Download CFCs and Alcohols

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What are CFCs?
CFC stands for chlorofluorocarbon.
CFCs are a family of compounds that contain only chlorine,
fluorine and carbon atoms.
Here are some examples:
CCl2F2
Cl2FC-CClF2
Dichlorodifluoromethane
1,1,2-trichloro-1,2,2trifluoroethane
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Naming CFCs
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What are the properties of CFCs?
CFCs contain strong covalent bonds. This means that
they are very inert (unreactive).
CFCs therefore last for a long time in the environment as
they don’t decompose or react with other substances easily.
They are also insoluble in water, and have low melting and
boiling points.
boiling point: –30°C
melting point: –158°C
boiling point: 48°C
melting point: –35°C
What state are these CFCs at room temperature?
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What are CFCs used for?
During the 1930s, an American engineer named Thomas
Midgely discovered that CFCs were suitable for use as
coolants in refrigerators.
This was a very useful discovery
because the refrigerants used
previously were toxic compounds
like ammonia and sulfur dioxide.
In the 1960s, other uses for
CFCs started to be found:
as propellants for aerosol cans
and to inject bubbles into plastic
to make foams for insulation.
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What is the ozone layer
The ozone layer is a portion of the
stratosphere (upper atmosphere).
It contains the gas ozone (O3) which
absorbs ultraviolet (UV) radiation
emitted from the Sun.
There is strong evidence that UV
radiation is harmful. Scientists
believe that it causes skin cancer
and cataracts, and can also damage
plants and micro-organisms.
In the late 1970s and early 1980s,
scientists noticed that the ozone
layer was being depleted.
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How was the CFC problem discovered?
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How do CFCs react with ozone?
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How do CFCs react with ozone?
The chlorine free radical is actually a chlorine atom. It is
extremely reactive because it has seven outer electrons
– one short of a full shell.
Chlorine free radicals react with ozone:
Cl•
+
O3

ClO•
+
O2
The reaction produces another free radical species: ClO•.
This can also react with ozone:
ClO• +
O3

Cl•
+
2O2
This process forms a chain reaction: chlorine free
radicals are used up in the first step, but then re-produced
in the second step.
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CFCs and chain reactions
Chlorine free radicals are regenerated in the second step of
the chain reaction, therefore a single chlorine radical can
destroy 100,000 ozone molecules.
This image shows
the amount of
ozone over
Antarctica. Dark
blues and purples
indicate low
levels of ozone.
How has the
ozone layer
changed?
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Is ozone depletion slowing?
In the 1980s, scientists discovered that ozone was being
destroyed by the chlorofluorocarbons (CFCs) widely used in
aerosols and refrigerators. CFCs can stay in the environment
for 50 years, destroying ozone long after they are produced.
However, international regulations
to reduce CFC emissions may be
helping to repair the ozone layer.
Studies in 2006 showed that the
hole in the ozone layer is not
getting bigger. It is possible that if
CFCs remain banned, the ozone
layer could return to normal levels.
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What are the alternatives to CFCs?
Two families of compounds are now used in place of CFCs:
 hydrofluorocarbons (HFCs)
 alkanes.
These compounds do not contain chlorine atoms, so cannot
release chlorine free radicals into the atmosphere.
difluoromethane
methane
However, both these families of compounds are powerful
greenhouse gases.
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Voting activity: replacing CFCs
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CFC, alkane or HFC?
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CFCs: true or false
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What are alcohols?
Alcohols are a family of organic compounds that contain
carbon, hydrogen and oxygen atoms.
The defining feature of an alcohol is the –OH group.
For example:
methanol
CH3OH
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ethanol
C2H5OH
propan-1-ol
C3H7OH
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Boiling points of alcohols
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Boiling points of alcohols
All molecules are held together by intermolecular forces.
methanol
boiling
These forces must be overcome in order for a
substance to turn into a gas (boil).
The intermolecular forces between alcohol molecules are
relatively strong because the –OH groups attract each other.
Greater amounts of energy are needed to separate the
molecules. This means that alcohols have relatively high
boiling points compared to alkanes of the same length.
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Boiling points: Alcohols vs. alkanes
Boiling points are higher for larger alcohol molecules.
All molecules are weakly attracted to each other. This
attraction is stronger between larger molecules than smaller
ones, so boiling points are usually higher.
pentan-1-ol: b.p. = 138°C
methanol: b.p. = 65°C
This is true of alkanes as well as alcohols – the longer the
carbon chain, the higher the boiling point.
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Investigating boiling points of alcohols
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Reactivity of alcohols
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Reaction of alcohols with oxygen
Because alcohols contain hydrocarbon chains, they often
react in a similar way to alkanes.
For example, ethanol burns in oxygen to form carbon dioxide
and water:
ethanol
+
oxygen

carbon dioxide
+
water
C2H5OH
+
3O2

2CO2
+
3H2O
What is the equation for the reaction of hexane with oxygen?
hexane
+
oxygen

carbon dioxide
+
water
2C6H14
+
19O2

12CO2
+
14H2O
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Reactions of alcohols and water
Because alcohols contain an –OH functional group, they
often react in a similar way to water.
For example, ethanol reacts with sodium to form sodium
ethoxide and hydrogen:
ethanol
+
sodium
2C2H5OH
+
2Na
 sodium ethoxide + hydrogen

2C2H5ONa
+
H2
What is the equation for the reaction of water with sodium?
water
+
sodium
2H2O
+
2Na
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 sodium hydroxide + hydrogen

2NaOH
+
H2
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Alcohols: true or false
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Making ethanol
Ethanol is used as a fuel, a solvent, and as a feedstock in
other reactions. It as also found in alcoholic beverages like
beer and whiskey.
Ethanol can be made by
three methods:
 fermentation
 hydration of ethene
 bacterial action on
wood and plant waste.
Each of these methods has
advantages and disadvantages.
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Making ethanol by fermentation
Most ethanol is made from glucose (sugar) by fermentation:
glucose

ethanol
+
carbon dioxide
C6H12O6

2C2H5OH
+
2CO2
The reaction is performed by yeast.
Yeast is a type of fungus. It produces alcohol when it respires
anaerobically. This means respiring without oxygen.
The yeast metabolizes the sugar to make ethanol and
carbon dioxide.
The ethanol produced in the reaction is removed from the
mixture by distillation.
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Making ethanol by fermentation
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Conditions for fermentation – temperature
Temperature:
A temperature range of between 25 °C
and 50 °C is needed for fermentation
to be successful.
What happens to the rate of reaction
at temperatures above and below this
range?
 If the temperature is too low, the
reaction will take place very slowly
as the yeast is less active.
 If the temperature is too high, the
yeast cells are damaged and eventually
killed, bringing the reaction to an end.
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Conditions for fermentation – oxygen
Oxygen:
If oxygen is present in the
mixture, the yeast will respire
aerobically, creating only water
and carbon dioxide.
The presence of oxygen will
also oxidize any ethanol that is
made, to form ethanoic acid.
Under some circumstances
this reaction can be useful, for
example, in turning wine into
vinegar.
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Conditions for fermentation
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Making ethanol from ethene
Ethanol can also be made by reacting ethene with water.
Ethene is mixed with high pressure steam in the presence of
a phosphoric acid catalyst:
C2H4
+
H2O

phosphoric
acid catalyst
CH3CH2OH
Most of the ethanol used as feedstock in the
petrochemical industry is made using this process,
as the reaction is quicker and the product is purer.
However, ethene can be expensive as it comes from crude
oil. High temperatures and pressures are also needed.
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Making ethanol from ethene
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Making ethanol using bacteria
Scientists are working on new ways of producing ethanol.
Bacteria have been genetically to ferment plant cellulose.
Cellulose is a complex
carbohydrate found in the
tough, rigid parts of plants.
Good sources of cellulose
include wood, paper,
grass cutting and wood chippings.
Cellulose comes from the parts of plants which are inedible.
It is found in many materials that are usually thrown away.
At present however, fermenting cellulose using bacteria is
a slow and expensive process.
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Making ethanol: comparing methods
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Which method: you decide
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Using ethanol and methanol
Ethanol is the alcohol that is used
to make alcoholic drinks.
It also has antibiotic properties,
so is often used in antibacterial
hand wipes.
Methanol is used in antifreeze
– a liquid that stops car engines
from freezing in winter.
Methanol and ethanol are widely
used for making other chemicals.
Both are often used as solvents,
to dissolve other chemicals, e.g.
in paints and makeup.
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Using ethanol as a fuel
Bioethanol is an alcohol produced by the natural
fermentation of the carbohydrates in sugar beet,
sugar cane or wheat crops.
‘Flexi-Fuel’ vehicles, fitted
with modified fuel injection
systems, can run on E85 fuel
(85% bioethanol, 15% petrol),
which cuts carbon dioxide
emissions by 70% compared
to normal petrol-engine cars.
What are the advantages and disadvantages of using
bioethanol as a fuel, rather than petrol?
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Using alcohols to make esters
Esters are a group of chemicals used as perfumes and
flavourings. They contain an –COO– functional group:
Esters are made from the reaction of an alcohol with a
carboxylic acid:
carboxylic acid +
alcohol

ester
+
water
+ methanol  methyl +
propanoate
water
For example:
propanoic acid
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Making esters
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Using ethanol to make ethene
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Using ethanol to make ethene
The reaction that produces ethene from ethanol is called a
dehydration reaction, because a molecule of water is
removed from each molecule of ethanol.
ethanol

ethene
+
water
CH3CH2OH

C2H4
+
H2O

+
The reaction needs a high temperature and a catalyst, such
as aluminium oxide to work. Making ethene on an industrial
scale also requires a high pressure.
Why are each of these conditions needed?
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Using alcohols: true or false
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Glossary
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Anagrams
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Multiple-choice quiz
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