Alcohols

Physical properties

When comparing alcohols with alkanes containing the same number of carbon atoms alcohols are less volatile, have higher melting points and greater water solubility than the corresponding alkanes.
Differences become much smaller as the length of the carbon chain increases.
Alcohols have polar O-H bonds because of the difference in the electronegativity of the oxygen and hydrogen atoms therefore the alcohols are polar.
The intermolecular forces will be very weak but there will also be much stronger hydrogen bonds.
Hydrogen bonds require large amounts of energy to overcome them so alcohols have high melting points.
Alcohols are soluble in water as the polar OH group can form hydrogen bonds with the water molecule.

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Alcohols burn completely in a plentiful supply of oxygen to produce carbon dioxide and water.
The reaction is exothermic releasing a large quantity of energy in the form of heat.

C2H5OH + 3O2 ---> 2CO2 + 3H2O

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On gentle heating of alcohols under distillation with acidified potassium dichromate, an aldehyde is formed.
If the primary alcohol is heated strongly under reflux with an excess of potassium dichromate a carboxylic acid is formed.

C4H9OH + [O] ---> C4H8O + H2O

Butan-1-ol + oxidising agent ---> butanal + water

C4H9OH + 2[O] ---> C3H7COOH + H2O

Butan-1-ol + oxidising agent ---> butanoic acid + water

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Secondary alcohols are heated under reflux to form ketones.
It is not possible to further oxidise ketones using acidified potassium dichromate.

C3H7OH + [O] ---> C3H6O + H2O

Propan-2-ol + oxidising agent ---> Propanone

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Alcohols are heated under reflux in the presence of an acid catalyst such as concentrated sulfuric acid or concentrated phosphoric acid.
Produces an alkene.
It is an example of an elimination reaction.

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C3H7OH + HBr ---> C3H7Br + H2O

Propan-2-ol + hydrogenbromide ---> 2-bromopropane + water

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