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© Boardworks Ltd 20121 of 23
Alcohols
2 of 23 © Boardworks Ltd 2012
© Boardworks Ltd 20123 of 23
What are alcohols?
Alcohols are a family of organic compounds that contain
carbon, hydrogen and oxygen atoms.
The defining feature of alcohols is the functional group –OH.
For example:
methanol
CH3OH
propan-1-ol
C3H7OH
ethanol
C2H5OH
They are not hydrocarbons, because they contain oxygen.
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Naming alcohols
The general formula of alcohols is CnH2n+1OH.
CH3OH
C2H5OH
C3H7OH
C4H9OH
methanol
ethanol
propanol
butanol
1
2
3
4
number of carbons name of alcohol chemical formula
Alcohols are a homologous series.
Can you work out the general formula for alcohols?
The name of an alcohol is derived from the number
of carbon atoms in the compound and ends with –ol.
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Finding the formula
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Identifying alcohols
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Boiling points of alcohols
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Intermolecular forces
All molecules are held together by intermolecular forces.
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.
methanolboiling
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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.
ethanol carbon dioxide wateroxygen+ +
C2H5OH 2CO2 3H2O3O2+ +
What is the equation for the reaction of hexane with oxygen?
For example, ethanol burns in oxygen to form carbon dioxide
and water:
hexane carbon dioxide wateroxygen+ +
2C6H14 12CO2 14H2O19O2+ +
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Reaction of alcohols with sodium
Because alcohols contain an –OH functional group, they
often react in a similar way to water.
ethanol sodium ethoxide hydrogensodium+ +
2C2H5OH 2C2H5ONa H22Na+ +
What is the equation for the reaction of water with sodium?
For example, ethanol reacts with sodium to form sodium
ethoxide and hydrogen:
water sodium hydroxide hydrogensodium+ +
2H2O 2NaOH H22Na+ +
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Solubility in water
The solubility of alcohols in water is affected by both the
–OH functional group and the hydrocarbon chain.
interacts with
water molecules
to form new
intermolecular
bonds.
The –OH functional group enables small alcohols to fully
dissolve in water to form a neutral solution. The larger
alcohols have longer hydrocarbon chains, and are therefore
less soluble in water.
opposes
interaction
with water
molecules
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Uses of ethanol
Ethanol is the alcohol that is used to make alcoholic drinks.
Ethanol also has antibiotic
properties, so is often used
in antibacterial hand wipes.
Alcohols have a wide variety of uses, with different alcohols
being better suited to some uses than others.
Alcoholic drinks vary in the percentage
of ethanol that they contain.
Why is ethanol used for alcoholic
drinks rather than a different type
of alcohol?
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Using ethanol as a fuel
Ethanol can be used as a fuel for cars and other vehicles.
What are the advantages and disadvantages of using
bioethanol as a fuel?
Bioethanol is produced by
the natural fermentation of the
carbohydrates in sugar beet,
sugar cane or wheat crops.
Bioethanol is sold as E85 fuel,
which contains 85% bioethanol
and 15% petrol. It can be used
by cars that have modified fuel
systems, and reduces carbon
dioxide emissions by 70%.
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Production of vinegar
Vinegar can also be used as
a food preservative.
Ethanol can be oxidized to make ethanoic acid, which is the
main acid present in vinegar. Vinegar is a dilute solution of
ethanoic acid.
Vinegar is used as a flavouring for
food, for example, in salad dressing.
Ethanoic acid can be made from ethanol
by naturally occurring microbes. If a bottle
of wine is left open for several days it will
begin to change into vinegar.
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Uses of methanol
Alcohols are often used as
solvents in paint. They boil at
a lower temperature than water,
so they evaporate quickly to
leave the dry pigment behind.
Methanol is a commonly used
solvent. Alcohols make useful
solvents because the –OH group
causes part of the molecule to
have a slight positive charge and
part to have a slight negative
charge. This means that ionic
compounds will dissolve in them.
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Using alcohols
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Alcohols: true or false?
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Glossary
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Multiple-choice quiz
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