From onlinetuition.com

1. Preparing alcohols
Alcohols can be prepared by using 2
methods :-
a.Hydration of alkene
b. Fermentation
Hydration of Alkene
1.When we discuss the chemical properties
of alkenes, we have learned that, when
alkenes undergo addition reaction with
steam, alcohol will be produced. (see
hydration of alkenes).
2.Equations below shows the hydration of
ethene and propene to produce ethanol
and propanol respectively.
Hydration of Ethene
C2H4 + H2O → C2H5OH

2. Hydration of Propene
C3H6 + H2O → C3H7OH
Fermentation
1.This method only applies to ethanol
2. Fermentation is the chemical process
which microorganism such as yeastact
on carbohydrate to produce ethanol and
carbon dioxide.
2.When yeast is added to sugar (example:
glucose), fermentation occurs. During
fermentation, the yeast produce an
enzyme called zymase. The zymase
enzyme breaks down the glucose
molecules to simpler molecule, namely
ethanol and carbon dioxide.
C6H12O6→2C2H5OH+2CO2

3. 3. Yeast is killed by ethanol concentrations
in excess of about 15%, and that limits
the purity of the ethanol that can be
produced.

4. Physical properties of alcohol
Boiling Points
1. The boiling point of an alcohol is always
much higher than that of the alkane with the
same number of carbon atoms.
2. This is because, the presence of the
hydroxyl group gives extra force between
the molecules, hence more heat energy is
needed to overcome the intermolecular
force when boiling.
3. The boiling points of the alcohols
increase as the number of carbon atoms
increases.

5. 4. This can be explained by the following:
a.number of carbon increases, size of
the molecule increases.
b.intermolecular force increases.
c.more heat energy is needed to
overcome the intermolecular force.
Solubility of Alcohols in Water
1. The small alcohols are completely
soluble in water.

6. 2. However, solubility decreases as the
length of the hydrocarbon chain in the
alcohol increases.
3. Explanation:
a. Every alcohol consists of two parts,
the hydrocarbon chain which is not
soluble in water, and the hydroxyl
functional group, which is soluble in
water.
b. In short chain alcohol, the hydroxyl
group plays a major part in forming
forces (hydrogen bond) in between
water and alcohol molecule, therefore
they are soluble in water.
c. For the long chain alcohol, the
hydroxyl group is just a small part of
the molecule. Therefore, the insoluble
long hydrocarbon chain contribute
more to the forces in between water

7. and alcohol molecule, causes the
solubility
CHEMICAL PROPERTIES OF ALCOHOLS
COMBUSTION
1. As the hydrocarbon, alcohols undergo
combustion with the presence of oxygen to
produce carbon dioxide and water.
2. Combustion of alcohol producesless
sootcompare to combustion of alkanes and
alkenes due to the present of oxygen in the
–OH group.
3.Owing to the presence of the –OH group,
the percentage of carbon in alcohol is
relatively low when compare with the
percentages of carbon of alkanes and
alkenes.

8. Equation:
Combustion of Ethanol
C2H5OH + 3O2 → 2CO2 + 3H2O
Combustion of Propanol
C3H7OH + 9/2 O2 → 3CO2 + 4H2O
DEHYDRATION OF ALCOHOL
1.When alcohol is heated, it will decompose
to form alkene and water.
2.For example, heating ethanol will produce
ethene, heating propanol will produce
propene, and so on.
3.This process is called dehydration of
alcohol.
Dehydration of Ethanol
C2H5OH → C2H4 + H2O

9. Dehydration of Propanol
C3H7OH → C3H6 + H2O
Dehydration of Alcohols Using Aluminium
Oxide as Catalyst
Catalyst:
Aluminium oxide/ Porcelain chips

10. Dehydration of alcohols using an acid as
catalyst
Catalyst:
Sulphuric acid or Phosphoric acid
Temperature: 170°C

11. OXIDATION OF ALCOHOLS
Alcohols can be oxidised to produce
carboxylic acidwhen react with oxidising
agents.
Equation:
C2H5OH + 2[O] → CH3COOH + H2O

12. Notes:
1.The oxidising agent used:
a. Acidified potassium dichromate(VI)
b. Acidified potassium manganate (VII)
2.Observation:
a.For acidified potassium dichromate(VI), if
oxidation occurs, the orangesolution
containing the dichromate(VI) ions is
reduced to a green solutioncontaining
chromium(III) ions.
b.For acidified potassium manganate (VII),
the purple colourof potassium manganate
(VII) decolourised.
3.The alcohol is heated under reflux with
excess oxidising agent.
4.The reflux technique used to prevent the
alcohol vapour escape to the surrounding.

13. 5.When the reaction is complete, the
carboxylic acid is distilled off.
** REACTING ALCOHOLS WITH
SODIUM
Revision:
Reaction of Water with Sodium
2Na + 2H2O → 2NaOH + H2
1.We have learned the reaction of group 1
metals with cold water in Form 4 chapter
4, Periodic Table.
2.The reaction of alcohol with sodium is
similar to this reaction.
3.If a small piece of sodium is dropped into
some ethanol, it reacts steadily to give off
bubbles of hydrogen gas and leaves a
colourless solution of sodium ethoxide,

14. CH3CH2ONa.
Sodium ethoxide is known as an alkoxide.
4.In the reaction, sodium reacts with the -
OH group of alcohol, produces sodium
alkoxide and hydrogen gas.
Example:
Methanol and Sodium
2CH3OH + 2Na → 2CH3ONa + H2
Ethanol and Sodium
2C2H5OH + 2Na → 2C2H5ONa + H2