including the production, properties and uses
See also 9b.
Biofuels, alternative fuels
(now on a separate page)
Brown's GCSE/IGCSE/O Level KS4 science–CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
9a. Alcohols , Ethanol, Properties, Reactions and Uses
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!
The molecular structure and physical properties of ethanol. Some chemical
reactions of ethanol e.g. combustion, dehydration, esterification. These
revision notes on physical properties of alcohols, the industrial production of
ethanol, the chemical reactions of ethanol, the uses of alcohols like ethanol, should prove useful for the
NEW AQA GCSE chemistry,
Edexcel GCSE chemistry & OCR GCSE chemistry (Gateway & 21st Century) GCSE (9–1),
(9-5) & (5-1) science courses.
Index of KS4 Science GCSE/IGCSE/O Level
Chemistry Oil & Organic Chemistry revision notes pages: 1.
Fossil Fuels & carbon Cycle : 2.
Fractional distillation of crude oil & physical
properties and uses of fractions,
what makes a good fuel? : 3.
ALKANES - saturated hydrocarbons, structure, uses, combustion : 4.
Pollution, carbon monoxide, sulfur/nitrogen oxides, climate change-global warming,
carbon footprint :
5. Alkenes - unsaturated hydrocarbons,
structure and chemistry :
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? : 9a. Alcohols,
Ethanol, manufacture, physical properties & chemical reactions
Biofuels & alternative fuels,
hydrogen, biogas, biodiesel
: 10a. Carboxylic
acids - chemistry and uses
: 10b. Esters, chemistry and uses including perfumes
: 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
destruction, CFC's and free
radicals : 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
ALL my Advanced
Level Organic Chemistry revision notes
for more advanced notes on alcohols
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, the homologous series we call alcohols, which
all have the C–OH 'hydroxy' functional
group in their structure.
The full displayed formula for the
first five members of the homologous series of ALCOHOLS
diagrams show ALL the covalent bonds (C-H, C-C, C-O and O-H) in alcohol
The formulae can also be written as:
CH3OH, CH3CH2OH, CH3CH2CH2OH,
CH3CH2CH2CH2OH and CH3CH2CH2CH2CH2OH
(Note: the technical names for the 3rd,
4th and 5th displayed above are propan-1-ol, butan-1-ol and pentan-1-ol)
Methanol, ethanol, propanol and butanol
all colourless flammable liquids that dissolve in water to give neutral solutions (pH
- Ethanol is used as
a solvent, as a
biofuel (can be mixed with petrol or used directly), and used to make 'ethyl esters' (see
Esters page) 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.
- Note that ethanol can be made
from waste biomass (see Biofuels)
- 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 in a reactor vessel (a big vat!). The yeast contains an
enzyme called zymase which acts as the biological catalyst to convert sugar
to ethanol in fermentation, it works best at an optimum of pH ~4.
Under anaerobic conditions at an optimum temperature of 30oC to
40oC, the sugars react via the enzymes in the yeast
cells to form ethanol and carbon dioxide gas ...
- The fermentation reaction of the sugar
obtained from the sugar cane or sugar cane is ...
- glucose (sugar) == enzyme ==> ethanol + carbon
====> 2C2H5OH(aq) + 2CO2(g)
- The carbon dioxide is
allowed to escape and air is prevented from entering the reaction vessel
to stop oxygen oxidising ethanol to ethanoic acid ('acetic acid' or
vinegar!) ensuring the reaction occurs under anaerobic conditions. The
acid would also lower the pH lowering the effectiveness of the enzyme
and it wouldn't do the taste of beer any good either.
- When the reaction is over, the 'yeast
sludge' settles out and the mixture decanted off prior to distillation. Not
sure if the mixture is further filtered before distillation?
How is the ethanol separated from a
- The ethanol is separated from the reaction
mixture by fractional distillation to make a petrol additive fuel
or whisky! Ethanol has a lower boiling point (78oC) than water
(100oC) and distils off first giving a concentration of upto 95%
ethanol. The two vapours separate out in the fractionating column, the lower
boiling ethanol rising to the top, passing out into the condenser,
condensing to a liquid for collection in some suitable container. Most of
the water condenses back into a liquid in the fractionating column and runs
back into the flask. This distillation is needed to make spirits like brandy
and whisky. The laboratory process is illustrated in the diagram on
the right using a glass column filled with glass beads and connected to the
distillation flask and a Liebig condenser (see
separation of mixtures -
distillation for more explanation).
- Extra notes on the fermentation
- 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.
- When the concentration of alcohol
reaches about 10–20% the fermentation reaction stops because the yeast
cells are then killed by this high concentration of ethanol.
ethanol is classed as a toxic poison just like cyanide and arsenic!
- Its important to have the optimum
temperature (30oC – 40oC) otherwise the efficiency
of the process is affected. If the temperature is to high the enzymes in
the yeast cells are denatured and if the temperature is too low, the
reaction is too slow (see graph of rate of reaction below).
graphically illustrates the idea of the optimum temperature by showing
the rate of reaction varies for a fermentation process.
graphically illustrates the idea of the enzyme zymase working best at
around a pH of 4. In very acid or moderate to strong alkaline conditions
the zymase enzyme becomes very ineffective and the rate of reaction for
fermentation becomes extremely slow, inefficient and uneconomic (same
argument for temperature too).
details about enzymes see
in a solution made from
fermented sugar cane or sugar beet, can be concentrated by fractional distillation.
- The fermentation process is used to make
wines and beers for the food and drinks industry. Brandy is made from
distilling wine to concentrate the alcohol. Whisky is distilled from
fermented grain (e.g. barley) and vodka is distilled from fermented
grain or potatoes. Beers typically have 3–4% ethanol, most wines in the
supermarket seem to be ~15% and spirits may have a concentration of upto
- In Brazil ethanol is blended with petrol to give an alternative motor
vehicle fuel (gasohol) i.e. an example of a biofuel.
See also 9b.
- C2H5OH(l) +
3O2(g) ====> 2CO2(g) + 3H2O(l) +
heat energy from the exothermic reaction
- You produce various blends of petrol by
mixing ethanol from fermentation with petrol from the fractions of
distilled crude oil.
- 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.
- The social and medical issues associated
with drinking alcoholic beverages
('alcohol') is the major ingredient in the drinks industry producing
beers, wines and spirits from fermentation processes.
- Ethanol has a powerful physiological
effect on the body, particularly the brain.
- Alcohol containing drinks initially make
you feel relaxed and less inhibited.
- However, there are health and social issues
about the medical and behavioural aspects of alcohol consumption e.g.
- Ethanol reduces brain activity e.g.
slower thinking and slower reaction responses to a changing situation
hence the obvious dangers from drink driving! Many serious injuries and
deaths result from 'drink driving' accidents.
- Your judgement is impaired and your
general physical coordination, including balance, are much affected.
- Imbibing large quantities of alcohol can
produce unconsciousness and a potentially fatal coma.
- Alcohol causes dehydration and brain
cell damage leading to decrease in brain function and long–term memory
- Alcohol causes liver damage and a very
serious condition, a liver disease called cirrhosis of the liver, you
may even need a liver transplant if lucky enough to obtain one if your
liver eventually fails to function.
- and addiction problems
adding unnecessary extra costs for the NHS (in the UK).
- Binge drinking and
alcohol dependency, especially among young people, can cause major social problems both within a family
and for the wider community with anti–social behaviour. This again cost
society in policing and doctors in A & E.
- Drinking too much can lead to
violent behaviour, silly and sometimes dangerous 'loutish'
- Alcoholism can lead to family
breakdown, loss of job and eventually homelessness.
- Irresponsible sexual behaviour
ranging from not using contraception, increasing chance of pregnancy
or passing on sexually transmitted diseases to the worst case
- Liver disease from alcohol abuse is now
showing up in young men and women in their 20s, but there are plenty of
older people drinking to much too.
- Just out of interest, doc b is
actually allergic to alcohol and can become quite ill after one
drink! maybe its a blessing? maybe not!, but I'm very relaxed and
relatively unstressed in my retirement and thoroughly enjoying to
continue to write this website without the need of either relaxants
- Methylated spirit is
mainly ethanol but
poisonous and nasty tasting chemicals like methanol
are added so it is not used as a
- Deaths have occurred from drinking
'meths' and from contaminated illicit alcoholic drinks.
- Ethanol can also be produced by the reaction of
steam and ethene (an alkene from oil cracking)
in the presence of a strong acid catalyst (phosphoric
- The reversible reaction is carried out at a moderately high temperature
(e.g. 300oC) and a
high pressure (e.g. 60–70 times 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.
- This process can be carried out efficiently
and continuously on a large industrial scale to produce high quality ethanol
compared to the slow fermentation process producing impure ethanol (see
- The ethene is obtained from catalytic or
steam cracking reactions at high temperatures of 450oC to 900oC
of alkane hydrocarbons from the fractional distillation of crude oil e.g.
- butane ==> ethane + ethene
- the ethane can be further cracked to make
- ethane ==> ethene + hydrogen
- so you can have, for example, a synthetic
route for ethanol as follows ...
- crude oil ====> ethane ====> ethene ====>
- Note that ethanol made from ethene is NOT a
renewable method of alcohol production because ethene is made from cracking
hydrocarbons from crude oil. Ethanol from plant material like sugar cane or
sugar beet can be considered renewable.
- Advantages and disadvantages of the two
methods of making ethanol
- We are talking fermentation and hydration of
ethene and the 'pros' and 'cons' of the ways of making
- See also 9b.
- BUT first for instance, are the two methods
of ethanol production 'green' and 'sustainable'
- Factors to consider include listed
which you can merge in with the 'pros' and 'cons' discussion that
- What is the source of raw material? Will
it run out?
- Fermentation: Sugar beet and sugar cane grow quickly,
particularly in warm climates and labour may be very cheap in third
world countries. So we have a sustainable renewable resource thanks to
- Cracking & ethene hydration: Crude
oil, from which ethene is obtained by cracking, will eventually run
out, and oil is a non-renewable resource, so not sustainable in the
- What are the energy costs? and catalyst
- Fermentation: Some energy is required to keep the
fermenting mixture at the optimum temperature of 30-40oC.
Yeast is relatively cheap to produce, since it reproduces and grows
- Cracking & ethene hydration: Both
processes need energy to sustain high pressure and high temperature
reaction conditions. There is also an extra cost for catalysts which
would cost a lot more than yeast.
- Are there any implications for climate
change? Are there any environmental issues?
- Fermentation: Carbon dioxide is produced in the
process, contributing to global warming, but, isn't it recycled via
photosynthesis when more sugar beet or sugar cane is grown?
- Cracking & ethene hydration: Neither
processes directly harms the environment, though there are dangers
from oil spillages in transporting oil in tankers.
- What is the atom economy? Is there much
- Fermentation: The atom economy is only 51% (see
calculation) because 49% by mass of the
sugar is lost as carbon dioxide. Not only that, as the yeast cells are
killed off by the high concentration of ethanol, not all of the sugar is
actually fermented further decreasing the efficiency of the process.
- Cracking & ethene hydration:
Cracking ethane and other hydrocarbons is quite high (93%) with only
hydrogen gas as the waste product (but this can be used in
hydrogenation processes and making ammonia). The atom economy is
very high for the hydration of ethene (theoretically 100% with just
- Is it a profitable process?, does it
make a profitable product?
- Fermentation: It would seem so from the point of view
of the food and drinks industry, breweries and vineyards make good
profits, though a vineyard's economy-profits can be dependent on the
weather. BUT, is it profitable to use the alcohol as a biofuel? e.g.
blended with petrol from oil.
- Cracking & ethene hydration: Both
processes are fast and efficient and can be run on a continuous
basis and at the moment the raw materials, from oil, are relatively
cheap, but the price will increase as oil reserves become depleted
in the future.
- Does the fermentation process have any
issues with society? e.g. are there particular benefits or risks?
- Fermentation: There are no particular health and
safety issues or great risks for the surrounding local communities,
unlike the potential hazards of running an oil refinery. The risks come
later with alcohol abuse! Benefits may include jobs for the local
economy and revenue for local farmers growing the sugar cane or sugar
- Cracking & ethene hydration: There
are important health and safety issues to deal with in the
petrochemical industry. You are dealing with highly flammable and
explosive gases being processed at high temperatures and pressures.
This poses dangers at all the time and so all the processes must be
carefully monitored and controlled, this is also increases the costs
of the processes because it requires very standards of engineering
and safety measures.
- Are there any issue with waste products?
- Fermentation: The waste carbon dioxide can be safely
released into the atmosphere, but it could be used in fizzy carbonated
drinks or even pumped into greenhouses to increase the rate of
photosynthesis - case of good recycling?
- Cracking & ethene hydration: The
only waste product from cracking is hydrogen gas, but this can be
used to hydrogenate vegetable oils to make margarine or reacted with
nitrogen to make ammonia.
- Advantages of
fermentation to make ethanol
- 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 and since based on an
agricultural system, it aught to be sustainable with a long–term
- It is also possible to make a range of
organic chemicals from ethanol itself.
- Disadvantages of
fermentation to make ethanol
- Its a slow
reaction and made by an inefficient batch process, poor quality
product e.g. low aqueous concentration of ethanol. A batch process
means you have to keep on emptying the reaction vessel (e.g.
fermentation vat or tank) and clean it out and refill with reactants
i.e. yeast and sugar solution.
- The yield of the reaction is less
than that from the hydration process.
- The product is not very pure and
expensive purification via fractional distillation is required, and
even that has a limit of 95% purity.
- 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.
- The atom economy is lower than
that from the hydration of ethene.
- atom economy = 100 x mass of
useful products / mass of reactants
- from the equation: C6H12O6
====> 2C2H5OH + 2CO2
- and molecular masses: Mr(glucose)=
180 and Mr(ethanol) = 46, (C = 12, H = 1, O = 16)
- atom economy = 100 x (2 x
46) / 180 = 51% for fermentation
- It is theoretically 100% for the ethene
- 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 hydration of ethene
route to ethanol manufacture
- Its a fast and
efficient continuous process in the petrochemical industry which
produces a relatively pure product in bulk quantities. Its NOT a batch
process, the ethene and water can be rapidly fed into the reactor
chamber and the product collected, such a system may run for months
without any need to replenish the catalyst or carry out maintenance
- 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!
- The product formed is much purer
than that from fermentation and requires less processing to obtain
100% pure ethanol, known as 'absolute alcohol'.
- On the initial pass of the
ethene–water mixture over the catalyst only a small percentage is
converted to ethanol, BUT, it is possible to recycle the unreacted
ethene and so the eventual yield is up to 95%, much higher than the
yield from fermentation.
- The reaction has a higher atom
economy, in fact it is theoretically 100% since the reaction
involves the simple addition of two molecules.
- Disadvantages of hydration of ethene
route to ethanol manufacture
- It uses a non–renewable
finite resource of crude
oil and more costly technology and may not be sustainable in the
- 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.
- In the long term, as oil reserves
decrease, the production of ethene from cracking oil hydrocarbons
may become increasingly costly.
- General notes on
the homologous alcohols and the reactions of alcohols including
- A homologous series is a family of
compounds which have the same general formula and have
a similar molecular structure and similar chemical
properties because they have the same functional group of atoms e.g.
C–OH for an alcohol.
- Members of the alcohol homologous series
have similar physical properties such as
appearance, melting/boiling points, solubility etc. BUT show trends in
them e.g. steady increase in melting/boiling point with increase in carbon
number or molecular mass or in the case of alcohols, they become
progressively less soluble in water.
- It is important to realise that members of a given
homologous series like alcohols have similar chemical reactions
because their molecules contain the same functional group (OH) and so
you can predict the chemical reactions and products of the other
members of the alcohol series
The hydroxy functional group, C–O–H, is
group atoms common to all members of the alcohol homologous series that confer a
particular set of characteristic chemical reactions on each alcohol molecule
of the series.
- The simplest homologous
series of alcohols have the general formula CnH2n+1OH
where n = 1, 2, 3 etc. i.e. the number of carbon atoms in the alcohol
molecule (see the diagram of the first five alcoholism the diagram near the
top of the page).
- You must always make sure the C–O–H group
(OH, hydroxy) is
clear in any molecular structure e.g. displayed formula, you draw of an alcohol
i.e. the C–O–H bonds are clearly shown.
- C2H5OH may not be good
ticks all the boxes!
- 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 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 fourth alcohol, butanol, is quite soluble in water.
- The boiling point steadily rises from one
alcohol to next with increase in molecule size (increase in carbon
number), just like the boiling points rise in alkanes.
- Comparison of alcohols with alkanes
at room temperature and volatility
||Alcohols are colourless
liquids, large alcohol molecules may be white waxy solids. Ethanol
is quite volatile and readily evaporates into the air.
||Colourless gases or
liquids, the first few alkanes methane to butane are gases, the rest
are colourless liquids or white waxy solids.
||Water is a colourless
liquid, but not as volatile as ethanol.
for the same size of molecule (molecular mass) alcohols have a much higher boiling
point than alkanes
||Alcohols have a wide
range from 65oC to over 500oC
ethanol boils at 78oC
|Alkanes have a wide range
from –164oC to over 500oC
Hexane boils at 69oC
is very high for a very small molecule, but since ethanol only boils
at 78oC, the two can be separated by fractional
|Solubility in water
||The first few alcohols
like ethanol are completely soluble (miscible), after that they
become progressively less soluble in water
||All hydrocarbons like
alkanes are insoluble in water
|What will they
||The first few alcohols
are very useful solvents e.g. methanol and ethanol dissolves a wide variety of
compounds including hydrocarbons to some extent, other alcohols,
carboxylic acids and molecules used in the perfume and cosmetic
industries. The important point here is that ethanol will dissolve
many compounds water can't.
||Alkane liquids like
hexane have limited use as solvents, they will dissolve other
hydrocarbons from diesel to waxes, but not much else.
||Water is very useful solvent,
dissolves a wide variety of compounds e.g. lots of salts, some
organic compounds like sugars, smaller alcohols, smaller carboxylic acids
(like ethanoic acid). Water is used
widely in all sorts of domestic products from cosmetics to cleaning
fluids as the main media or solvent.
- As mentioned above, alcohols very
useful 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 because it mixes well with
natural oils (smell 'scent') and water which makes up the bulk of
many cosmetic preparations.
- In these sorts of cosmetic products the aromatic oils and
water base become compatible in the alcohol.
Esters are also used as solvents
- Why does a substance dissolve in
one liquid solvent but not another?
- There are three particle interactions going
on if you mix one substance with another e.g. a liquid solvent that
may or may not dissolve a solid.
- The three possible attractions are (i)
solid ... solid, (ii) solid ... liquid and (iii) liquid ...
- The relative strength of these attractive
intermolecular forces decides whether e.g. a solid will dissolve in a
- For example, nail varnish will not dissolve
in water, but will dissolve in organic solvents like an ester, alcohol or
- Nail varnish is insoluble in water
because the intermolecular forces between the nail varnish molecules
themselves, and between the water molecules themselves are much stronger
than the attraction between water and the nail varnish molecules, so the
nail varnish cannot possibly dissolve in water. Forces (i) and (iii)
override force (ii)
- However, nail varnish will dissolve in
organic solvents like butyl ethanoate or ethyl ethanoate (esters, old
names butyl acetate and ethyl acetate), ethanol ('alcohol')
and propanone (old name acetone) solvents. Here the organic solvent
intermolecular attraction to the nail varnish molecules can override the
nail varnish ... nail varnish and the solvent ... solvent intermolecular
forces and the nail varnish will dissolve. In this case attractive force
(ii) overrides both attractive forces (i) and (iii).
- Since different solvents are different
molecular affinities for different substances, the solubility of a solute in
a solvent can vary quite considerably from one solvent to another.
- The question of which solvent you choose
to use to dissolve a substance depends on two main factors ..
- (a) How soluble is the substance in
- (b) How safe is to use the solvent?
e.g. in terms of inhaling vapour or spillage on the skin (gloves!), is it
harmful?, irritating?, even toxic?, and is it highly flammable, so more
dangerous to use.
- Chlorinated organic solvents e.g.
trichloromethane ('chloroform') tend to be harmful, alcohols and esters are
safer but are more flammable.
- This section
is repeated in esters
Chemical properties of alcohols – important reactions and uses
- The first two alcohols, methanol and
ethanol are important chemical feedstock ('starting materials') for the
manufacture of many other organic chemicals e.g. esters, carboxylic
alcohols 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.
- 'Methylated Spirits' ('meths') is mostly
ethanol with other chemicals added to it like methanol to make it unpalatable to drink,
since pure ethanol is highly poisonous, but meths is more toxic!
- 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 (dealt with in detail on another page)
Ethyl ethanoate, an ester, is formed by the
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 10b. 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 ionic salt
- alcohol + sodium ==> an alkoxide +
- Normal 'hydrogen' gas fizzing is observed
at a moderate rate, and the salt
product is soluble in the alcohol itself e.g.
- ethanol + sodium ====> sodium
ethoxide + hydrogen
- (ii) 2C2H5OH + 2Na
- There is some similarity with the
reaction of sodium with water (Alkali
sodium + water ==> sodium
hydroxide + hydrogen
2Na + 2H2O
2Na+OH– + H2
Both reactions give hydrogen
gas, though the sodium reacts much faster with water. The ethoxide and
hydroxide are similar because on evaporation of the unreacted ethanol or
water, a solid white ionic compound is formed.
It can further be noted that
relatively 'unreactive' alkanes do not react with sodium.
- similarly with other alcohols ...
- (i) methanol + sodium ====> sodium
methoxide + hydrogen
- 2CH3OH + 2Na ====> 2CH3O–Na+
- (iii) propanol + sodium ==> sodium
propoxide + hydrogen
+ 2Na ====> 2CH3CH2CH2O–Na+
- (iv) butanol + sodium ==> sodium
butoxide + hydrogen
+ 2Na ====> 2CH3CH2CH2CH2O–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, note that these aerobic conditions
produce a very different reaction than anaerobic fermentation of sugar.
- ethanol + oxygen ====> ethanoic acid +
- CH3CH2OH + O2
====> CH3COOH + H2O
+ O2 ====>
- This 'natural oxidation' is used to
manufacture vinegar in bulk for the food industry and domestic
consumption in cooking and eating.
- 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.
- Other alcohols can also be oxidised to the
corresponding carboxylic acid e.g.
- propanol + oxygen ====> propanoic acid + water
+ O2 ====> CH3CH2COOH + H2O
- butanol + oxygen ====> butanoic acid + water
+ O2 ====> CH3CH2CH2COOH +
- These reactions require special chemical
reagents, you can't burn them in air to make the carboxylic acid, you
would just make carbon dioxide and water on combustion!
When burned, ethanol, like any alcohol, on
forms carbon dioxide and water
- (ii) ethanol + oxygen ==> carbon dioxide +
- CH3CH2OH(l) +
3O2(g) ====> 2CO2(g) + 3H2O(l)
- As mentioned in section
9b Fuels Survey, ethanol can be
blended with petrol to fuel road vehicles.
- Similarly, but the symbol equations are
more awkward to balance ...
- (i) methanol + oxygen ====> carbon dioxide
- 2CH3OH(l) +
3O2(g) ====> 2CO2(g) + 4H2O(l)
- (iii) propanol + oxygen ====> carbon
dioxide + water
- 2CH3CH2CH2OH(l) +
9O2(g) ====> 6CO2(g) + 8H2O(l)
- (ii) butanol + oxygen ====> carbon dioxide +
- CH3CH2CH2CH2OH(l) +
6O2(g) ====> 4CO2(g) + 5H2O(l)
- As mentioned in section
9b Fuels Survey, ethanol can be
blended with petrol to fuel road vehicles.
- Ethanoic acid (old name 'acetic acid') is the basis of
vinegar and is also used in making esters (e.g. for flavourings like ester pear drop essence
as mentioned above).
Ethanol can be dehydrated to ethene
by passing the alcohol vapour over
heated aluminium oxide catalyst.
- This is actually the reverse of the
reaction by which ethanol is made from ethene from cracking oil.
- ethanol ====> ethene + water
- CH3CH2OH ====>
CH2=CH2 + H2O
- This reaction is potentially an
important source of organic chemicals e.g. plastics made by
polymerising ethene, and from a renewable
resource since the ethanol can be made by fermentation of
- It is being used in countries that do
not have oil reserves but have large areas of agricultural land
producing sugar cane or sugar beet that are the raw materials for the
- The ethanol, so produced, becomes an
important chemical feedstock for producing lots of other chemicals.
- 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
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!
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
ALL my Advanced
Level Organic Chemistry revision notes
for more advanced notes on alcohols
keywords equations: C6H12O6 ==> 2C2H5OH + 2CO2 * C2H5OH
+ 3O2 ==> 2CO2 + 3H2O * CH2=CH2 + H2O ==> CH3CH2OH (or C2H5OH)
Revision notes on ethanol physical
properties chemical reactions KS4 Science
GCSE/IGCSE/O level Chemistry Information on ethanol physical properties chemical
reactions for revising for AQA GCSE
Science, Edexcel Science chemistry IGCSE Chemistry notes on ethanol physical
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Science, OCR Gateway Science notes on ethanol physical properties chemical
reactions WJEC gcse science chemistry notes on
ethanol physical properties chemical reactions CIE O Level chemistry CIE IGCSE chemistry notes on
ethanol physical properties chemical reactions CCEA/CEA gcse science
chemistry (help for courses equal to US grade 8, grade 9 grade 10) science
chemistry courses revision guides explanation chemical equations for ethanol
physical properties chemical reactions
educational videos on ethanol physical properties chemical reactions guidebooks for revising
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