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Alcohols

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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 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