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Naming and representing the formulae of organic compounds
General formula is the simplest algebraic formula of a member of a homologous series
Structural formula is the minimal detail that shows the arrangement of atoms in a molecule
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Skeletal formula is the simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just a
carbon skeleton and associated functional groups
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Functional groups
Homologous series is a series of organic compounds with the same functional group but with each successive member
differing by CH₂
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An alkyl group has a formula of CnH2n+
Aliphatic is a compound containing carbon and hydrogen joined together in straight chains, branched chains or nonaromatic rings
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Aromatic is a compound containing a benzene ring
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Unsaturated has the presence of multiple carbon-carbon bonds and aromatic rings
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Reaction mechanisms
Homolytic fission is when each bonding atom receives one electron rom the bonded pair, forming two radicals
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A radical is a species with an unpaired electron
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This bond is explained using the
model of ‘orbital overlap’ that explains covalent bonding in organic compounds
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The orbital combines to form a
shared orbital that forms a bond between the atoms
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The bonded atoms are free to rotate around the σ-bond because the atomic orbitals between them will always
overlap
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5°, because the four bonding pairs repel
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They have two fewer hydrogens
than alkanes (assuming they have only one ring) so their general formula is
The advantage of adding cycloalkanes to alkanes in petrol are cycloalkanes will burn more efficiently so will promote
efficient combustion
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The longer the carbon chain, the higher the boiling point because there is more surface area of contact and more electrons
to interact so more induced dipole-dipole interactions
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The more branched the chain, the lower the boiling point because they have less surface area of contact so fewer induced
dipole-dipole interactions/van der Waals’
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Reactions of alkanes

Alkanes are unreactive because the C–C and C–H σ-bonds all have a large bond enthalpy, making them very strong and
therefore difficult to break
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If you burn (oxidise) alkanes with enough oxygen, you get carbon dioxide and water – this is a complete combustion
reaction
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Smaller alkanes turn
into gases more easily (more volatile), so they will burn more easily too
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Therefore, larger alkanes release more energy per mole than smaller alkanes, because
more CO₂ and H₂O are formed making them great fuels e
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propane is used as central heating and cooking fuel, butane is
bottled and sold as camping gas and petrol and diesel (made up of alkanes and additives) is used as transport fuels
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This is an
incomplete combustion reaction
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Some will produce particulate carbon or
small amounts of carbon dioxide
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The oxygen in
your bloodstream is carried around by haemoglobin and carbon monoxide is better at binding to haemoglobin than oxygen
is
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At very high concentrations, carbon monoxide can be fatal leading to death
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All
appliances that use an alkane-based fuel need to be properly ventilated and checked and monitored regularly
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When halogens such as chlorine and bromine react with alkanes in photochemical reactions, haloalkanes are formed
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During the formation of haloalkanes, a hydrogen atom is
substituted (replaced) by a halogen in a radical substitution reaction
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A mixture of methane
and chlorine will react when exposed to UV light to form chloromethane
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In the initiation step, radicals are produced
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The atoms are highly reactive radicals because
each one has an unpaired electron
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First the chlorine radical attacks a methane
molecule:
The new methyl radical can then attack another chlorine molecule:
The new chlorine radical can attack another methane molecule, and so on, until all the chlorine or methane molecules are
used up
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Many
radical chain reactions have heaps of possible termination reactions
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The limitations of radical substitution in synthesis are that a mixture of organic products is formed so you don’t always get
the product you’re after
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You would then have to separate the desired product from the other unwanted by-products
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This means there’s a greater chance of a
halogen radical to collide only with the alkane molecule and not with another haloalkane
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Therefore, a mixture of
isomers can be formed
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The σ-bond is
formed in the same way as it is in alkanes
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A π–bond
is a sideways overlap of adjacent p–orbitals above and below the bonding C atoms
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Double bonds don’t bend
much
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Even though atoms can’t rotate about the double
bond, things on the single bonds can still rotate
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A double bond (π–bond + σ-bond) is not twice as strong as a single bond (σ-bond)
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The three bonds
repel each other
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Stereoisomerism in alkenes
Stereoisomers are compounds with the same structural formula but a different arrangement of atoms in space
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In alkanes, the groups are free to rotate around the single C–C bonds, so
they don’t form E/Z isomers
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The
highest priority group on each of the C=C carbons is the one which has the atom with the highest atomic number directly
bonded to the carbon atom
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Cis-trans isomerism is a special case of E/Z isomerism in which two of the substituent groups attached to each carbon
atom of the C=C group are the same
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The trans-isomer is the one that has
the two identical groups on opposite sides of the C=C double bond
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The π–bond sticks out
above and below the rest of the molecule so is likely to be attacked by particles called electrophiles
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The low bond enthalpy of the π–bond also contributes to the reactivity of alkenes
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Alkenes react with hydrogen gas to produce alkanes
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g
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For
example:
Alkenes react with halogens to form dihaloalkanes
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The halogens add across the
double bond, and each of the carbon atoms ends up bonded to one halogen atom
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Use a pipette the add about 2cm³ of bromine water to a test tube
2
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Place a stopper over the test tube and shake the test tube
4
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Alkenes undergo electrophilic addition reaction with hydrogen halides to form haloalkanes
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g
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g
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Markownikoff’s rule is used to predict the formation of a major organic product in additional reactions of H–X to
unsymmetrical alkenes e
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H–Br to propene
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However, if the hydrogen halide adds to an unsymmetrical alkene, there are two possible products
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Three possible
carbocations are

Carbocations with more alkyl groups are more stable because the alkyl groups give electrons towards the positive charge
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More
products are formed via the more stable carbocation
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The individual small alkenes are
called monomers
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Addition polymerisation reactions can be written as:
n = a very large number of repeat units (monomers) in
the polymer
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Waste polymers and alternatives
All plastics are made up of polymers
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g
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g
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However, their unreactivity also means most
polymers aren’t biodegradable meaning they
won’t break down quickly
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The different methods of disposing of waste
plastic are shown on the left:
Some waste polymers are put into landfill sites, compacted and covered with soil
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This uses up a valuable resource and the growing number of waste generated means the
need to use landfill needs to be reduced as much as possible
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The heat released can be used to generate electricity
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HCl can be
removed from the gases produced during the combustion of PVC by passing them through scrubbers, which reacts it with
a base/carbonate, neutralising the gases
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Waste polymers can be sorted and recycled as many of them are made from non-renewable oil fractions
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g
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When cracking takes place, a
large number of products are formed because any carbon–carbon bond in the chain can break
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Biodegradable polymers naturally decompose in certain conditions – because organisms can digest them
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However they need certain conditions to decompose – lack of oxygen and moisture in landfill
sites so won’t decompose, biodegradable polymers still need to be separated from non-biodegradable polymers and
they’re more expensive than oil-based equivalents
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Most polymers are made from fossil fuels
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Properties of alcohols
Alcohols have the general formula
Alcohols are generally polar molecules due to the electronegative hydroxyl group, which pulls the electron in the C–OH
bond away from the carbon atom
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R is any alkyl group
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The partial charge on the hydrogen atom attracts the lone pair of oxygen from a neighbouring molecule, forming hydrogen
bonds
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In larger alcohols,
most of the molecule is a non-polar carbon chain, so there’s less attraction for the polar H₂O molecules meaning as
alcohols increase in size, their solubility in water decreases
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Alcohols form hydrogen bonds with each other
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g
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An alcohol can be primary, secondary or tertiary, depending on
which carbon atom the hydroxyl group –OH is bonded to
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Secondary
alcohols are given the notation 2° and the –OH group is attached
to a carbon with two alkyl groups attached
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Reactions of alcohols
The combustion of alcohols produces a pale blue flame
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g
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Primary alcohols are oxidised to aldehydes and can then be
oxidised to carboxylic acids
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You can control how far the alcohol is oxidised
by controlling the reaction conditions
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Their general formula is
Gently heat an excess of alcohol with a controlled amount of oxidising agent in a distillation apparatus, so the aldehyde
(boils at a lower temperature than the alcohol) is distilled off immediately
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The alcohol is mixed with an excess
oxidising agent and heated under reflux (you can
increase temperature to boil without losing volatile

solvents, reactants or products)
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Secondary alcohols are oxidised to ketones only
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In these reactions, the orange dichromate (VI) ion, K₂O₇²ˉ, is reduced to the green chromium (III) ion, Cr³⁺
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The resistance of tertiary alcohols can be used to distinguish tertiary alcohols from primary and secondary alcohols
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If the solution stays orange, it is a tertiary alcohol
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Alkenes can be formed by eliminating water from alcohols in an elimination
or dehydration reaction
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The mixture
is then heated to eliminate water
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There are often two possible alkene products
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Sometimes an alkene product can form E/Z isomers so a mixture of both isomers will form
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g
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The
hydroxyl (-OH) group is replaced by the halide so the alcohol becomes a
haloalkane
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Substitution reactions of haloalkanes
A haloalkane is an alkane with at least one halogen atom in place of a hydrogen atom
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Haloalkanes can be hydrolysed to
make alcohols
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g
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The general equation is
R represents an alkyl group
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A nucleophile is an electron pair donor
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Water is a weak nucleophile and is much slower at substituting the halogen
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The general
equation is
Adding silver nitrate means the silver ions will react with the halide ions as soon as they form, giving a silver halide
precipitate
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First, four flasks containing the same amount
of a different haloalkane, ethanol (as a solvent) and dilute silver nitrate solution
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A cross is under each flask and the time it takes for the
cross to disappear can be measured
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g
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Bromoalkanes aire a bit slower to react and
chloroalkanes are the slowest to form a precipitate
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The observations match their bond
enthalpies
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Weaker carbon-halogen bonds break
more easily so react faster
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Floroalknes have the strongest
bonds, so they’re the slowest at hydrolysing
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Environmental concerns from use of organohalogen compounds
Chlorofluorocarbons, CFCs, are haloalkanes containing only chlorine, fluorine and carbon – all the hydrogens are replaced
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They

were once used as propellants in aerosols, in fridges, dry cleaning and air-condition – until scientists realised CFCs
contribute to ozone depletion in the upper atmosphere
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It contains most of the atmosphere’s ozone
molecules, O₃, and acts as a chemical sunscreen by absorbing ultraviolet radiation that can cause sunburn and even skin
cancer
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It means the reaction needs to be imitated
by electromagnetic radiation
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It splits to form chlorine free radicals
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Cl● is the
catalyst
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Nitrogen oxides are produced by
car and aircraft engines, and thunderstorms
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The reactions showing how the ozone is broken down can be represented by
equations where R represents any radical
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International agreements have reduced the use of CFCs
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CFCs have a long lifetime in the atmosphere and it takes a long time for CFCs to reach upper
atmosphere
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HCFCs (hydrochlorofluorocarbons) and HFCs (hydrofluorocarbons) are used as temporary alternatives until safer products
are developed
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Hydrocarbons are also used in fridges but are greenhouse gases too
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Many industrial freezers and fridges
use ammonia as coolant gas, and carbon dioxide is used to make expanded polymers
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Practical skills on organic synthesis
Quick fit apparatus are time saving apparatus made of borosilicate glass that has low thermal expansion and high
resistance to thermal shock
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It works by gently heating a mixture in a distillation apparatus
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A thermometer is placed at the neck of the condenser and shows the
boiling point of the substance that is evaporating at any given time
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If the product of a reaction has a lower boiling point than the starting
materials, then the reaction mixture can be heated in a distillation
apparatus so that the product evaporates from the reaction mixture as it
forms
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Reflux
A reflux reaction can be used to react reactants when they are heated before
they catch fire or evaporate
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The chemicals used in organic reaction are often hazardous so a risk
assessment needs to be carried out before any reactions take place in the lab
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Redistillation can be used to separate
products and impurities if they have different boiling points
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The desired liquid is placed in a flask at the open end of the condenser when it has boiled and the flask is ready to collect
the product
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Separation
If a product is insoluble in water, then a separating funnel can be used to remove any impurities
that do dissolve in water, such as salts or water-soluble organic compounds e
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alcohols
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The funnel is shaken and allowed to settle
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Most of the water-soluble impurities are dissolved
in the aqueous layer
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The product may not be pure after separation – any organic impurities that don’t dissolve in water will still be in the organic
layer alongside the product
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Drying agents
Using separation can cause trace amounts of water to end up with the organic layer
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The salt is used as a drying agent – it binds to any
water present to become hydrated
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All the water has been removed once you are able to swirl the mixture and it looks like a snow globe (cloudy)
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The mixture can be filtered to remove the
solid drying agent
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The table gives a
summary of the homologous series
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It shows all the reactions with the intermediate
products, and the reagents needed for each reaction
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Chemists need to be able
to make one compound from another that can be useful for
things such as designing medicines
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In a synthetic route, any special procedures such as refluxing
need to be included and the conditions needed e
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high
temperature or pressure, or the presence of a catalyst
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If it says a reaction is carried out at 20°C, it just means it’s done
at room temperature
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In infrared spectroscopy, a beam of IR radiation is
passed through a sample of a chemical
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Bonds between different atoms in a molecule absorb
different frequencies of IR radiation
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Wavenumber is the measure used for the frequency
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Scientists have collected data to provide evidence for if and why
global warming and climate change are happening e
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analysing
air samples and seawater sample
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The correlation isn’t enough evidence to prove it is the cause of
global warming
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Some of the electromagnetic radiation from the Sun
reaches the Earth and is absorbed
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Various gases in the troposphere (lowest layer of the

atmosphere) absorbs some of the IR and re-emits it in all directions – including back to Earth, keeping the Earth warm
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The main greenhouse gases are water vapour, carbon dioxide and methane
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The greenhouse effect of gases in the atmosphere is dependent on the abundance in atmosphere, the ability to absorb
infrared radiation and the residence time
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It also leads to stormier, less predictable
weather
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In other regions, increased rainfall an flooding has brought diseases such as cholera
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The agreement ended in 2012 and currently has no replacement
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More renewable resources are used to reduce emissions, as there are less coal-burning factories for electricity
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Carbon capture and storage (CCS) minimises global warming as it reacts carbon dioxide with metal oxides
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An infrared spectrometer produces a graph, known as a spectrum
that shows you what frequencies of radiation the bonds in a
molecule are absorbing
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The peaks show you where radiation is
being absorbed – the peaks are upside down
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A breathalyser is a quick test to see if the alcohol intake is over the
limit
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Infrared spectroscopy can monitor the concentrations of polluting gases in the atmosphere including carbon monoxide and
nitrogen monoxide present in car emissions
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A mass spectrum is produced
by a mass spectrometer
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