1. The alcohols are a homologous series.
Structure of Alcohols
The alcohols are a homologous series.
Alcohols are organic compounds which have the hydroxyl (–OH) functional group.
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2. Structure and Formula of Alcohols
Alcohols have the general formula CnH2n+1OH.
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3. Properties of Alcohols
Alcohols are soluble in water, but their solubility decreases as their molecular size increases.
For example, methanol is very soluble in water but butanol is only slightly soluble in water.
Unlike the alkanes and alkenes, the first four alcohols are liquids at room temperature and pressure.
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4. Properties of Alcohols
Although alcohols contain the –OH group, they are not alkalis. In fact, they are all neutral.
Alcohols can take part in these reactions: combustion and oxidation.
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5. Chemical Property 1 - Combustion
An alcohol burns in air to produce carbon dioxide and water vapour.
heat
ethanol + oxygen → carbon dioxide + water vapour C2H5OH + 3O2 → 2CO H2O
The flame produced is clean.
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6. How is the combustion of alcohols useful to us?
Alcohols can be used as a fuel because:
Methanol is less likely than conventional fuels to explode in an accident.
It is a clean fuel.
When alcoholic beverage is burnt with food, it gives a distinct flavour.
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7. Chemical Property 2 - Oxidation
We can oxidise an alcohol (for example, ethanol) by warming it with acidified potassium dichromate(VI).
C2H5OH + acidified K2Cr2O7
cold water
heat
CH3COOH
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8. Chemical Property 2 - Oxidation
H2O
C2H5OH + acidified K2Cr2O7
cold water
heat
CH3COOH
The colour of potassium dichromate(VI) changes from orange to green.
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9. How is oxidation of alcohol useful?
The police use a breathalyser to test the amount of alcohol consumed by drivers.
A breathalyser contains potassium dichromate(VI).
A colour change is registered if a certain amount of alcohol is present in the breath.
The orange colour changes to green.
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