C6 - global challenges Flashcards
which metals can be found in the earth as the metal itself rather than as a compound?
a few unreactive metals like gold
how do we get the rest of the metals?
by extracting them from rocks
what do ores contain?
enough metal to make extraction worthwhile
what is a metal ore?
a rock which contains enough metal to make it economically worthwhile extracting the metal from it
what is the ore in many cases?
an oxide of the metal
give an example of a metal ore
the main aluminium ore is called bauxite (it’s aluminium oxide)
how can metals be extracted from their ores?
- chemically
- using biological methods
what are the two ways to extract a metal from its ore chemically?
- by reduction using carbon
- by electrolysis
- displacement reactions
what might need to happen to an ore before the metal is extracted?
some ores may have to be concentrated before the metal is extracted, which involves getting rid of the unwanted rocky material
what can electrolysis be used to do?
purify the extracted metal
what happens when an ore is reduced?
oxygen is removed
what determines whether a metal can be extracted by reduction with carbon?
the position of the metal in the reactivity series
how are metals higher than carbon in the reactivity series extracted?
using electrolysis
how are metals lower than carbon in the reactivity series extracted?
by reduction using carbon
give an example of how a metal lower than carbon is extracted and explain why
iron oxide is reduced in a blast furnace to make iron; this is because carbon can only take the oxygen away from metals which are less reactive than carbon itself is
what are some metals higher than carbon in the reactivity series?
- potassium
- sodium
- calcium
- magnesium
- aluminium
what are some metals lower than carbon in the reactivity series?
- zinc
- iron
- tin
- copper
metals higher than carbon are extracted using electrolysis of what?
molten compounds
why do the compounds have to be molten for electrolysis?
so that the electrons and ions are free to move
during electrolysis, what happens?
- once the metal is melted, an electric current is passed through it
- the metal is discharged at the cathode and the non-metal at the anode
why is electrolysis so much more expensive than reduction with carbon?
electricity is expensive
give an example of a metal being extracted using electrolysis
- when alum is extracted from its ore (aluminium oxide) the ore is first dissolved in molten cryolite (an alluvium compound) so ions in ore are free to move
- during electrolysis, alluvium formed at cathode, where it sinks to bottom of cell and is siphoned off
- oxygen formed at the anode
how is copper purified?
by electrolysis
what is it called when copper is extracted by reduction with carbon and the ore is heated in a furnace?
smelting
when copper is extracted using reduction with carbon, why doesn’t it conduct electricity very well?
it’s impure
why do we need copper to be able to conduct electricity well?
a lot of copper is used to make electrical wiring
what is the supply of some metal rich ores like?
limited
what is happening to the demand for lots of metals and what is this causing?
demand is growing and this may lead to shortages in the future
what are scientists looking into new ways of extracting metals from?
- low-grade ores (ores that only contain small amounts of the metal)
- from waste that is currently produced when metals are extracted
what are some examples of new methods to extract metals?
- bioleaching
- phytomining
what are bioleaching and phytoextraction examples of?
biological methods to extract metals as they use living organisms
what happens during bioleaching?
- uses bacteria to separate metals from their ores
- bacteria gets energy from bonds between atoms in the ore, separating out metal from ore in process
- leachate (solution produced in process) contains metal ions which can be extracted by electrolysis or displacement with more reactive metal
what happens during phytomining?
- involves growing plants in soil containing metal compounds
- plants can’t use or get rid of metals so they gradually build up in leaves
- plants can be harvested, dried or burned in a furnace
- ash contains. metal compounds from which metal can be extracted by electrolysis or displacement reactions
what is a big advantage of biological. methods to extract metals (bioleaching and phytomining)?
traditional methods of mining are pretty damaging to the environment; these new methods have much smaller impact
what is a big disadvantage of bioleaching and phytomining?
they’re slow
what is an alloy?
a mixture of a metal and other elements
what can alloys be mixtures of?
- two or more different metals
- a metal and a non-metal
what are examples of alloys?
- steel
- brass
- bronze
- solder
- duralumin
why can alloys be more useful than the pure metal?
alloys often have properties that are different from the metals they’re made from
what is steel an alloy of?
iron and carbon
why can steel be more useful than iron?
- harder than iron
- stronger than iron (as long as amount of carbon doesn’t exceed about 1%)
- less likely to rust
what sort of things are made from steel?
- girders
- bridges
- engine parts
- cutlery
- washing machines
- saucepans
- ships
- drill bits
- cars
what is brass?
- alloy of copper and zinc
- most properties are mixture of this of copper and zinc
- brass harder than either of them
- used for making brass musical instruments e.g. trumpets
- used for fixtures and fittings e.g. screws
what is bronze?
- alloy of copper and tin
- harder and stronger than tin
- more resistant to corrosion than either
- used to make springs, motor bearings, bells and in sculpture
what is solder?
- usually alloy of lead and tin
- unlike pure materials, doesn’t have definite melting point but gradually solidifies as it cools
- useful for joining metal things together as easily worked e.g. to connect components in electrical circuits
- relatively low melting point so can be melted without deforming other components in circuit
what is duralumin?
- alloy of mostly aluminium (about 94%), small amounts of copper (around 4%), magnesium (about 1%) and often small amounts of manganese
- low density alloy
- stronger than aluminium
- strong and light so useful for making parts of aeroplanes/other aircraft
what is corrosion?
process where something is slowly damaged or destroyed by a chemical process
what is rusting a type of?
corrosion
what type of reaction is the rusting of iron?
redox reaction
what is needed in order for rusting to take place?
iron must be in contact with both oxygen and water
what is rust a form of?
hydrated iron(III) oxide
what is the equation for the formation of rust?
iron + oxygen + water = hydrated iron(III) oxide
what do other metals corrode to form when in the presence of oxygen and water?
their metal oxides
what can prevent corrosion?
oil, grease and paint (barriers)
what can painting be used for?
ideal for large and small structures (can also be nice/colourful)
when might oiling or greasing be used to prevent corrosion?
has to be used when moving parts e.g. bike chains
what will protect steel from corroding?
a coat of tin
what is tin plating?
where a coat of tin is applied to the object e.g. food cans
what does tin act as when it prevents corrosion?
a barrier (stopping water/oxygen in air from reaching surface of metal)
what must the tin stay in order to work to prevent corrosion?
must remain intact; if tin is scratched to reveal some of metal below, it will start to corrode
what can more reactive metals prevent metals from doing?
corroding
what is it called when more reactive metals are used to prevent corrosion?
the sacrificial method
how does the sacrificial method work?
you place a more reactive metal with whatever you don’t want to corrode; the water and oxygen then react with this ‘sacrficial’ metal instead of with the metal you’re protecting
what is galvanising?
- a coat of zinc is put onto an iron object to prevent rusting
- zinc acts as sacrificial protection as more reactive than iron so will lose electrons in preference to iron
- zinc acts as barrier
- steel buckets and corrugated iron roofing are often galvanised
besides galvanising, give another example of sacrificial protection
- blocks of metal e.g. magnesium can be bolted to less reactive metals to prevent corrosion
- magnesium loses electrons in preference to the less reactive metal
- used on ship hulls or underground pipes
what is the haber process?
an important industrial process which produces ammonia to make fertilisers
what is needed to make ammonia?
nitrogen and hydrogen
what is the equation for the haber process?
N2(g) + 3H2(g) <=> 2NH3(g) (+heat)
what happens to nitrogen and hydrogen before the haber process?
the gases are first purified
how is the nitrogen obtained for the haber process?
from the air, which is 78% nitrogen
how is the hydrogen obtained for the haber process?
from hydrocarbons from sources such as natural gas or crude oil
what does the haber process make?
- some of the nitrogen and hydrogen react to form ammonia
- because the reaction is reversible, ammonia breaks down again into nitrogen and hydrogen
what does the reversible reaction in the haber process reach?
an equilibrium
what is a word that describes the reaction conditions chosen for the haber process?
a compromise
in industry, what pressure and temperature is ammonia made at, and in the presence of what catalyst?
- ammonia made at pressure of 200atm
- temperature of 450 degrees celsius
- in the presence of an iron catalyst
which reaction do higher pressures favour in the haber process?
the forward reaction
(since there are 4 moles of gas on left for every 2 on right)
why is the pressure set as high as possible for the haber process?
to give the best yield without making the plant too expensive to build e.g. would be too expensive to build plant that would stand pressures of over 1000atm
in the haber process, is the forward reaction exothermic or endothermic?
exothermic
because the forward reaction is exothermic in the haber process, what would increasing the temperature do?
it would move the equilibrium position the wrong way so yield would be greater at lower temperatures
what does lowering the temperature do?
lowers rate of reaction
in industry, why is the temperature increased?
to get a faster rate of reaction
in the haber process, what is 450 degrees celsius a compromise between?
maximum yield and speed of reaction
how is the ammonia removed during the haber process?
the ammonia is formed as a gas but as it cools in the condenser it liquifies and is removed
what happens to the unused hydrogen and nitrogen in the haber process?
they’re are recycled so nothing is wasted
what does the iron catalyst do in the haber process?
- speeds up the reaction so gets it to equilibrium proportions more quickly
- reduces costs
- doesn’t affect position of equilibrium
why is the catalyst so important to the haber process?
without the catalyst the temperature would have to be increased even more to get a quick enough reaction, which would further decrease percentage yield
what do fertilisers do?
help plants grow
what are the three main essential elements in fertilisers?
- nitrogen
- phosphorus
- potassium
if plants don’t get enough nitrogen, phosphorus and potassium, what is affected?
their growth and life processes
would do fertilisers replace or provide more of in the soil and what does this help?
- replace missing elements or provide more of them
- helping to increase crop yield as crops grow faster and bigger
what can ammonia be neutralised with to produce fertilisers?
acids
what is ammonia?
a base
because ammonia is a base, what does it produce when neutralised by acids?
ammonium salts
what is ammonia really important for?
world food production as it’s a key ingredient of many fertilisers
if you neutralise ammonia with nitric acid what do you get and what is this good for?
ammonium nitrate
- especially good fertiliser as has high percentage of nitrogen
if you neutralise ammonia with sulfuric acid what do you get and what is this good for?
ammonium sulfate can also be used as a fertiliser
if you neutralise ammonia with phosphoric acid what do you get and what is this good for?
ammonium phosphate is a fertiliser
what is another fertiliser which involves nitric acid?
potassium nitrate which is made by neutralising nitric acid with potassium hydroxide
give an example of how a fertiliser factory may carry out several integrated processes to make fertilisers
- may make ammonia using haber process
- phosphorus from phosphate rock
- sulphuric acid using contact process
- nitric acid
these chemicals then used to make ammonium phosphates, ammonium sulfate and ammonium nitrate
how can fertilisers be made in a lab using a titration method?
- choose right acid (nitric, sulphuric or phosphoric) + alkali (ammonia or potassium hydroxide)
example = ammonium sulfate - set up apparatus, add few drops methyl orange indicator to ammonia (will turn yellow)
- slowly add sulfuric acid from burette to ammonia solution until turns to red; gently swirl flask as added, go slowly as reach end point; methyl orange = yellow in alkalis, red in acids, colour change means got ammonium sulfate solution
- ammonium sulfate solution not pure, still has methyl orange, so for pure ammonium sulfate crystals, note exactly how much sulphuric acid took to neutralise ammonia
- repeat titration using that volume of acid but no indicator
- for solid ammonium sulfate crystals gently evaporate solution using steam bath until small amount left
- leave to crystallise, filter out crystals and leave to dry
why can the titration method not be used to make fertilisers in industry?
- impractical to use burettes and steam baths for large quantities
- crystallisation is slow
what is the contact process used to make?
sulfuric acid
how does the contact process work?
stage 1 = making sulfur dioxide usually by burning sulfur in air
stage 2 = sulfur dioxide oxidised with help of a catalyst to make sulfur trioxide
stage 3 = sulfur trioxide used to make sulphuric acid
what is the equation for the first stage of the contact process (sulfur dioxide made)?
sulfur + oxygen = sulfur dioxide
S(s) + O2(g) = SO2(g)
what is the equation for the second stage of the contact process (sulfur trioxide made)?
sulfur dioxide + oxygen <=> sulfur trioxide
2SO2(g) + O2(g) <=> 2SO3(g)
what is the equation for the third stage of the contact process (sulfuric acid made)?
sulfur trioxide + water = sulfuric acid
SO3(g) + H2O(l) = H2SO4(aq)
in reality, why is the third stage a bit more complicated and what is done?
dissolving SO3 in water is dangerous as lots of heat produced so in practice you dissolve SO3 in sulfuric acid first
which reaction in the contact process is reversible?
stage 2
in industry, what are the conditions for the contact process a compromise between?
- rate of reaction
- yield
- cost
how is the temperature chosen for the contact process?
- oxidising sulfur dioxide to form sulfur trioxide is exothermic
- for higher yield, temperature should be reduced
- as lowering temp slows reaction compromise must be reached of 450 degrees celsius to get acceptable yield quickly
how is the pressure chosen for the contact process?
- 2 moles of gas on products side compared to 3 on reactants
- so for higher yield you’d expect pressure to be increased
- but high pressure is expensive and equilibrium already on right so unnecessary
- so reaction at/just above atmospheric pressure
how is the catalyst chosen for the contact process?
- increase rate of reaction, vanadium pentoxide catalyst used (V2O5)
- doesn’t change position of equilibrium
what temperature, pressure and catalyst are used for the contact process?
- 450 degrees Celsius
- at/just above atmospheric pressure
- vanadium pentoxide catalyst (V2O5)
what must industrial processes be?
economical
what should be considered when designing an industrial process?
- cost of raw materials
- availability of raw materials
- energy costs
- rate
- equilibrium position
how must the cost of raw materials be considered for industrial processes?
- starting materials may need to be refined or purified
- may need to make them with another chemical reaction
- cost of extracting/refining/making them
- if too expensive, manufacture of product may not be profitable
how must the availability of raw materials be considered for industrial processes?
- some raw materials e.g. crude oil non-renewable so will eventually run out
- try to use renewable or common raw materials
how must the energy costs be considered for industrial processes?
- costs associated with reaching/maintaining required conditions for reaction
- generally higher pressure/temp more expensive so lower used wherever possible
how must the rate be considered for industrial processes?
- needs to be reasonable rate
- may need to compromise yield
- graphs show rate changes with reaction conditions
- sometimes rate increases with one of reaction conditions or may be optimum conditions
how must the equilibrium position be considered for industrial processes?
- some industrial processes are reversible
- controlling position of equilibrium maximises amount of product made so helps make more profitable
- if equilibrium position lies to the left then low yield and if difficult/expensive to alter then reaction may not be viable
if a company wants to manufacture a new product, what will it carry out?
life cycle assessment
what do life cycle assessments show?
total environmental costs
what stages do life cycle assessments look at?
- materials and manufacture
- transport
- product use
- disposal
what is considered about the materials and manufacture for a life cycle assessment?
- metals must be mined/extracted from ores these require energy and cause pollution
- raw materials for chemical manufacture often come from crude oil (non-renewable/supplies decreasing)
- manufacturing requires lots of energy/other resources
- can cause pollution e.g. harmful gases (CO, HCl etc)
- waste products/disposal
- some waste may be recycled so reduces amount that ends up polluting environment
what is considered about transport for a life cycle assessment?
- transporting product to where it’s sold/used uses energy
- companies should consider most energy efficient transport
what is considered about the product use for a life cycle assessment?
using product may damage environment e.g.
- paint gives off toxic fumes
- burning fuels releases greenhouse gases and other harmful substances
- fertilisers can leach into streams/rivers and damage ecosystems
what is considered about disposal for a life cycle assessment?
- products often disposed of in a landfill site
- takes up space/pollutes land and water
- products may be incinerated which causes air pollution
what does extracting raw materials require?
energy
what does lots of the energy used to extract raw materials come from?
burning fossil fuels
what makes fossil fuels negative?
- running out so should be conserved
- contribute to acid rain/climate change
what are advantages of recycling materials?
- uses fraction of energy needed to extract/refine material from scratch
- energy not cheap so saves money
- finite amount of many raw materials so helps conserve
- recycling metal cuts amount of rubbish sent to landfill, which takes up space/pollutes surroundings
explain the reasons behind recycling aluminium
- if didn’t recycle, would need to mine more aluminium ore (4 tonnes for every 1 tonne aluminium needed)
- mining makes mess of landscape
- ore needs to be transported and aluminium extracted (lots of electricity)
- cost of sending used aluminium to landfill
- for every 1kg aluminium cans recycled you save: 95% or so energy needed to mine/extract ‘fresh’ aluminium, 4kg of aluminium ore and a lot of waste
what are some complications with recycling?
- not energy-free process as energy needed to reprocess materials into new forms
- items need sorting e.g. glass sometimes into diff colours
- need to compare energy usage for recycling vs new
- generally want option with lowest energy cost
- can only recycle material finite amount of times
- recycled material may be lower quality than original
what do properties of materials depend on?
the bonding in them
give some examples of different physical properties of different polymers
- strong, rigid polymers e.g. HDPE for water pipes
- light, stretchy polymers e.g. LDPE for plastic bags
- polystyrene foam in packaging to protect breakable things and thermal insulator
- heat-resistant polymers e.g. melamine resin and polypropylene for plastic kettles
what are ceramics?
- made by baking substances e.g. clay to produce brittle, stiff material e.g. glass, porcelain, bone china
what are pottery and bricks made from?
clay
what is clay?
a mineral formed from weathered/decomposed rock
what are advantages of clay?
- soft when dug from ground so easy to mould into different shapes for pottery and bricks
- can be hardened by firing at very high temperatures so ideal as building material e.g. clay bricks can withstand weight of lots more bricks on top
what is most glass made from?
by melting limestone, sand and soda
what are some key features of glass?
- generally transparent and strong
- can be moulded when hot and brittle when thin
what are composites made of?
one material (the reinforcement) embedded in another (the matrix/binder)
what do the properties of a composite depend on?
the properties of the materials it’s made from
what are some examples of composites?
- fibreglass
- concrete
- kevlar-based composites
- carbon fibre composites
describe fibreglass
- consists of fibres of glass embedded in matrix made of polymer
- low density (like polymer matrix)
- very strong (like glass)
- used for things like skis and boats
describe concrete
- made from aggregate (mixture of sand/gravel) embedded in cement
- high compressive strength
- ideal as building material e.g. skate parks
describe kevlar-based composites
- made from kevlar (very strong man-made polymer) embedded in another material
- kevlar often used as ingredient in composite materials as adds lots of strength with minimal weight
- used in cycling helmets, tennis racquets and ropes
describe carbon fibre composites
- made using carbon atoms bonded together to make carbon fibres or carbon nanotubes held together in polymer resin matrix
- expensive to make
- strong and light
- ideal for use in aerospace and sports car manufacturing
what are some properties of polymers and why does this make them useful?
- very adaptable e.g. often flexible so can be bent without breaking and moulded into many shapes
- often cheaper than most other materials
- tend to be less dense than ceramics so often used when designing products which need low mass
- thermal and electrical insulators
- can degrade and break down over time so polymer products don’t always last as long as those made from other materials
what are some properties of ceramics and why does this make them useful?
- insulators of heat and electricity
- more brittle/stiff than most materials
- strong and hard-wearing
- don’t degrade or corrode like other materials so last longer
what are some properties of metals and why does this make them useful?
- good conductors of heat and electricity
- malleable
- some corrode easily but products made from corrosion-resistant material can last for a long time
- usually less brittle than ceramiics/polymers so likely to deform but stay in one piece where other materials may shatter
what are some properties of composites and why does this make them useful?
- different properties depending on matrix/binder and reinforcement
- combination of component materials can be altered
- designed to have specific properties for specific purposes
- tend to be more expensive to produce than other materials
what are alkanes?
saturated hydrocarbons
what is a homologous series?
a group of chemicals that have similar chemical structures
what reactions can alkanes take part in?
combustion reactions
during a complete combustion reaction, what do alkanes burn in and what do they form?
they burn in oxygen to form carbon dioxide and water
what is the equation for a complete combustion reaction with ethane?
ethane + oxygen = carbon dioxide + water
C2H6 + 3.5O2 = 2CO2 +3H2O
what do incomplete combustion reactions happen in?
a limited supply of oxygen
during incomplete combustion, what is produced?
- carbon monoxide
- carbon in the form of soot can also be given out
what is the equation for an incomplete combustion reaction with ethane?
ethane + oxygen = carbon monoxide + water
C2H6 + 2.5O2 = 2CO +3H2O
what do alkenes have?
a c=c double bond
why are alkenes unsaturated?
they can make more bonds as the double bond can open up and allow the two carbon atoms to bond with other atoms
what can you use to test for an alkene?
bromine water
what will an alkene do when added to bromine water?
decolourise it (orange to colourless)
why will an alkene turn bromine water colourless?
the double bond can open up and form bonds with bromine
why don’t alkanes react with bromine water?
they don’t contain double bonds
what is the process of reacting alkenes with hydrogen called?
hydrogenation
what happens during hydrogenation?
the hydrogen reacts with the double-bonded carbons and adds across the double bond
what functional group do alcohols have?
-OH
what can be done to alcohols to form carboxylic acids?
they can be oxidised
what is an example of an oxidising agent?
potassium manganate (VII)
what is the oxidation of alcohols accompanied by with potassium magnate (VII)?
a colour change - the mixture turns from purple to colourless
what is the functional group of carboxylic acids?
-COOH
what are the two types of polymerisation?
- addition polymerisation
- condensation polymerisation
what are addition polymers made from?
unsaturated monomers
what type of bond do the monomers that make up addition polymers have?
a double covalent bond
what are unsaturated compounds?
molecules with at least one double covalent bond between carbon atoms
what are saturated compounds?
molecules with only a single bonds between carbon atoms
how does addition polymerisation work?
lots of unsaturated monomer molecules can open up their double bonds and join together to form polymer chains
what is needed to make addition polymers in a lab?
an initiator
after adding the initiator to the alkene monomers, what else may need to be done to the reaction mixture and what should be used to do it?
- may need to be heated
- because making addition polymers often involves flammable chemicals, should use a water bath rather than a bunsen burner to heat reaction vessel
how is polystyrene made?
heat phenylethene in a water bath with the initiator (in this case a chemical called di(dodecanoyl) peroxide)
what does condensation polymerisation usually involve?
two different types of monomer
how does condensation polymerisation work?
the monomer react together and bonds form between them, making polymer chains
what must each monomer contain for condensation polymerisation?
at least two functional groups (one on each end of the molecule)
what are polyesters and polyamides?
condensation polymers
how do polyesters form?
when carboxylic acid monomers and alcohol monomers react together
how do polyamides form?
made form carboxylic acid and amine monomers
what group does an amine contain?
-NH2
give an example of a condensation polymer than can be made in a lab?
Nylon-6,6
how is Nylon-6,6 made?
- mix 1,6-diaminohexane in water and one beaker
- in a separate beaker, mix 1,6-hexanedioyl in an organic solvent
- pour one solution on top of the other, if careful not to mix solutions, you get two distinct layers
- nylon is formed where these two layers meet
- you can extract this layer carefully by slowly lifting it out of the beaker with tweezers and collecting it by wrapping the nylon, which forms as a thread, around a rod
what are some naturally occurring polymers?
- DNA
- proteins
- carbohydrates
- starch and cellulose
describe DNA
- complex molecule containing genetic information
- contains two strands made of nucleotide monomers that bond together in a polymerisation reaction
- there are four different nucleotide monomers in DNA (A,G,C,T)
describe carbohydrates
- molecules containing carbon, oxygen and hydrogen
- used by living things to produce energy
describe starch and cellulose
- large complex carbohydrates
- made up of many smaller units of carbohydrates (known as sugars) joined together in a long chain
describe proteins
- amino acids form polymers known as proteins via condensation polymerisation
- proteins have many important uses in the human body e.g. in enzymes
are proteins polyesters or polyamides?
polyamides
what is crude oil separated into?
different hydrocarbon fractions
what is crude oil formed from?
the buried remains of plants and animals which, over millions of years and with high temperature and pressure, turned to crude oil (which can be drilled up)
what is crude oil a mixture of?
lots of different hydrocarbons
what is crude oil used as?
feedstock to create lots of petrochemicals
how are the different compounds in crude oil separated?
fractional distillation
how does fractional distillation work?
- oil is heated until most of it has turned to gas
- gases enter fractionating column (liquid, bitumen, drained off at bottom)
- in the column there’s a temperature gradient
- longer hydrocarbons = higher boiling points so turn back into liquids an drain out of column early on, near bottom
- shorter hydrocarbons turn to liquid/drain out much later near the top of the column (where it’s cooler)
- end up with separate fractions, each with a mix of hydrocarbons with similar boiling points
where is hottest/coolest in the fractionating column?
hottest = bottom
coolest = top
from bottom to top of the fractionating column, what is drained out?
- bitumen
- oil
- diesel
- kerosene (paraffin)
- naphtha
- petrol
- liquefied petroleum gas
what does fractional distillation rely on?
the fact that different hydrocarbons have different boiling points
why does crude oil separate?
because of different intermolecular forces
what are the two important types of bond in crude oil?
- strong covalent bonds between atoms within each hydrocarbon molecule
- intermolecular forces of attraction between different hydrocarbon molecules in the mixture
when the crude oil is heated up, what are the molecules supplied with and what does this cause?
- molecules supplied with extra energy
- makes them move about more
- eventually a molecule will have enough energy to overcome intermolecular forces that keep it with other molecules so is a gas
why don’t the covalent bonds in crude oil break?
they’re much stronger than the intermolecular forces
why do bigger hydrocarbons have higher boiling points than smaller hydrocarbons?
the intermolecular forces of attraction break more easily in small molecules because they’re not as strong as those between big molecules
what are a few examples of what crude oil provides energy for?
- generating electricity
- heating homes
what does oil provide for us?
- fuel for most modern transport
- raw materials needed to make various chemicals including plastics
as the earth’s population increases, why are more fossil fuels burned?
to provide electricity for:
- increased home use
- to run manufacturing industries
what are some alternative energy sources to oil?
- nuclear power
- wind power
why do some people think we should stop using oil for fuel?
to keep it for making plastics and other chemicals
what is the name of the process of splitting crude oil fractions from fractional distillation into smaller molecules?
cracking
what does cracking do?
turns long alkane molecules into smaller alkane and alkene molecules
what is cracking a form of?
thermal decomposition
what is thermal decomposition?
when one substance breaks down into at least two new ones when you heat it
why are a lot of longer molecules produced from fractional distillation cracked into smaller ones?
there’s more demand for products like petrol and diesel than for bitumen or lubricating oil
what does cracking produce which can be made to make polymers?
lots of alkene molecules
what are the two types of cracking?
- catalytic cracking
- steam cracking
how does catalytic cracking work?
- vaporised hydrocarbons passed over powdered catalyst at about 400-700 degrees celsius and 70atm
- aluminium oxide is catalyst used
- long-chain molecules split apart on surface of bits of catalyst
how doe steam cracking work?
a hydrocarbon is vaporised and mixed with steam at high temperature
what do fuel cells use to make electricity?
hydrogen and oxygen
what do hydrogen and oxygen give out when they react and why?
- hydrogen and oxygen react to produce water
- the reaction is exothermic so releases energy
- when new bonds formed, excess energy given out as heat
what is a fuel cell?
an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently
give an example of a fuel cell and how is it useful?
hydrogen-oxygen fuel cells combine hydrogen and oxygen to release heat energy and water = no pollutants
what do hydrogen-oxygen fuel cells involve?
a redox reaction
how does a hydrogen-oxygen fuel cell work?
- electrolyte often solution of phosphoric acid, electrodes often porous carbon with catalyst
- hydrogen goes into anode compartment and oxygen goes into cathode compartment
- at negative electrode hydrogen loses electrons to produce H+ ions (oxidation)
- at positive electrode, oxygen gains electrons from electrode and reacts with H+ ions from electrolyte to make water (reduction)
- electrons flow through external circuit from anode to cathode (electric current)
what is the equation at the anode of a fuel cell?
H2 = 2H+ + 2e-
what is the equation at the cathode of a fuel cell?
O2 + 4e- + 4H+ = 2H2O
what is the overall equation for a fuel cell?
hydrogen + oxygen = water
2H2 + O2 = 2H2O
what are some advantages of fuel cells?
- don’t generate pollutants
- efficient
what are some disadvantages of fuel cells?
- expensive to adapt current technology to run off fuel cells
- hydrogen is difficult and expensive to extract and store
what was the first phase of the evolution of the atmosphere?
- earth’s surface originally molten, no atmosphere
- eventually earth’s surface cooled and thin crust formed
- volcanoes kept erupting, releasing gases from inside earth; ‘degassing’ released CO2, steam, methane and ammonia
- after settling down, early atmosphere mostly CO2 and water vapour (little oxygen)
- water vapour later condensed to form oceans
what was the second phase of the evolution of the atmosphere?
- a lot of early CO2 dissolved into oceans
- nitrogen gas put into atmosphere; by ammonia reacting with oxygen and released by denitrifying bacteria
- nitrogen not very reactive so amount of N2 in atmosphere increased as being made not broken down
- green plants evolved; photosynthesis removed CO2 and produced O2
- O2 in air built up and much CO2 locked up in fossil fuels and sedimentary rocks
what was the third phase of the evolution of the atmosphere?
- build up of oxygen killed off early organisms that couldn’t tolerate it
- allowed evolution of more complex organisms which used oxygen
- oxygen created ozone layer (O3) which blocked harmful rays from sun and enabled even more complex organisms to evolve
- virtually no CO2 left now
what is the composition of the atmosphere like?
78% nitrogen
21% oxygen
0.93% argon
0.035% carbon dioxide
how does an increasing human population affect the composition of the air?
- more people = more respiration = more CO2
- more energy needed for lighting etc = burning fossil fuels = more CO2
- more land needed for building/food etc = deforestation = less photosynthesis removing CO2
what does the greenhouse effect help to do?
keep the earth warm
how does the greenhouse effect work?
- the sun gives out electromagnetic radiation
- some passes through the atmosphere
- electromagnetic radiation with short wavelengths absorbed by earth (warming it)
- earth radiates some of heat radiation it absorbs as longer wavelength infrared radiation
- some IR absorbed by greenhouse gases
- some IR re-emitted towards earth by greenhouse gases
- some IR re-emitted back into space
- absorption and re-emission of IR by greenhouse gases keeps earth warm
what are the greenhouse gases?
- gases in the atmosphere that can absorb and re-emit heat radiation
- only present in small amounts
- carbon dioxide, water vapour, methane
what happens if the concentration of greenhouse gases in the atmosphere increases?
you get an enhanced greenhouse gas effect
what happens with the enhanced greenhouse gas effect?
more heat radiation from the earth is absorbed and less is re-emitted back into space so the atmosphere heats up
what do increasing greenhouse gases cause?
climate change
what can global warming be described as?
anthropogenic
what is global warming a type of and what does it cause?
- type of climate change
- causes other types of climate change
e.g. changing rainfall patterns, could cause severe flooding due to polar ice caps melting
in order to prevent or slow down climate change, what do we need to do?
cut down the amount of greenhouse gases were releasing into the atmosphere
how can we reduce carbon dioxide emissions?
by limiting our use of fossil fuels e.g. walking/cycling rather than driving
what has the UK government done about energy efficiency?
- formed plans to encourage public/industry to become more energy efficient/use more renewable energy
- created financial incentives to reduce CO2 emissions
- increased research into new energy sources
what are two examples of alternative fuels being developed?
- ethanol
- biodiesel
what is ethanol?
- produced by plant material so known as biofuel
- made by fermentation
- used to power cars in some places
- often mixed with petrol to make better fuel
what are the pros of ethanol being an alternative fuel?
- CO2 released when it’s burnt was taken in by the plant as it grew so carbon neutral
- only other product is water
what are the cons of ethanol being an alternative fuel?
- engines need to be converted before they’ll work with ethanol fuels
- ethanol fuel not widely available
- worries that as demand increases, farmers may switch from food crops to crops to make ethanol which will increase food prices
what is biodiesel?
- another type of biofuel
- produced from vegetable oils e.g. rapeseed oil and soybean oil
- can be mixed with ordinary diesel fuel and used to run a diesel engine
what are the pros of biodiesel being an alternative fuel?
- carbon neutral
- engines don’t need to be converted
- produces less sulfur dioxide /pollutants than regular diesel/petrol
what are the cons of biodiesel being an alternative fuel?
- can’t make enough to completely replace diesel
- expensive to make
- could increase food prices like ethanol
what are some pollutants?
- CO2
- NO/NO2 (nitric oxides)
- particulates
- SO2 (sulphur dioxide)
- CO (carbon monoxide)
what is acid rain caused by?
sulfur dioxide and oxides of nitrogen
what does sulfur dioxide come from?
sulfur impurities in fossil fuels
where do nitrogen oxides come from?
created from reaction between nitrogen and oxygen in the air, caused by heat of burning e.g. can happen in internal combustion engines of cars
how is acid rain formed?
- when sulfur dioxide and oxides of nitrogen mix with clouds they form dilute sulfuric acid and dilute nitric acid
- this falls as acid rain
what are the main causes of acid rain?
power stations and internal combustion engines in cars
what affects can acid rain have?
- causes lakes to become acidic so many plants and animals die
- kills trees
- damages limestone buildings
- ruins some stone statues
- makes metals corrode
what can oxides of nitrogen cause besides acid rain?
photochemical smog
what is photochemical smog?
- a type of air pollution caused by sunlight acting on oxides of nitrogen
- these oxides combine with oxygen in air to produce ozone (O3)
what can ozone cause?
breathing difficulties, headaches and tiredness
what affect does carbon monoxide have?
- can stop blood doing job of carrying oxygen
- lack of oxygen can lead to fainting, coma or death
how is carbon monoxide formed?
when carbon compounds are burnt without enough oxygen (incomplete combustion)
give one way carbon monoxide is produced
incomplete combustion in petrol or diesel car engines
what is particulate carbon caused by?
incomplete combustion
what affect does particulate carbon have?
- if escape into atmosphere they float around
- eventually, they fall back to ground and deposit as soot
- reduce air quality and can worsen respiratory problems
what are some domestic uses of water?
- drinking
- washing things
in the UK, where do we get our water from?
- surface water
- ground water
- waste water
why is treating wastewater preferable to disposing of it?
disposing of it can be polluting
what does how easy wastewater is to treat depend on?
the levels of contaminants in it
where is water purified?
water treatment plants
what are the processes of purifying water?
- filtration
- sedimentation
- chlorination
what happens during filtration?
a wire mesh screens out large twigs etc and then gravel and sand beds filter out any other solid bits
what happens during sedimentation?
iron sulfate or aluminium sulfate added to water, making fine particles clump together and settle at the bottom
what happens during chlorination?
chlorine gas bubbled through to kill harmful bacteria and other microbes
what does tap water have to meet?
strict safety standards
what is water that is fit to drink called?
potable water
what are some sources of pollutants in tap water?
- nitrate residues from excess fertiliser ‘run-off’ into rivers and lakes
- lead compounds from old lead pipes
- pesticide residues from spraying pesticides too near rivers/lakes
why would too many nitrates in drinking water be bad?
- can cause serious health problems
- prevent blood from carrying oxygen properly
why would too much lead in drinking water be bad?
- very poisonous
how can sea water be made potable?
- distillation
- desalination
how does distillation of sea water work?
can ensure you collect solvent when separating mixture e.g. water from sea water
what is bad about distillation?
- uses lots of energy
- therefore very expensive
- not practical for producing large quantities of fresh water
how does desalination of sea water work?
- uses reverse osmosis with special filter to remove salts
what is bad about desalination?
- still uses lots of energy
describe a more detailed explanation of the water treatment process
- upon exiting river or reservoir, water passes through series of grated bars to remove large objects
- water then enters settlement tank (sand/soil settle out)
- sedimentation: aluminium sulfate and lime added to water; small particles of dirt clump together and sink to bottom forming sludge to go to landfill
- water passed through filter made of fine sand; removes any remaining particles of mud/grit so water is clear
- chlorination; water looks clean but could still have deadly microbes so sterilised with small amounts of chlorine
- pH of water check/corrected to ensure neutrality
- water stored in tanks until needed
- water pumped to homes, school, offices, factories etc
what are aluminium sulfate and lime examples of?
coagulants
