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Using Earth’s Resources
Human use of Earth’s resources – provide warmth, shelter, food & transport Natural resources, supplemented by agriculture – provide food, timber, clothing & fuels Finite resources, ocean, atmosphere – provide energy & materials Role of Chemistry Improve agricultural & industrial processes – provide new products & sustainable development To meet needs of current generations without compromising ability of future generations to meet their own needs Potable Water Type Description Dissolved substances Microbes Pure water Only contains water molecules No No Potable water Safe to drink (pH of 6.55 – 8.5) Low Extremely low Fresh water Collected in ground, lakes, rivers Low Low Ground water Fresh water found in underground streams & aquifers Low Yes Sea water In seas High Yes Waste water Used water from homes, industry & agriculture High Yes Hard water Contains Mg²⁺ and Ca²⁺ Low Yes What is in water filters that removes hardness from water? (1) Ion exchange resin State health benefits of drinking hard water (1) Hard water contains mineral content that maintains bones/teeth & reduces heart disease Describe how water in the United Kingdom is treated. Explain how this makes it safe to drink. What are the two main steps used to treat water from reservoirs? Give one reason for each step. (4) Choosing an appropriate source of fresh water In UK – rain coz low levels of dissolved substances, collects in the ground, lakes & rivers First pass the water through a wire mesh then filter to remove solids Sterilisation - add chlorine / ozone / UV light to kill microbes
Why do some water companies add fluoride to drinking water? (1) Improve dental health Explain why it's more difficult to produce drinking water from waste water than from water in lakes (3) Water needs more processes coz it contains more organic matters & microbes How could the water be tested to show it's pure? (2) Determine its boiling point, which should be 100°C Desalination If fresh water is limited → desalination of sea water By distillation By processes that use membranes eg reverse osmosis Both techniques require lots of energy hence quite expensive – impractical to produce large amount of water Name the substance removed from seawater by desalination (1) Sodium chloride Why is desalination expensive? (1) Requires a large amount of energy Suggest why water filters used in home contain particles of silver (1) Prevent growth of microbes Desalination of seawater can be carried out by processes that use membranes such as reverse osmosis. Describe one other way to desalinate sea water in a school laboratory. (4) Distillation Heat a flask (containing sea water) until it boils Use of a condenser / delivery tube Collect (pure water) in a boiling tube / beaker / flask Which two processes are avoided when manufacturing cans from recycled aluminium? Separating the aluminium using electrolysis Mining the aluminium ore from the ground
Alternative Methods of
Extracting Metals
**Methods of extracting copper from low-grade ores
- Phyto mining** Use plants to absorb metal compounds Harvest plants, then burn them to produce ash that contain metal compounds
- Bioleaching Use bacteria to produce leachate solutions that contain metal compounds Suggest two methods to obtain copper from solutions of copper compounds? (2) By displacement using scarp iron By electrolysis Why are Phyto mining and bioleaching used to extract copper? (1) Avoid digging, moving & disposing large amounts of rock Copper can be extracted by smelting copper-rich ores in a furnace. The equation for one of the reactions in the process is: Cu 2 S(s) + O 2 (g) 2 Cu(s) + SO 2 (g) Explain why the gaseous product should not be released into the atmosphere (2) Sulfur dioxide is an environmental pollutant causing acid rain Describe how copper compounds are obtained by Phyto mining (2) Grow plants on land containing copper ores, then burn the plants Ash (from burning) contains copper compounds Aluminium is extracted from an ore, called bauxite, by electrolysis of molten aluminium oxide. Aluminium is also widely recycled and the metal is obtained from the recycling process. Use your knowledge and understanding to compare these methods of producing aluminium. (6) Your answer should include The energy requirement Availability of resources Purity of the products Extraction from bauxite High temperature needed to melt bauxite/ore Large amount of electricity used
Higher energy costs Uses more natural resources Bauxite must be quarried so more damage to the environment Purity of aluminium produced is higher Recycling Reduces waste going to landfill Uses less natural resources Lower energy costs Aluminium must be separated from other materials Purity of aluminium is lower.
Packaging requirements similar (so neither has an advantage) Usage Both single-use however plastic bags can be reused Disposal Paper releases more energy if incinerated (so more energy can be used for other purposes) Paper are biodegradable so will decompose (so will not remain in landfill) – non toxic Poly(styrene) could release toxins on incineration Poly(styrene) will not decompose (so will remain in landfill) Poly(styrene) can be used to manufacture other products (so conserves energy or finite resources) Both can cause litter or visual pollution, get into the wild and harm animals Glass milk bottle Plastic milk bottle Raw materials Sand, limestone, salt Crude oil Bottle material Soda-lime glass HD poly(ethene) Initial stage in production of bottle material Limestone and salt used to produce sodium carbonate Production of naphtha fraction Maximum temperature in production process
1600 °C 850 °C
Number of times bottle can be used for milk
Size(s) of bottle 0.5 dm³ 0.5 dm³, 1 dm³, 2 dm³, 3 dm³ Percentage (%) of recycled material used in new bottles
Evaluate the production and use of bottles made from soda-lime glass and those made from HD poly(ethene). Use the information given and your knowledge and understanding to justify your choice of material for milk bottles. (6) Glass – 2 stages in production of soda-lime glass Glass – second stage, heating sand, limestone and sodium carbonate HDPE – 3 stages in production HDPE – second stage, cracking of naphtha to obtain ethene HDPE – third stage, polymerisation of ethene Fewer stages in glass production, may be quicker Higher temperature in glass manufacture, therefore maybe higher energy requirement Glass bottle can be reused Consideration of collection / cleaning costs to reuse glass bottles Other glass products can be made from recycled glass Plastic has greater range of sizes Both produced from limited raw materials Higher percentage recycled materials in glass conserves raw materials Limitation of LCAs: Making products involves many steps – impossible to quantify all of them Difficult to assess of the steps even if all are quantified
As assessment is very complex; can be manipulated to support a company for + advertising
Ways of reducing The Use of
Resources
↓ use, reuse & recycling by end users ↓ use of limited resources, energy sources, waste & environmental impacts Obtaining raw materials from the Earth by quarrying & mining causes environmental impacts Give two reasons why quarry (and mining) is bad for the environment (2) Visual, noise, dust pollution Habitat destruction Some products can be reused Glass bottles can be crushed & melted to make different glass products Other products cannot be reused → so recycled for different use Metals can be recycled by melting & recasting / reforming into different products Why should we recycle? (2) Save / conserve resources & energy Limited landfill space Less CO2 emission & quarrying / mining Suggest how local council could encourage recycling? (1) Provide recycling bins Provide education of need to recycle How is energy saved by recycling more plastics? (1) Less energy used Amount of separation required for recycling depends on material & properties required of the final product Scrap steel can be added to iron from blast furnace to reduce amount of iron needed to be extracted from iron ore
Using Materials
Common properties a material has: Melting point - the temperature at which a solid melts into a liquid. Conductivity - how well a material conducts electricity. Strength - the ability of a material to resist an applied force (it is hard to change the shape of a strong material). Hardness - how well a material can resist being scratched or indented (hard materials don't scratch). Brittleness - how easily a material breaks when a force it applied (brittle materials snap easily. Stiffness - how well a material can resist bending (a stiff material won't bend very much). Corrosion Destruction of materials by chemical reactions with substances in the environment Eg rusting 4Fe + 3O 2 + 6H 2 O (hydrated) → 4Fe(OH) 3 (iron oxide) – redox reaction How to prevent corrosion? Surface coating / barrier Sacrificial protection Apply a coating – acts as barrier Eg greasing (‘oil’ if the parts move like bike chain), painting or electroplating (using electrolysis to cover the iron in a thin layer of another metal) Aluminium has an oxide coating → protects metal from further corrosion Coatings are reactive Contain a more reactive metal so more reactive metal corrodes instead Zinc is used to galvanise iron ‘ galvanising’ forms a protective coating & if iron is exposed by scratch the more reactive zinc reacts with O 2 instead The corrosion of iron is called rusting. For rusting to take place both oxygen & water It’s only the surface metal that corrodes – exposed to substances in the environment In iron rusting, the rust formed in the surface gradually flakes off, revealing new metal underneath which rusts again, hence the cycle repeats However, when metal like aluminium corrodes, only the surface atoms are effected This is because when aluminium’s top layer is oxidizes, it forms a protective layer around it, preventing further rusting. Explain what would happen to the nails in each of the test tubes. (5) Tube 1: (nail) rusts because air / oxygen and water present Tube 2: (nail) does not rust because no water / only air / oxygen Tube 3: (nail) does not rust because no air / oxygen / only water
Tube 4: (nail) does not rust because paint is a barrier (to water / air / oxygen) or a protective layer / coating (against water / air / oxygen) Tube 5: (nail) does not rust because stainless steel resistant to corrosion Magnesium is fixed to some steel ships. Explain how this prevents the steel from rusting. (2) Mg is more reactive than Fe So, Mg provides sacrificial protection Explain why aluminium window frames do not corrode after they are made. (2) (Aluminium has a coating of) aluminium oxide (So, the aluminium oxide) protects the metal (from further corrosion)
Ceramics, polymers and
composites
Ceramics are hard to define, but are basically a group of hard , brittle , heat-resistant , and corrosion- resistant materials. They are made by shaping and then firing a non-metallic material, such as clay, at a high temperature. Two main groups of ceramics are clay ceramics and glass. Glass Hard, see-through(transparent), unreactive, good thermal insulator (useful for windows) Types Soda-lime glass Borosilicate glass How to make Heat a mixture of sand, NaCO 3 , limestone – cool molten liquid Melt sand & B 2 O 3 at higher temp than soda-lime glass Clay ceramic Eg pottery brick, China and porcelain. Made by shaping wet clay, then heating in a furnace - high compressive strength Polymers Polymers are large molecules of high relative molecular mass. Long chain of molecule made from joining many short molecules (monomers) together Strong intermolecular force - hard to break - solid at room temp Different polymers, different properties, different uses Poly(ethene) is not biodegradable. Give one problem caused by waste poly(ethene). (1) Disposal / lack of space / does not decompose in landfill sites Complete the equation below to show the formation of poly(propene) (3)
Properties of polymers Depends on what monomers they are made from & conditions under which they are made Generally, polymers are flexible , easily shaped , and good insulators of heat and electricity. Eg Low density (LD) & high density (HD) poly(ethene) are produced from ethene LDPE - low-density poly(ethene) HDPE - high-density poly(ethene) Conditions : Moderate temperatures, high pressure, catalyst Properties : More flexible but weaker Uses : Carrier bags Conditions : Low temperature/pressure, catalyst Properties : More rigid but stronger Uses : Drainpipes Thermosoftening polymer Thermosetting polymer Contain long polymer chains, held by weak intermolecular forces Chains are not joined together (but are tangled up with each other) Low melting point - soften and then melt when heated It can then be remoulded into a different shape and will harden again when cooled. Contain long polymer chains Chains are joined by covalent bonds Require lots of energy to break High melting point - do not soften or melt when heated These polymers are hard , strong and rigid. Melamine is a polymer used to make non-disposable cups. Melamine does not melt when it is heated. Explain why. (2) (Melamine is a) thermosetting polymer Which contains crosslinks / bonds between polymer chains Explain why thermosetting polymers are better than thermosoftening polymers for saucepan handles. (2) Thermosetting polymers do not melt (when heated) Due to cross-links (between chains)
The Haber process and the use of NPK
fertilisers
Used to manufacture ammonia to produce nitrogen-based fertilisers – allows growth for food needed Equation Nitrogen + hydrogen ⇌ ammonia N2 (g) + 3H2 (g) ⇌ 2NH3 (g) Produces heat – exothermic & reversible reaction Purified gases passed over… (conditions) Iron catalyst – to speed up the reaction High temp - 450°C (compromises between yield and rate) High pressure - 200atm (increases yield) Explain why a temperature of 450°C is used in the Haber process. 450°C is a compromise between percentage yield, rate of reaction, and cost. The forward reaction is exothermic, and so the reaction should be done at a low temperature to get a high yield. The reaction will be faster at higher temperatures because the particles will have more energy, and so will be more likely to collide with enough energy to react. Generating high temperatures is expensive, so we can't use a very high temperature. Explain why a pressure of 200 atmospheres is used in the Haber process. 200 atm is a compromise between percentage yield, rate of reaction, and cost. There are fewer molecules of product than reactant, so a higher pressure will result in a larger yield The reaction will be faster at higher pressures because the particles will have more energy and so will be more likely to collide and react. Generating high pressures is expensive, so we can't use a very high pressure. Separation of Ammonia: The reaction mixture contains ammonia , unreacted nitrogen , and hydrogen. The gases pass into a condenser : Ammonia has a higher boiling point and condenses into a liquid. Unreacted nitrogen and hydrogen remain gaseous and are recycled. Describe how the ammonia is separated from the other gases (2) Cooled Ammonia condenses / liquefies
What happens to the mixture of unreacted gases (nitrogen and hydrogen)? (1) Recycled back into the reaction The graph shows the percentage yield of ammonia using different conditions. Use the graph above to suggest the conditions that produce the greatest yield of ammonia. (1) 200 °C and 1000 atmospheric pressure Use the graph above to suggest and explain why the conditions used to produce ammonia in the Haber process are a temperature of 450 °C and a pressure of 200 atmospheres. (5) The reaction is reversible Forward reaction is exothermic so increased temperature lowers the yield of ammonia A lower temperature would decrease rate of reaction A higher pressure would increase the yield of ammonia coz the forward reaction produces the least number of (gaseous) molecules / moles Higher pressures would involve high cost / energy
ammonium salts. Phosphorate fertilizer Phosphate can be mined from the ground as phosphate rock. However, because the phosphate salts in the rock are insoluble, plants can’t use them as nutrients, and so they can't be used directly in fertilisers. Instead, we have to react the phosphate rocks with acids to produce soluble salts: Reaction with nitric acid produces phosphoric acid and calcium nitrate. Reaction with sulfuric acid produces calcium sulfate and calcium phosphate (this mixture is known as single superphosphate). Reaction with phosphoric acid only produces calcium phosphate (also called triple superphosphate). Potassium fertilizer Potassium fertiliser is the simplest to produce. Potassium chloride and potassium sulphate can be both be mined from the ground and then used directly in fertilisers.
In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Farmers use ammonium nitrate as a fertiliser for crops. Rainwater dissolves ammonium nitrate in the soil. Some of the dissolved ammonium nitrate runs off into rivers and lakes. Below shows three graphs A, B and C. The graphs show information about the use of ammonium nitrate as a fertiliser. A hectare is a measurement of an area of land. Suggest how much ammonium nitrate farmers should use per hectare. Give reasons for your answer. Use information from graphs A, B and C (6) Yield: Using fertiliser improves yield. Yield improved most up to about 200 kg (per ha) of fertiliser. Yield only increased slightly above about 200 kg (per ha). Profit: About 200 kg of fertiliser gives the most profit. Above about 200 kg (per ha) of fertiliser profit declines. Run off: Run off is at low levels until about 300 kg (per ha) of fertiliser. Above about 300 kg (per ha) of fertiliser, run off increases. Examples of linking of ideas: Overall, 200 kg gives high crop yield and most profit. In conclusion 200 kg gives high crop yield and low run off. 200 kg gives most profit and low run off. Examples of compromise: Profits go down after about 200 kg (per ha) of fertiliser because cost of fertiliser is not covered by increased yield. 200 kg gives the highest profit although it is not the highest yield.
