waste, e.g. cow manure
- now, we tend to use formulated fertilisers, made in factories. this involves combining certain chemicals in a specific ratio
119
describe NPK fertilisers:
- contain compounds of nitrogen, phosphorus, and potassium
- these elements improve agricultural productivity, helping plants to grow larger and more rapidly
- produced in large industrial facilities, where a variety of different raw materials are processed together to create the exact fertiliser required
- they're formulations of different salts, which contain the required elements in the percentages needed by the plants
120
why is nitrogen important to plants?
required to make amino acids and hence proteins, which are essential for growth
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how are compounds of nitrogen in NPK fertilisers produced?
- main compound is ammonium nitrate
- use ammonia, produced by the Haber process, and use it to create nitric acid
- react the nitric acid with more ammonia to make ammonium nitrate
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how are the compounds of potassium in NPK fertilisers produced?
- comes from the salts potassium chloride or potassium sulfate
- both of these are mined from the ground, and can be used directly without any further processing
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how are the compounds of phosphorus in NPK fertilisers produced?
- phosphate rock is mined from the ground
- however, the phosphate salts in the rock are insoluble, so plants can't use them as nutrients, so they can't be directly used in fertilisers: it must first be chemical processed
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how do we treat phosphate rock with nitric acid?
- treating it with nitric acid forms phosphoric acid and calcium nitrate
- phosphoric acid contains phosphorus, but this can't be directly added to plants - it must be neutralised with ammonia
- this produces ammonium phosphate, which can be used in the NPK fertiliser
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how can we treat phosphate rock with sulfuric acid?
- makes a mixture of calcium phosphate and calcium sulfate
- this mixture is called single superphosphate, which can be used in NPK fertilisers
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how can we treat phosphate rock with phosphoric acid?
- makes triple/calcium superphosphate
- this can be used in NPK fertilisers
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compare the production of ammonium nitrate (reacting ammonia with nitric acid) in a school lab vs in the industry:
- neutralisation reaction
SCHOOL LAB:
- dilute solutions of ammonia and nitric acid, making them safe to work with
- produce crystals using a water bath and a bunsen burner, requiring a lot of heat energy
- can only produce a small amount of ammonium nitrate in one go, a batch process
INDUSTRY:
- the ammonia is used as a gas, and the nitric acid is concentrated
- this is much more dangerous as the reaction is exothermic, so the heat produced must be safely removed. the heat is then used in later stages
- some of the heat energy for evaporation is provided by the earlier exothermic reaction
- the chemical is produced continuously, so thousands of kg can be produced easily
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describe natural fertilisers:
- e.g. seaweed
- uncertainty, as we're unsure of its exact NPK composition
