Brown's GCSE/IGCSE/O Level KS4 science–CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
9. Alcohols , Ethanol, Properties, Reactions and Uses, Biofuels
What we call 'alcohol' actually
has the proper chemical name ethanol and belongs to a group of organic molecules
called alcohols? How do we make ethanol? Why has it been manufactured for
thousands of years? How is ethanol made in industry? What is ethanol used for? All of these questions are answered below!
Index of KS4 Science GCSE/IGCSE
Chemistry Oil & Organic Chemistry Pages: 1.
Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3.
ALKANES – saturated hydrocarbons and combustion : 4.
Pollution, carbon monoxide, nitrogen oxides, what
makes a good fuel?, climate change–global warming :
5. Alkenes – unsaturated hydrocarbons :
6. Cracking – a problem of supply and demand, other products :
7. Polymers, plastics, uses and problems :
8. Introduction to Organic Chemistry – Why so many series of
organic compounds? : 9. Alcohols – Ethanol
– properties, reactions, biofuels :
10. Carboxylic acids and esters : 11. Condensation polymers, Nylon & Terylene,
comparing thermoplastics, fibres and thermosets
12. Natural Molecules – carbohydrates – sugars
– starch : 13. Amino acids, proteins,
enzymes & chromatography : 14. Oils, fats,
margarine and soaps :
15. Vitamins, drugs–analgesic medicines & food
additives and aspects of cooking chemistry! : 16. Ozone, CFC's and free
radicals : 17. Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice and Gap–Fill Quizzes:
m/c QUIZ on Oil Products (GCSE/IGCSE easier–foundation–level)
m/c QUIZ on Oil Products (GCSE/IGCSE harder–higher–level) :
IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry
3 Easy linked GCSE/IGCSE Oil Products word–fill worksheets
What is ethanol and how
can we make it?
The 'alcohol' of the homologous series of alcohols!
What we call alcohol in everyday life is a
substance whose chemical name is ethanol. Ethanol is just one member of
a family of substances called alcohols which have a C–OH functional
group in their structure.
which contains the
alcohol group –OH is a sterol, a sub–group of organic molecules called
steroids (BUT not the body building type of steroid!, more to do with
the metabolism of fats!). Cholesterol is an essential steroid–sterol to humans but if
too much is produced it can cause heart disease. The
image on the right gives the skeletal formula structure of cholesterol
structure representation is usually only dealt with at advanced level). All the lines in the structure
represent bonds between carbon atoms except the 'wedge dash' to the –OH alcohol
group in the bottom left of the molecule. Also note the 'alkene' double
bond functional group to the right of the –OH group. So, even at advanced
level, the same organic functional groups crop up!
ETHANOL: Ethanol structure
- Ethanol is used as
a solvent, as a
bio–fuel (can be mixed with petrol or used directly), and used to make 'ethyl esters' (see
below) as well as the 'potent' chemical present in alcoholic
- The % alcohol in wines, spirits and
beer varies from 1–40%.
- The alcohol (ethanol) used in
beer and wines is made by fermentation, NOT from ethene derived
from cracking crude oil.
- The fermentation chemistry to
produce alcoholic drinks is outlined below.
- There are health and social issues
about the medical and behavioural aspects of alcohol consumption.
Alcohol causes liver damage and addiction problems.
- Binge drinking and
alcohol dependency can cause major social problems both within a family
and for the wider community.
- Methylated spirit
mainly ethanol but
poisonous and nasty tasting chemicals like methanol
are added so it is not used as a
- Ethanol can be produced by fermentation of
sugars. The raw material sugar
(from sugar cane or sugar beet) is mixed with water and yeast at just above
room temperature. The yeast contains enzymes which are biological catalysts.
The sugars react to form ethanol and carbon dioxide. The carbon dioxide is
allowed to escape and air is prevented from entering the reaction vessel
to stop oxidation of ethanol to ethanoic acid ('acetic acid' or
When the reaction is over the ethanol is separated from the reaction
mixture by fractional distillation to make a petrol additive fuel
- e.g. glucose (sugar) == enzyme ==> ethanol + carbon
==> 2C2H5OH(aq) + 2CO2(g)
- The progress of the fermentation
can be followed by measuring the density of the fermented liquid with a
hydrometer. Ethanol/alcohol is less dense than water/sugar so the
density changes as the sugar is converted into alcohol.
in a solution made from
fermented sugar cane, can be concentrated by fractional distillation.
- In Brazil it is blended with petrol to give an alternative motor
vehicle fuel (gasohol) i.e. an example of a bio–fuel.
- C2H5OH(l) +
3O2(g) ==> 2CO2(g) + 3H2O(l) +
heat energy from the exothermic reaction
- The natural fermentation process would
have discovered by accident after its products were sampled and so beer
has been brewed for thousands of years. Most people in medieval times
would have drunk weak beer every day because it was less harmful than
polluted water supplies apart from pure natural spring water.
- Ethanol can also be produced by the reaction of
steam and ethene (from oil cracking)
in the presence of a strong acid catalyst (Phosphoric
acid). The reversible reaction is carried out at a moderately high temperature
(e.g. 300oC) and a
high pressure (e.g. 60 x atmospheric pressure). The higher temperature and catalyst
speed up the reaction and increasing pressure moves the equilibrium to the
right (side least gaseous molecules at 300oC)
ethene + water
- CH2=CH2 + H2O
==> CH3CH2OH (or C2H5OH)
- This is an example of an alkene
addition reaction and a hydration reaction because it
involves the addition of water to another molecule.
- Advantages and disadvantages of the two
methods of making ethanol
Plus a discussion on biofuels and using plant materials for fuels
- What is a biofuel? What does 'carbon
- Biofuels are alternative fuels to fossil
fuels produced from plant material.
- Ideally they are 'carbon neutral',
that is the carbon dioxide the they give off on combustion is matched by
the plant absorbing the same amount of carbon dioxide. The absorbed
carbon dioxide is then utilised in photosynthesis to regenerate the
plant material ie remaking the same amount of biofuel again. So, its a
sort of mini–carbon cycle.
- Renewable Biofuels that can be burned to heat water
to make steam to drive a turbine and generator. Biofuels are renewable
energy sources and come in a variety of forms eg woodchips (trees or
waste from timber products), alcohol (ethanol
from fermenting sugar cane), biodiesel (from vegetable oil) and
biogas (methane from anaerobic digestion of sewage waste) and are all
derived from plant materials eg crops or bacterial digestion/decay of
waste organic material. The theoretical 'carbon neutral' idea behind
using biofuels is that the carbon dioxide released on burning is
re–absorbed by plants and utilised in photosynthesis to create the next
fuel crop. But, even though this sounds fine in principle, there are
still environmental issues eg in Brazil and other countries, huge areas
of ecological valuable natural rain forest (habitats, species rich) are
being cut down to grow crops for biofuels.
- Ethanol is an example of a renewable
biofuel from plant material.
- What is 'gasohol'? Ethanol and
petrol can be mixed to make a motor vehicle fuel
- Countries like Brazil, that have no oil
reserves of their own, and importing oil is costly, so they are very
interested in the manufacture of biofuels, i.e. fuels that can be
derived from plant crop materials.
- Some ethanol is used in blends of petrol
( a 'gasohol') eg in Brazil (called 'alcool') with
a cheap labour force (local population or migrant labour) and large land
areas growing sugar cane.
- A typical composition of 'gasohol' might
be 10% ethanol (ethyl alcohol) and 90% unleaded petrol (gasoline).
- It is less polluting than ordinary
petrol, it burns more cleanly-efficiently.
- It also makes the imported oil go a bit
- The renewable sugar cane crop is crushed and the sugar
extracted with hot water and the solution fermented with yeast.
- The alcohol is fractionally distilled
from the filtered fermented solution and can then be used as a biofuel.
- Making renewable fuels like
bioethanol from plant materials
- Benefits of using plant materials
- Naturally, they are all renewable.
- Drawbacks and risks to using plant
materials to produce fuels
- Large areas of agricultural land or
- Slow growth eg trees for wood fuels,
fast to burn! could demand be matched?,
- or slow industrial processes like
- Advantages of
- In third world
countries and more advanced developing countries sugar cane/sugar beet
is a common crop and labour
is cheap and
the process uses a cheap renewable resource eg sugar cane grown
in Brazil or sugar beet in England.
- It does not require any advanced
technology compared to a large petrochemical complex based on crude oil.
- It does not require the importation of
expensive crude oil, a non–renewable resource.
- It is also possible to make a range of
organic chemicals from ethanol itself.
- Disadvantages of
- Its a slow
reaction and made by an inefficient batch process, poor quality
product e.g. low aqueous concentration of ethanol.
- The resulting
ethanol/alcohol solution is not very concentrated.
- It only has 4–10%, rest water and waste products e.g. other organic chemicals formed
to, and yeast cell residues to remove.
- Therefore the alcohol must be
distilled from the fermentation mixture, so this purification is an
extra costly process requiring
lots of energy.
- Large areas of agricultural land
are needed and tends towards monoculture agriculture (lack of diversity)
– in many countries
more food should be grown.
- Brazil has allowed the cutting down of large
areas of valuable rain forest.
- Therefore, producing ethanol in this way
does have quite an environmental impact.
- Advantages of ethene
- Its a fast and
efficient continuous process in the petrochemical industry which
produces a relatively pure product in bulk quantities.
- Some countries may
have local oil supply (e.g. North Sea for UK, US and Middle East countries).
- It is much cheaper to produce ethanol
from ethene derived from cracking crude oil fractions compared to any
plant material and fermentation – oil is still relatively cheap, even if
it doesn't seem so when petrol prices go up!
- Disadvantages of ethene
- It uses a non–renewable
finite resource of crude
oil and more costly technology.
- Most countries have to import the crude
oil to make ethene from cracking – supply may be subject to world market
prices or politically unstable situations eg in the Middle East.
- Biodiesel is another biofuel
derived from plant material.
- Biodiesel can be made from vegetable oil
(and animal fat or waste cooking oil) which contain glycerol esters of
long–chain fatty acids.
- These oils/fats like rapeseed oil and
soybean oil can re–esterified
(transesterification) into methyl esters to make a fuel that can be used
directly as diesel fuel or mixed with regular diesel fuel.
- Vegetable oils are suitable for diesel
fuel and release lots of energy on combustion just like petrol or
- Biodiesel has similar physical and
chemical properties to ordinary diesel from crude oil and burns in
conventional diesel engines.
- The simple word equation for processing
vegetable oil into biodiesel fuel is ...
- oil/fat + methanol ==> biodiesel +
- glycerol ester + methanol (an alcohol)
==> methyl ester + glycerol (another sort of alcohol)
- Pros – advantages of using
- Biodiesel, is in theory, another 'carbon
neutral' renewable fuel.
- Biodiesel is readily biodegradable, so
less harmful to the environment if spilled compared to hydrocarbon oils
which take much longer to break down.
- Existing diesel engines don't need
- Cons – disadvantages of using
- Its relatively expensive to make
(small scale production compared to the petrochemical industry based on
- There won't be enough to replace
diesel from crude oil.
- Farmers (especially in third world
countries) may switch from essential food production to producing
plant oils to make biodiesel, thereby increasing food prices and maybe
creating food shortages.
- 'Alternative fuels'
resources, storage and use of the fuels, their products of combustion.
- Ethanol is one of the more recent 'alternative
fuels' to traditional fossil fuels like coal, gas and oil.
- If an efficient source of hydrogen
production could be found, this could be another fuel.
two alternatives to vehicle fossil fuels – their 'pros' and
FUEL (both renewable in theory)
Advantages of the fuel 'pros'
Disadvantages of the fuel 'cons'
Can be cheaply produced from sugar cane/beet
b) Easily stored and distributed as
a liquid fuel.
c) carbon neutral
d) only products are carbon dioxide
and water with no pollutants like sulfur dioxide
Slow rate of mass production
b) Requires large areas of
agricultural land or woodland AND farmers may switch from
growing food crops – increasing food prices and possible causing
food shortages in third world countries.
c) Does produce the greenhouse
gas carbon dioxide (and water), theoretically reabsorbed by
plants, but fast to burn and plants slow to grow.
d) Ethanol fuels are not widely
e) Car engines
need modifying to work with ethanol fuels.
f) Ethanol costs five times more to
produce than 'straight–run' gasoline (and hydrogen is even more
Endless supply of water
Water is the only product of burning hydrogen, so its very clean
use of hydrogen in fuels cells
Efficient large scale technology not yet developed to produce
hydrogen on a large scale eg from electrolysis
using solar power electricity – photovoltaic power system, wind
turbines or hydroelectric power.
b) Although water is cheap and
plentiful, it requires expensive electrical energy to
electrolyse water to split it into hydrogen and oxygen.
c) As a gas it is more difficult to
store, needs a larger storage space (volume) and distribute safely due to it being highly flammable,
easily ignited, so risk of explosion if leaked.
d) You need a special expensive?
hydrogen burning car engine that is not widely available.
e) Hydrogen is an explosive gas and
difficult to store and transport safely from the point of view
of distribution to consumers.
f) Most hydrogen used in industry is
actually made from fossil fuel hydrocarbons! (see making
hydrogen for the
Haber Synthesis of ammonia).
Extra general notes on alcohols and the reactions of alcohols including
- The alcohols form a homologous series with
the same functional group C–O–H. It is the presence of this functional group that
gives alcohols their characteristic properties.
- The simplest homologous
series of alcohols have the general formula CnH2n+1OH
- You must always make sure the OH group is
clear in any molecular structure you draw of an alcohol.
- The last alcohol structure given below is
the full displayed formula which you should definitely know, but you
also need to know the various abbreviated ways of writing the molecular
structure of alcohols.
- The simplest
alcohol with the
lowest carbon number of one is methanol (the 1st in the homologous
series of alcohols is shown below, followed by the next four in the series.
- Ethanol, discussed in detail above,
is the 2nd in the series,
next three are propanol (strictly speaking propan–1–ol, 3rd in series),
butanol (strictly speaking butan–1–ol, 4th in series) and pentanol
(strictly speaking pentan–1–ol, 5th in series), note all the alcohol names end in ...ol, which means the
molecule is an alcohol. The –1–ol means the OH group is on the first
carbon atom of the molecule's chain –C–C– etc.
Physical and chemical properties of alcohols and their uses
- All the alcohols are colourless liquids with a characteristic
- The first three alcohols dissolve in water
(miscible) but as the carbon chain grows longer,, they become less and less
soluble in water.
- The boiling point steadily rises from one
alcohol to next with increase in molecule size (increase in carbon
- They all behave chemically in the
same way (same functional group C–OH) e.g. they all reaction with
sodium, they all react with carboxylic acids to form esters.
- All alcohols are flammable and readily burn
when ignited in air.
- Alcohols are used as solvents – they
dissolve a wide range of compounds, some that water dissolves, but others
like oils, fats and hydrocarbons dissolve in alcohols, which are insoluble
- Ethanol is used as a solvent in cosmetic
products like perfumes and aftershave lotions.
- In these products the aromatic oils and
water base become compatible in the alcohol.
- 'Methylated Spirits' ('meths') is mostly
ethanol with other chemicals added to it to make it unpalatable to drink,
since pure ethanol is highly poisonous.
- A purple dye is added so you don't drink it
- Methylated sprits is used as a fuel in
camping cooker burners (spirit burners - combustion use) and for cleaning
paint brushes (solvent use).
- Its use as fuel for cars was discussed
further up the page.
- Details of the reactions of alcohols are
short note on
Esters are another homologous
series of organic compounds
Ethyl ethanoate, an ester, is formed by the reaction
of carboxylic acid and an alcohol e.g.
- ethanoic acid + ethanol
ethyl ethanoate + water
- sometimes more simply written as
- CH3COOH + CH3CH2OH
CH3COOCH2CH3 + H2O
- General word equation: carboxylic acid + alcohol ==>
ester + water
- Esters are used in perfumes and
food flavourings. Lots of details
in section 10. for the ..
Procedure for preparing
an ester, uses of esters, details of esters & carboxylic acids
Alcohols react with sodium to form
hydrogen and an alkoxide
- alcohol + sodium ==> an alkoxide +
- Normal 'hydrogen' gas fizzing is observed and the salt
product is soluble in the alcohol itself e.g.
- ethanol + sodium ==> sodium
ethoxide + hydrogen
- 2C2H5OH + 2Na ==> 2C2H5O–Na+
- similarly ...
- methanol + sodium ==> sodium
methoxide + hydrogen
- 2CH3OH + 2Na ==> 2CH3O–Na+
- and ...
- propanol + sodium ==> sodium
propoxide + hydrogen
+ 2Na ==> 2CH3CH2CH2O–Na+
Ethanol can be oxidised to form
- Which is a useful organic chemical. BUT it is this oxidation of ethanol that results in alcoholic drinks
turning sour (e.g. cider, wine) when exposed to air!
- The fruit material
already contains the enzymes that catalyse the oxidation of ethanol
('alcohol') in the presence of air.
- ethanol + oxygen ==> ethanoic acid +
- CH3CH2OH + O2
==> CH3COOH + H2O
+ O2 ==>
- This oxidation can also be done in the
heating the ethanol with a mixture of sulphuric acid and potassium
- This is a complex reaction and the mixture turns from orange to green
as the ethanol is oxidised.
- In industry you can oxidise ethanol
directly with oxygen on a large scale.
- When burned, ethanol, like any alcohol, on
forms carbon dioxide and water
- ethanol + oxygen ==> carbon dioxide +
- CH3CH2OH(l) +
3O2(g) ==> 2CO2(g) + 3H2O(l)
- Similarly, but the symbol equations are
more awkward to balance ...
- methanol + oxygen ==> carbon dioxide
- 2CH3OH(l) +
3O2(g) ==> 2CO2(g) + 4H2O(l)
- and ...
- propanol + oxygen ==> carbon dioxide
- 2CH3CH2CH2OH(l) +
9O2(g) ==> 6CO2(g) + 8H2O(l)
- a bit much to balance at GCSE level!,
don't worry about it!
- Ethanoic acid (old name 'acetic acid') is the basis of
vinegar and is also used in making esters (e.g. for flavourings like pear drop essence
as mentioned above).
Ethanol can be dehydrated to ethene
by passing the alcohol vapour over
heated aluminium oxide catalyst.
- ethanol ===> ethene + water
- CH3CH2OH ===>
CH2=CH2 + H2O
- This reaction is potentially an
important source of organic chemicals e.g. plastics from a renewable
resource since the ethanol can be made by fermentation of
- Alcohols from propanol upwards,
carbon number 3 or greater, will form isomers.
- Isomers are molecules with the same
molecular formula but the atoms can be arranged in two or more different
ways e.g. there are two propanols with the molecular formula C3H8O
- they are similar physically and
chemically, but they are not identical.
- You will find plenty of examples on the
Advanced organic chemistry
page for alcohols
image from NIST]
Multiple Choice Quizzes and Worksheets
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry
3 linked easy Oil Products gap–fill quiz worksheets
ALSO gap–fill ('word–fill') exercises
originally written for ...
... AQA GCSE Science
Useful products from
crude oil AND
... OCR 21st C GCSE Science
Worksheet gap–fill C1.1c Air
pollutants etc ...
... Edexcel 360 GCSE Science
Crude Oil and its Fractional distillation
... each set are interlinked,
so clicking on one of the above leads to a sequence of several quizzes
Level Organic Chemistry revision notes
keywords equations: C6H12O6 ==> 2C2H5OH + 2CO2 * C2H5OH
+ 3O2 ==> 2CO2 + 3H2O * CH2=CH2 + H2O ==> CH3CH2OH (or C2H5OH)
Notes information to help revise
KS4 Science Additional Science Triple Award Separate Sciences Chemistry revision
notes for GCSE/IGCSE/O level Chemistry Revision–Information Study Notes for
revising AQA GCSE Science AQA GCSE Chemistry, Edexcel
GCSE Science, Edexcel GCSE Chemistry, OCR 21st Century Science Chemistry, OCR Gateway Science
GCSE science–chemistry CCEA/CEA GCSE science–chemistry
(and courses equal to US grades 8, 9, 10)
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