Topic 10 - Using Resources Flashcards
1
Q
What are natural resources?
A
Natural resources are all around us and provide us with the materials we need for shelter, food, warmth and transport.
2
Q
What can natural resources be? (2)
A
- Living: plants and animals
- Non-living: Minerals, fossil fuels, water and air
3
Q
What are finite resources?
A
Some resources can be replaced by synthetic products. Resources that can not be replaced are called finite.
4
Q
How does chemistry play an important role in the development of new materials?
A
Chemistry plays an important role in the development of new materials through sustainable processes that enable the need of the current generation to be met without compromising the availability of natural resources for future generations.
5
Q
What is rubber? What is it an example of?
A
Rubber, which is extracted from the sap of trees (called latex), is an example of a natural product that can be replaced by a synthetic one.
6
Q
What is the replacement material for rubber?
A
The replacement material for rubber are polymers which have been developed to specifically replace the rubber in many products.
7
Q
What is an example of how scientific advancement has allowed us to maximise the production of natural products?
A
The use of fertilisers to enhance crop yields.
8
Q
What two things can natural resources be classified as?
A
- Renewable
- Non-renewable (can be described as finite)
9
Q
What are renewable resources?
A
Renewable resources are those which will not run out in the foreseeable future as they can be replenished or replaced.
10
Q
What is an example of a renewable?
A
Timber is an example of a renewable resource as trees and forests can be replanted after the wood has been harvested, although they do take years to replenish.
11
Q
What are non-renewable resources?
A
Finite or non-renewable resources are those that don’t reform quickly enough or don’t reform at all.
12
Q
What are examples of non-renewable resources?
A
Examples include minerals from the Earth’s crust and metal ores.
13
Q
What happens after extraction what makes the extraction process less sustainable?
A
After extraction, many resources require further processing to make the desired products. These processes require energy and make the extraction process less sustainable.
14
Q
What are examples of processes that require energy following extraction, making them less sustainable?
A
Examples include the reduction of metals from ores and the fractional distillation of crude oil.
15
Q
Why does the extraction of non-renewable resources carries risks?
A
The Earth’s natural resources are being depleted and large amounts of energy are being consumed in the process of extraction.
16
Q
What is potable water?
A
Potable water is water that has been processed and is safe for human consumption and daily use.
17
Q
What is the difference between potable and pure water?
A
The difference between pure water and potable water is that pure water is solely made up of H2O molecules, whereas potable water may contain different substances, usually dissolved minerals and salts.
18
Q
What characteristics should potable water have? (3)
A
- Have a pH between 6.5 and 8.5.
- The dissolved substances (e.g. salts) will be present is very small regulated quantities
- Be free of bacteria or potentially harmful microbes
19
Q
When is water considered fresh water?
A
When it is relatively free from dissolved substances. An example of this is rainwater.
20
Q
What is surface water?
A
Water can collect in reservoirs, lakes and rivers and is known as surface water.
21
Q
What are aquifers? What kind of water do they store?
A
Porous rocks that store water underground. Water stored here is known as groundwater.
22
Q
What do methods used to produce potable water depend on?
A
The methods used to produce potable water depend on available supplies of water and local conditions.
23
Q
What are the three steps in producing potable water from groundwater?
A
- choosing an appropriate source of fresh water
- passing the water through filter beds
- sterilising
24
Q
How does filtration work in the process of producing potable water from groundwater? (2)
A
- Debris such as pieces of soil and dirt, small pebbles, twigs, etc. are removed by a wire mesh screen
- After this, other debris is filtered through sand beds and gravel
25
How does sterilisation work in the process of producing potable water from groundwater? (2)
* Ultraviolet light or ozone can be used to sterilise water or alternatively chlorine gas is bubbled through the water
* This removes any dangerous bacteria or microbes
26
When is desalination used?
Where aquifers are not present and/or the collection of surface water is limited/fresh water supplies are limited, the process of desalination must be used to provide potable water to the population.
27
What is desalination?
Desalination involves the treatment of seawater to remove the salt by distillation or reverse osmosis, a process that involves the use of membranes.
28
How does desalination work?
When salt water is put through a semi-permeable membrane, only water molecules can pass through it. This happens as the membrane stops larger molecules and ions passing through.
29
What are the cons of desalination?
Desalination is an expensive process as it consumes large amounts of energy and is not ideal when producing large quantities of fresh water.
30
Where is desalination used?
It is used in regions with a very hot climate such as Saudi Arabia.
31
What is the 5 step method for required practical 8 - analysing a sample of water?
1. Use universal indicator to test the pH of the water.
2. Measure and record the mass of an empty evaporating basin.
3. Pour 10 cm3
water into the evaporating basin and evaporate the water using a
bunsen burner until the most of the water has evaporated.
4. Once the evaporating basin is cool, reweigh and record the change in mass.
5. Calculate the mass of dissolved solids in the water.
32
What is the 4 step method for required practical 8 - purifying a sample of water by distillation?
1. Place the water sample in a conical flask and set up the apparatus for distillation.
2. Heat the water gently using a bunsen burner until it boils. Then reduce the heat so the
water boils gently.
3. Collect around 1 cm depth of water in the cooled test tube, then stop turn the bunsen
burner off.
4. Analyse the water you have distilled with cobalt chloride paper.
33
How do you set up the apparatus for distillation in required practical 8? (3)
* Conical flask with delivery tube with bung over bunsen burner
* 1 boiling tube with clamp stand in an ice bath
* Delivery tube goes to boiling tube
34
Why must domestic and agricultural sewage be processed? What can it become? (3)
* Both domestic and agricultural sewage needs to be processed to remove organic matter, harmful microbes, particulates and toxins.
* This can then be safely returned to freshwater sources i.e. lakes and rivers.
* If this process did not take place, it could potentially pose health risks for the population.
35
What happens to water produced by the Haber process and other industrial processes?
* Waste water that is produced by the Haber process and other industrial processes needs to be gathered and treated appropriately.
* Harmful chemicals and organic matter are present in industrial waste.
* This therefore means that additional treatment has to be in place to ensure it is safe for the environment.
36
What are the 4 steps of sewage treatment at a sewage treatment plant?
* Screening and grit removal
* Sedimentation
* Aerobic digestion
* Anaerobic digestion
37
How does screening and grit removal work?
This is the first stage of treatment and it removes large materials such as plastic bags and twigs and grit by screening.
38
How does sedimentation work? (2)
* Sedimentation is the second step and it occurs in a settlement tank.
* The water is allowed to stand still in the tank while heavier solids sink to the bottom creating sewage sludge, whilst lighter matter which is also known as effluent, floats to the top
39
How does aerobic digestion work - sewage treatment? (2)
* The effluent is removed and treated by biological aerobic digestion.
* This involves pumping air into the water to encourage the breakdown of organic matter and other microbes by aerobic bacteria.
40
How does anaerobic digestion work - sewage treatment? (4)
* Anaerobic digestion is then used to break down the sewage sludge from the bottom of the settlement tank.
* The sludge is firstly removed and placed in large tanks where bacteria break it down.
* Anaerobic digestion releases methane gas as a by product from the organic matter in the sludge.
* Methane gas is used as a source of energy and the leftover, digested waste as a fertiliser.
41
What happens when here is toxic substances in sewage water? (2)
* When there are toxic substances within waste water, it is important to use additional phases of treatment.
* This can include using membranes, adding additional chemicals e.g. to precipitate metals out of solution, and also U.V. radiation.
42
When/where is sewage water often treated?
Sewage water is often treated in areas where there is little freshwater available.
43
How does sewage treatment compare to desalination and preparing groundwater?
Though the process of sewage treatment is longer than processing and preparing freshwater, it uses less energy than the desalination of salt water.
44
When is extraction of metal ores viable?
Extraction of metal ores from the ground is only economically viable when the ore contains sufficiently high proportions of the useful metal, such as iron ores and aluminium ores.
45
How are low-grade ores being extracted? Example? (2)
* For low-grade ores (ores with lower quantities of metals) other techniques are being developed to meet global demand.
* This is happening in particular with nickel and copper as their ores are becoming more and more scarce.
46
What are phytoextraction and bioleaching examples of?
Phytoextraction and bioleaching (bacterial) are two relatively new methods of extracting metals that rely on biological processes, which avoid the significant environmental damage caused by the more traditional methods of mining.
47
Why are biological methods of extraction better than traditional mining?
Traditional mining involves a great deal of digging, moving and disposing of large amounts of rock, which biological methods avoid.
48
What is phytomining?
This process takes advantage of how some plants absorb metals through their roots.
49
How does phytomining work? (4)
* The plants are grown in areas known to contain metals of interest in the soil.
* As the plants grow the metals are taken up through the plants vascular system and become concentrated in specific parts such as their shoots and leaves.
* These parts of the plant are harvested, dried and burned.
* The resulting ash contains metal compounds from which the useful metals can be extracted by displacement reactions or electrolysis.
50
What is bioleaching?
Bioleaching is a technique that makes use of bacteria to extract metals from metal ores.
51
How does bioleaching work? (3)
* Some strains of bacteria are capable of breaking down ores to form acidic solutions containing metals ions such as copper(II).
* The solution is called a leachate which contains significant quantities of metal ions.
* The ions can then be reduced to the solid metal form and extracted by displacement reactions or electrolysis.
52
What are the negatives of bioleaching?
Although bioleaching does not require high temperatures, it does produce toxic substances which need to be treated so they don't contaminate the environment.
53
What is bioleaching used in? (2)
Bioleaching is not only used for the primary extraction of metals, but it is also used in mining waste clean up operations.
54
What are phytomining and bioleaching mostly used for?
Phytoextraction and bioleaching are principally used for copper extraction due to the high global demand for copper, but these methods can be applied to other metals..
55
What is a life cycle assessment?
A life cycle assessment (LCA) is an analysis of the overall environmental impact that a product may have throughout its lifetime.
56
What 4 main stages are the life cycles of products broken down into for an LCA?
* Raw Materials
* Manufacture
* Usage
* Disposal
57
What negative environmental impacts can obtaining raw materials include? (for an LCA) (2)
* Using up limited resources such as ores and crude oil
* Damaging habitats through deforestation or mining
58
What negative environmental impacts can manufacturing processes have? (for an LCA) (3)
* Using up land for factories
* The use of fossil fuelled machines for production and transport
* Production of waste
59
What impacts does use have in an LCA? (2)
* Usage of a product may also affect the environment although it depends on the type of product
* For example, a wooden desk has very little impact whereas a car will have a significant impact (air pollution)
60
What negative environmental impacts can disposal have? (for an LCA) (2)
* Using up space at landfill sites
* Whether the product or its parts can be recycled
61
How is an LCA carried out - objectively/ numerically etc.? (2)
* Use of water, resources, energy sources and production of some wastes can be fairly easily quantified.
* Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LCA is not a purely objective process.
62
Why should you be careful if you are provided with a life cycle assessment which is abbreviated when evaluating a product? (2)
* Be careful if you are provided with a life cycle assessment which is abbreviated when evaluating a product as they do not give the complete picture.
* They are often used in advertising campaigns to support claims to highlight the benefits to the environment of a product without explaining the negative environmental impact it may have.
63
LCA for plastic bags - raw materials
Crude oil is a finite source which requires a lot of energy to process
64
LCA for plastic bags - manufacturing (3)
* Fractional distillation, cracking & polymerisation require lots of energy
* Not much waste as crude oil is completely used
* Cheap to manufacture
65
LCA for plastic bags - usage
Is reusable
66
LCA for plastic bags - disposal (2)
* Can be recycled but is costly and produces pollution.
* Can be stored in landfill, takes up space and is not biodegradable
67
LCA for paper bags - raw materials (2)
* Recycled paper, or tress.
* Making paper requires more energy than recycling paper but much less than making plastics
68
LCA for paper bags - manufacturing
Pulping paper uses a lot of energy, sulfur dioxide and produces waste
69
LCA for paper bags - usage
Most are not reusable
70
LCA for plastic bags - disposal
Biodegradable, non-toxic and can be recycled
71
Conclusions for LCA of plastic vs paper bags (4)
* Considering both life-cycle assessments, the plastic bag may be the better option. Even though they aren’t biodegradable, they do have a much longer lifespan and thus are less harmful than paper bags.
* Much depends on the usage of the item:
-If the paper bag is recycled then it could be more favourable to use it.
-If the plastic bag is used only once, then then the argument for using plastic bags is less favourable.
72
What are everyday materials such as glass, metal, plastics, ceramics produced from? What can we do to them? (2)
* Everyday materials such as glass, metal, plastics, ceramics are produced from natural but finite sources.
* Some products made from these materials can be reused which saves energy and decreases the environmental impact.
73
Can glass be reused?
Glass bottles only need to be washed and sterilised before they can be reused.
74
What can some products that can be reused have done to them?
Other products cannot be reused in the way glass can, but can be processed and recycled.
75
How can metals be recycled?
Metals can be melted and recast into new shapes.
76
Why do recycled materials sometimes have to be kept separate? Example? (2)
* Sometimes the materials being recycled need to be kept separate, depending on what the use of the recycled material will be.
* Iron for example can be recycled together with waste steel as both materials can be added to a blast furnace, reducing the use of iron ore.
77
Why does glass have to be recycled sometimes? What happens to it then?
Glass that is broken or damaged and cannot be reused is separated by colour and composition before being recycled. The glass is then crushed and melted, and remoulded into shape for its new use.
78
What are the economic advantages of recycling? (2)
* It is economically beneficial to recycle metals, especially those that are costly to extract such as aluminium.
* Recycling is fast becoming a major industry and provides employment which feeds back into the economy.
79
What are the environmental advantages of recycling? (3)
* Mining and extracting metal from ores has detrimental effects on the environment and ecosystems.
* It is much more energy efficient to recycle metals than it is to extract them as melting and re-moulding requires less energy.
* Recycling decreases the amount of waste produced, hence saving space at landfill sites and energy in transport.
80
How is recycling advantageous in terms of raw materials? (3)
* There is a limited supply of every material on Earth.
* As global populations increase there is a greater need for effective recycling methods to attain sustainable development.
* Mining and extraction use up valuable fossil fuels, which contributes to climate change.
81
What are the disadvantages of recycling? (4)
* Collection and transport of material to be recycled requires energy and fuel.
* Workers, vehicles and work sites need to be organised and maintained.
* Materials need to be sorted before they can be recycled which also requires energy and labour.
* Products made from recycled materials may not always be of the same quality as the original.
82
What is corrosion?
Corrosion is the destruction of materials by chemical substances in their environment which act on them over a period of time.
83
How can most metals corrode?
Most metals can corrode in the presence of oxygen to form the corresponding metal oxide.
84
What is rusting?
Rusting is the name given specifically to the corrosion of iron in the presence of water and oxygen from the air.
85
What is the word equation for rusting?
iron + water + oxygen ⟶ hydrated iron(III)oxide
86
What is rust?
Rust is a soft solid substance that flakes off the surface of iron easily, exposing fresh iron below which then undergoes rusting.
87
What does the fact that rust flakes off exposing fresh iron that rusts mean for iron?
This means that over time all of the iron rusts and its structure becomes weakened.
88
What is the difference between corrosion and rusting?
Corrosion and rusting are not the same process. Corrosion is the general term used to describe the degradation of metal surfaces whereas rusting is the specific type of corrosion that happens to iron.
89
How can you investigate the conditions for rusting? (4)
* Set up 3 test tubes with nails in them.
* First one - fill with water until top third of nail only is out of water => air and water
* Second one - fill with boiling water and then pour oil in => just water
* Third one - add calcium chloride => just air
90
What are the results for the three nails in investigating rust? (half filled with water, boiling water and oil, calcium chloride)
* First one => rusts as it is in contact with both air (which contains oxygen) and water.
* Second one => does not rust as it is not in contact with air because the oil provides a barrier to prevent oxygen diffusing into the boiled water.
* Third one => does not rust as it is not in contact with water because calcium chloride absorbs any water molecules present due to moisture.
91
How can rust be prevented using barrier methods?
Rust can be prevented by coating iron with barriers that prevent the iron from coming into contact with water and oxygen.
92
What is the main negative of using barrier methods to prevent rust?
If the coatings are washed away or scratched, the iron is once again exposed to water and oxygen and will rust.
93
Why is the rusting of iron a big problem compared to the corrosion of some other metals?
Unlike some other metals, once iron begins to rust it will continue to corrode internally as rust is porous and allows both air and water to come into contact with fresh metal underneath any barrier surfaces that have been broken or scratched.
94
What are some examples of common barrier methods? (4)
* paint
* oil
* grease
* electroplating
95
How does sacrificial protection work to prevent rust?
* Iron can be prevented from rusting using the reactivity series.
* A more reactive metal can be attached to a less reactive metal.
* The more reactive metal will oxidise and therefore corrode first, protecting the less reactive metal from corrosion.
96
What is a common example of sacrificial protection to prevent rust?
Zinc bars on the side of steel ships
97
How do zinc bars on the side of steel ships work as a sacrificial protection method for rust?
* Zinc is more reactive than iron therefore will lose its electrons more easily than iron and is oxidised more easily.
* For continued protection, the zinc bars have to be replaced before they completely corrode.
98
What is galvanising?
Galvanising is a process where the iron is coated with a layer of zinc, to be protected. This can be done by electroplating or dipping it into molten zinc.
99
How does galvanising work?
* ZnCO(3) is formed when zinc reacts with oxygen and carbon dioxide in the air and protects the iron by the barrier method.
* If the coating is damaged or scratched, the iron is still protected from rusting by sacrificial protection.
100
How is aluminium protected from corrosion?
Aluminium has an oxide coating that protects the metal from further corrosion. The oxide layer acts as a barrier .
101
What is an alloy?
An alloy is a mixture of two or more metals or metal with a non-metal such as carbon.
102
What is steel made from?
Steels are alloys of iron that contain specific amounts of carbon and other metals.
103
How do the properties of alloys differ from pure metals? (2)
* They can be stronger and harder
* They are resistance to corrosion or extreme temperatures
104
Why are alloys harder than pure metals?
* Alloys contain atoms of different sizes.
* This distorts the regular arrangements of atoms.
* So it is more difficult for the layers of atoms to slide over each other.
105
What is bronze? How does it differ from copper? What is it used for? (3)
* Bronze is an alloy made of copper and tin.
* It is harder than copper.
* It is used to make ornaments and medals.
106
What is brass? What are its main properties? What is it used for? (3)
* Brass is an alloy which contains copper and zinc.
* It is decorative and corrosion resistant.
* It is used for low friction ornamental purposes such as plumbing and carpentry fittings.
107
What are gold alloys usually made with? What are they used for?
* Gold + silver, copper and zinc
* Used to make jewellery
108
What are carats?
Carats are used to express the purity of gold jewellery.
109
How do carats work? (3)
* Pure gold with nothing else added is said to be 24 carat.
* A 12 carat piece of gold jewellery therefore contains 50% gold.
* For example a 12 carat necklace that weighs 50g contains 50% gold, so 25 grams.
110
What is steel with a high carbon level like?
High carbon steel is strong but brittle
111
What is steel with a low carbon level like?
Low carbon steel is softer and more easily shaped
112
What is stainless steel? What is it like?
Stainless steels (steel containing chromium and nickel) are hard and resistant to corrosion
113
What are aluminium alloys made from? What are they used for? What are they like? (4)
* Aluminium is mixed with copper, manganese and silicon
* It is used for aircraft body production as aluminium alloys tend to be stronger and lighter than pure aluminium.
* It is also more corrosion resistant than aluminium.
* They are low density.
114
What are high carbon steels used for?
Cutting tools (very hard, but also brittle)
115
What are low carbon steels used for?
Building frames, cookware, car bodies (Softer and more easily shaped)
116
What are stainless steels used for?
Cookware, cutlery, car bodies
117
What is magnalium?
Alloy of Aluminium and magnesium
118
What is magnalium used for?
Aircraft construction and production of fireworks (more stable than pure magnesium but still burns brightly)
119
What are ceramics? What are they used for? (2)
* Ceramics are non-metal solids with high melting points.
* They have widely used in construction materials and domestic appliances.
120
Why is glass the ideal material for making windows? (2)
* Transparent and strong, glass insulates against heat and its transparency makes glass the ideal material for making windows.
* Glass ceramics are also more durable than other materials hence they are better suited for use in windows than plastic.
121
What are the 2 main types of glass?
* Soda-lime glass
* Borosilicate glass
122
How is soda-lime glass made?
Most of the glass produced is soda-lime glass which is made by heating a mixture of limestone, sand and sodium carbonate (soda) until it melts. On cooling, the mixture solidifies to form glass.
123
How is borosilicate glass formed? How does it compare to soda-lime glass? (2)
* This is made in the same way as soda-lime glass but is made using sand and boron trioxide.
* It has a higher melting point than soda-lime glass.
124
What is clay?
Clay is a soft material dug up from the earth.
125
How is clay a useful material? (2)
* When it is soft and wet it can be moulded into different shapes.
* When it is fired at high temperatures, it will harden to form a clay ceramic.
126
What can clay ceramics be used for? Why?
Clay ceramics are very strong so can be used as bricks which can withstand high pressures and weights.
127
What do the properties of a polymer depend on? (2)
* The monomers it is made from
* The conditions under which the polymer is made
128
What are the types of poly(ethene)?
Ethene can form high density (HD) poly(ethene) and low density (LD) poly(ethene).
129
How is low density poly(ethene) made? What is it used for? (2)
* Low density poly(ethene) is made at high pressure and moderate temperature.
* This is used for bags and bottles where flexibility is needed.
130
How is high density poly(ethene) made? What is it used for? (2)
* High density poly(ethene) is produced at lower temperatures and pressures and with the use of a catalyst.
* This polymer has a more rigid, solid structure and is used to produce water tanks, mouldings and drain pipes.
131
What can polymers be divided into?
thermosoftening and thermosetting polymers
132
What are thermosetting polymers?
Thermosetting polymers consist of polymer chains which have strong cross-links between them.
133
What are the characteristics of thermosetting polymers? Where are they used? (3)
* These polymers are strong and rigid structures that don’t melt when they are heated because lots of energy would be required to overcome the cross-links.
* They are commonly used in electrical plugs.
* They do not melt when heated.
134
What are thermosoftening polymers?
Thermosoftening polymers consist of individual, tangled polymer chains with no cross-links between them.
135
What are the characteristics of thermosoftening polymers? Where are they used? (3)
* These polymers have low melting points, can be melted and remoulded to form different shapes.
* They are commonly used to make packaging and plastic bottles.
* They melt when heated.
136
What is a composite?
Most composites are made of two materials, a matrix or binder surrounding and binding together fibres or fragments of the other material, which is called the reinforcement.
137
What is wood an example of? What is it made up of?
* Natural composite
* Matrix => organic polymer
* Reinforcement => cellulose fibres
138
How is fibre glass made up as a composite?
* Matrix => Polymer resin
* Reinforcement => Fibres of glass
139
What are the properties and uses of fibre glass?
* Properties => strong, lightweight and resistant to corrosion
* Uses => Boats, aircrafts and car bodies
140
How is carbon fibre made up as a composite?
* Matrix => Polymer resin
* Reinforcement => Carbon fibres OR Carbon nanotubes
141
What are the properties and uses of carbon fibre?
* Properties => Very strong, very lightweight, stiff
* Uses => aerospace, sports equipment, vehicles
142
How is concrete made up as a composite?
* Matrix => Cement
* Reinforcement => Rocks, sand and gravel
143
What are the properties and uses of concrete?
* Properties => Durable, strong and fire-resistant
* Uses => Building material, roads and bridges
144
How is wood and plastic made up as a composite?
* Matrix => Thermo-plastic
* Reinforcement => Fibres of wood
145
What are the properties and uses of a wood and plastic composite?
* Properties => Durable, water resistant, does not corrode
* Uses => Outdoor furniture, decking and fences
146
What is the Haber process? (2)
* Ammonia is manufactured using the Haber Process which occurs in five stages.
* The reactants are hydrogen and nitrogen which are extracted from methane and the air respectively.
147
What are the 5 stages of the Haber process?
* H(2) and N(2) gases are pumped into the compressor through pipes.
* The gases are compressed to about 200 atmospheres inside the compressor.
* The pressurised gases are pumped into a tank containing layers of catalytic iron beds at a temperature of 450°C. Some of the hydrogen and nitrogen react to form ammonia.
* Unreacted H(2) and N(2) and product ammonia pass into a cooling tank. The ammonia is liquefied and removed to pressurised storage vessels.
* The unreacted H(2) and N(2) gases are recycled back into the system.
148
What is the reversible reaction to form ammonia?
N(2) (g) + 3H(2) (g) ⇌ 2NH(3) (g)
149
How do we get the nitrogen for the Haber process?
The air contains 78% nitrogen and it is removed by fractional distillation.
150
How do we get the hyrogen for the Haber process?
Hydrogen is derived from methane (CH4) in a process called steam reforming.
151
What is affected by reaction conditions like temperature and pressure in reversible reactions?
If the reaction is reversible then the position of equilibrium is affected by changes in these conditions and often we must consider a trade-off between the rate of reaction and product yield.
152
At what conditions does the reversible reaction for ammonia produce the most yield?
* as the pressure increases, so does the yield at any given temperature
* as the temperature decreases, the yield increases
153
What are the economic considerations for the Haber process?
In the Haber Process the raw materials are readily available and inexpensive to purify.
154
How is the temperature of 450ºC decided for the Haber process? (4)
* A higher temperature would favour the backwards reaction as it is endothermic (takes in heat) so a higher yield of reactants would be made.
* If a lower temperature is used it favours the forward reaction as it is exothermic (releases heat) so a higher yield of products will be made.
* However at a lower temperature the rate of reaction is very slow.
* So 450ºC is a compromise temperature between having a lower yield of products but being made more quickly.
155
How is the pressure of 200 atm decided for the Haber process? (4)
* A lower pressure would favour the reverse reaction as the system will try to increase the pressure by creating more molecules (4 molecules of gaseous reactants) so a higher yield of reactants will be made.
* A higher pressure would favour the forward reaction as it will try to decrease the pressure by creating fewer molecules (2 molecules of gaseous products) so a higher yield of products will be made.
* However, high pressures can be dangerous and very expensive equipment is needed.
* So 200 atm is a compromise pressure between a lower yield of products being made safely and economically.
156
How does a catalyst impact a reversible reaction? Why?
* The presence of a catalyst does not affect the position of equilibrium but it does increase the rate at which equilibrium is reached.
* This is because the catalyst increases the rate of both the forward and backward reactions by the same amount (by providing an alternative pathway requiring lower activation energy).
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What does a catalyst allow for in terms of the Haber process?
* It allows for an acceptable yield to be achieved at a lower temperature by lowering the activation energy required.
* Without it the process would have to be carried out at an even higher temperature, increasing costs and decreasing yield as the higher temperature breaks down more of the NH(3) molecules.
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What are NPK fertilisers? How are they used?
* Compounds containing nitrogen, potassium and phosphorus are used as fertilisers to increase crop yields.
* NPK fertilisers are formulations of various salts containing appropriate percentages of all three elements.
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What do the three essential elements of NPK fertilisers do?
* Nitrogen promotes healthy leaves and to make proteins
* Potassium promotes growth, healthy fruit and flowers
* Phosphorus promotes healthy roots
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Why are artificial fertilisers so advantageous compared to natural fertilisers?
A distinct advantage of artificial fertilisers is that they can be designed for specific needs whereas in natural fertilisers, such seaweed or manure, the proportions of elements cannot be controlled.
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Why must fertilisers be water soluble?
Fertilisers must be water soluble so the nutrients they provide can be effectively absorbed and transported by the plant.
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What is ammonia?
Ammonia is an alkaline substance and neutralises acids producing a salt and water.
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What useful things can ammonia do?
* The salt it produces contains the ammonium ion, NH(4)+, which is a component of several fertilisers.
* Ammonia also undergoes oxidation to produce nitric acid, HNO(3).
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Why is nitric acid important?
Nitric acid is used as the source of the nitrate ion, NO(3)–, which is another important ion found in fertilisers.
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What is ammonium nitrate?
A fertiliser and one of the most important ammonium salts.
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What is the reaction for ammonium nitrate?
ammonia + nitric acid → ammonium nitrate
NH(3) (aq) + HNO(3) (aq) → NH(4)NO(3) (aq)
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How can ammonium nitrate be prepared?
It is prepared on large scale industrial proportions but can also be prepared in the laboratory using a different method. In the laboratory it is prepared by titrating ammonia with sulfuric acid.
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What is the equation for titrating ammonia with sulfuric acid?
2NH(3) (aq) + H(2)SO(4) (aq) → (NH(4))(2)SO(4) (aq)
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Lab production of ammonium sulfate - equipment
Simple equipment needed, prepared using titration apparatus
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Lab production of ammonium sulfate - reactant concentration
Low concentrations, less heat released
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Lab production of ammonium sulfate - separation of product
Crystallisation is used, slow process
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Industrial production of ammonium sulfate - equipment
Hugely expensive and complex
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Industrial production of ammonium sulfate - reactant concentration
High concentrations, very exothermic reaction
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Industrial production of ammonium sulfate - separation of product
The heat produced is used to evaporate water from the reaction mixture to make a very concentrated ammonium nitrate product
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What are phosphate rocks used for?
Phosphate rocks are mined and then treated to produce various water soluble compounds that can be used in fertilisers.
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Are phosphate rocks soluble? What does this mean?
The rock itself is insoluble in water so it is usually reacted with:
nitric acid
sulfuric acid
phosphoric acid
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What happens in the reaction with phosphate rocks and nitric acid? (2)
* Phosphoric acid and calcium nitrate are produced.
* The phosphoric acid is neutralised with ammonia forming ammonium phosphate.
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What happens in the reaction with phosphate rocks and sulfuric acid? (2)
* A mixture of calcium phosphate and calcium sulfate is produced.
* This mixture is known as single superphosphate.
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What happens in the reaction with phosphate rocks and phosphoric acid? (2)
* Calcium phosphate is produced.
* This is known as triple superphosphate.
