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topic 10- using resources (reuse and recycling (chemistry is improving…
topic 10- using resources
ceramics, composites and polymers
ceramics come in many different forms
clay
soft material when dug from ground
can be molded into different shapes
when its fired at high temps it hardens to form clay ceramic
ideal for pottery and bricks as is easy to mold
glass
generally transparent
can be molded when hot and can be brittle and thin
soda lime glass = mixture of limestone, sand and sodium carbonate; made by heating until it melts
borosilicate glass= has higher melting point than soda lime, mixture of sand and boron trioxide
composites are usually made from 2 different materials
composites are made from one material embedded in another
fibres/ fragments of a material (reinforcement) are surrounded by a matrix acting as a binder
e.g.
fiberglass= consists of glass fibres in polymer matrix - low density but strong used for skis and boats
carbon fibre= reinforcement made from carbon nanotubes or bonded carbon atoms in polymer matrix- light, strong; aerospace
concrete= aggregate (sand and gravel) embedded in cement- very strong; building material
polymers can have different properties
things that influence polymer properties: how its made, what is made from
e.g. low density polyethene made from ethane at moderate temp, high pressure, with catalyst- flexible (plastic bags)
high density polyethene made from ethane at low temp, low pressure, different catalyst- more rigid (drain pipes)
thermosoftening polymers= contain individual polymer chains entwined together with weak forces between chains - these plastics can be melted and remolded
thermosetting polymers= contains monomers that can form cross links between polymer chains, holding chains together in solid structure. don't soften when heated like thermosoftening- strong, hard rigid
properties of materials
different materials are suited to different jobs
ceramics= insulators of heat and electricity, brittle and stiff
composites= depend on the matrix and reinforcement, have many different uses
polymers are insulators of heat and electricity, flexible and are easily molded
metals= malleable, good conductors of heat and electricity, ductile, shiny and stiff
pure metals don't always have right properties
alloys are made by adding another element to the metal, disrupting the structure and making them harder
the regular structure of metals makes them soft
e.g. steel is an alloy of carbon and iron
bronze= copper + tin
brass= copper + zinc
gold alloys= gold + zinc, copper, silver (24 caret is 100% gold)
alluminium alloys make it stronger
corrosion
iron and steel corrode more than other metals
iron corrodes easily (rusts)
iron + oxygen + water ---> hydrated iron (III) oxide
to rust iron needs water and oxygen
corrosion only happens on surface where it is exposed to air
iron oxide flakes off leaving another surface of iron underneath to corrode
aluminum corrodes to form aluminum oxide layer which protects against further reaction
air and water are needed for rusting
if you put an iron nail in either water or oxygen it wont rust, it needs both
ways to prevent rusting
barriers
painting/ coating in plastic
electroplating- uses electrolysis to reduce metal ions onto iron electrode, can be used to coat iron in other metal which wont rust
oiling/ greasing
sacrificial method- involves placing more reactive ion (magnesium, zinc) with the iron so oxygen and water react with sacrificial ion instead of the iron
galvanization- spraying iron with zinc coat creating protective layer, if scratched zinc becomes a sacrificial ion
finite and renewable resources
natural resources come from earth, sea and air
form without human input
e.g. cotton, oil
some of these natural products can be replaced by synthetic products or improved by man made processes. e,g, rubber
agriculture provides conditions where natural resources can be enhanced for our needs
some natural resources will run out
renewable resources reform at a similar rate or faster than we use them e.g. timber
finite resources are not formed quickly enough to be replaceable
e.g. fossil fuels, nuclear fuels (uranium), metals
after their extracted, many finite resources undergo manmade processes to provide fuels and materials e,g, fractional distillation makes petrol
extracting finite resources has risks
many modern materials are made from raw, finite materials e.g. plastics
people have to balance social, economical and environmental effects of extracting finite resources
e.g. mining
reuse and recycling
chemistry is improving sustainability
sustainable development takes account needs of present society while not damaging lives of future generations
extracting processes are unsustainable due to amount of energy used and product wasted, processing resources into useful materials is also unsustainable as it uses energy from finite resources
to reduce use of finite resources people should use less
chemists can adapt proceses that use lower amounts of finite resources and are less damaging to environment e.g. catalysts
copper rich ores are short in supply
one way to improve sustainability is to extract copper from low grade ores (ores without much copper in)
bioleaching- bacteria are used to convert copper into soluble copper compounds, separating it from ore. leachate contains copper ions which can be extracted by electrolysis or displacement
phytomining- this involves growing plants that contain copper. the plants don't use copper so it builds up in leaves. plants are harvested and dried then burnt in furnace and the ash contains soluble copper compounds which can be extracted by electrolysis or displacement
traditional methods of copper mining damage environment
recycling metals
mining and extracting metals requires energy that comes from fossil fuels
recycling metals uses less energy, conserves finite resources and cuts down on landfill waste
metals are recycled by melting and casting into new shape
glass can be recycled
reduces amount of energy needed to make new glass and reduces waste in landfill
glass bottles can be reused without reshaping
glass is recycled and separate by colour and chemical composition
the glass is crushed and melted to be reshaped for new glass products
life cycle assessments
show total environmental costs
looks at every stage of products life and assesses impact on environment
getting raw materials
extracting raw materials damges local environment and creates pollution due to amount of energy needed
raw materials often need to be processed to extract desired materials which requires large amount of energy e.g. fractional distillation
manufacture and packaging
manufacturing and packaging requires a lot of energy resources and can create pollution e.g. carbon monoxide fumes
also waste products and how they are disposed of. some waste products of chemical reactions can be turned into useful chemicals, reducing pollution
using the product
the use of product can damage environment e.g. burning fossil fuels creates greenhouse gases
how long a product is used for or how many uses -products which need a lot of energy to make but last a long time waste less in long run
product disposal
products are often disposed in landfill sites which takes up space and pollutes land and water
energy is used to transport waste to landfill which produces pollutants
products might be incinerated which causes air pollution
problems with LCA's
the use of energy, natural resources and certain types of waste produced can be quantified but the effects of pollutants is harder to give a numerical value to
can be biased- take into opinions of person carrying out assessment
selective LCA's can be biased as they can be written to deliberately support claims of company to give positive advertising
potable water
potable water is drinkable
potable water is water that has been treated or is naturally safe for humans to drink
it is not pure- can contain dissolved substances e.g. flourine
the levels of dissolved substances mustn't be too high, pH must be between 6.5-8.5 so there are no microbes
the way it is produced depends on location
countries with rain, surface water, ground water
when it rains water can be collected as surface water (lakes) or ground water (in aquifers)
rainwater is fresh water, doesn't have much dissolved in it
warmer areas use ground water, cooler areas use surface water (surface water evaporates)
fresh water sources are treated through:
filtration- a wire mesh filters out twigs etc and then gravel and sand bed filter out any other solids
sterilization- the water is sterilized to kill microbes, can be done by adding chlorine, using ozone or ultraviolet light
countries with no rain or sw or gw but sea water
sea water is treated by desalination
distillation can be used
sea water is treated through:
distillation:
1)test pH, if pH too high or low neutralize it using titration but use pH meter
2) test water for prescense of sodium chloride by doing flame test if sodium ion present flame turns yellow. to test for chlorine add nitric acid and silver nitrate if chlorine present white precip forms
3) pour water into apparatus and heat flask from below. the water will boil and form steam leaving undissolved salts in flask. the steam will condense back to liquid in condenser
4) then retest water for sodium chloride to make sure it has been removed
reverse osmosis- salty water is passed through membrane that only allows water molecules to pass through large ions are trapped and seperated
both require LOTS OF ENERGY so they are expensive and no practical for producing lots of water
waste water treatment
comes from lots of different sources
when water is flushed down drain it goes to sewers and towards sewage treatment plants
agricultural systems produce waste water including nutrient run off and slurry from animal farms
sewage has to be treated to remove organic matter and harmful microbes before it can be put back into fresh water sources like rivers
industrial processes e.g. haber process produces waste water that has to be collected and treated
sewage treatment stages
1) sewage is screened (removing large material e.g. twigs, grit)
2) then its allowed to stand in a settlement tank where it undergoes sedimentation - heavier solids sink to bottom while lighter effluent floats to top
3) the effluent is removed and treated by biological aerobic digestion- air pumped through water so bacteria break down organic matter
4) the sludge from bottom is removed and transferred to large tanks where it is broken down by bacteria in anaerobic digestion
5) anaerobic digestion breaks down organic matter in sludge releasing methane gas - methane gas used for energy and remaining digested waste is used for fertilizer
6) for waste containing toxic substances additional stages of treatment may include adding chemicals, uv radiation or membrane
haber process
nitrogen and hydrogen are needed to make ammonia
nitrogen + hydrogen <--> ammonia +( heat)
N2 + 3H2 <--> 2NH3
nitrogen easily obtained from air (78%)
hydrogen made by reacting methane gas with steam to create hydrogen and carbon dioxide
conditions: passed over hot iron catalyst, 200atm pressure, 450 degrees
reaction is reversible so eventually reaches dynamic equilibrium
ammonia forms as gas but is liquefied when past through condensor
ammonia used to make ammoniam nitrate fertilizer
compromises made
forward reaction if exothermic - increasing temp will shift equilibriunm wrong way more reactant produced
ammonia yield greater at lower temps
low temps means slow rate of reaction
450 degrees is compromise between max yield and speed of reaction
high pressures shifts equilibrium towards products which maximizes the percentage yield and increases speed of reaction
however high pressure is expensive and dangerous to maintain
iron catalyst does not effect yield
NPK fertilizers
provide plants with elements needed for growth
formulated fertilizers are better than manure as they are more widely available, don't smell and have enough nutrients for crop growth
essential elements: nitrogen, phosphorus, potassium
fertilizers replace/ add more of the essential elements to increase crop yield and increase speed
NPK fertilizers are formulations containing elements in right %
ammonia is used to produce nitrogen containing compounds
ammonia can be reacted with oxygen and water to make nitric acid
ammonia reacts with acids to create ammonium salts
ammonia nitrate is good compound for fertilizer because nitrogen comes from 2 different places
NH3 + HNO3 ---> NH4NO3
ammonia + nitric acid ---> ammonium nitrate
lab method: uses filtration and crystallization. reactants are at lower concentration so less heat is produced (safer). after titration mixture needs to be crystalized to give ammonium nitrate crystals
industry method: carried out in giant vats at high concentrations resulting in a very exothermic reaction. the heat released evaporates the water to make a very concentrated ammonium nitrate product
phosphate and potassium are sourced from mined compounds
potassium chloride and sulfate can be mined
phosphate rocks are mined but phosphate salts are insoluble so cant be used by plant
reacting phosphate rock with nitric acid produces phosphoric acid and calcium nitrate
reacting phosphate rock with sulfuric acid to produce calcium sulfate and calcium phosphate