This is a summary of the topic "Alcohols" in the GCE O levels subject: Chemistry. Students taking either the combined science (chemistry/physics) or pure chemistry will find this useful. These slides are prepared according to the learning outcomes required by the examinations board.

2. ALCOHOLS
• Alcohols are a homologous series of organic compounds which have the hydroxyl (-OH)
functional group
• They have the general formula CnH2n+1OH

3. ALCOHOLS
Name Molecular formula Structural formula Full structural formula
methanol CH3OH CH3OH
ethanol C2H5OH CH3CH2OH
propanol C3H7OH CH3CH2CH2OH
butanol C4H9OH CH3CH2CH2CH2OH

4. PHYSICAL PROPERTIES OF ALCOHOLS
Alcohol Physical state Solubility in water Boiling point /0C
methanol liquid very soluble 65
ethanol liquid very soluble 78
propanol liquid very soluble 97
butanol liquid very soluble 118
• Solubility decreases as the molecular size increases
• Boiling point increases as the molecular size increases. This is because as the sizes of alcohol molecules
increase, the forces of attraction between the molecules also increase.

5. CHEMICAL PROPERTIES OF ALCOHOLS
• Combustion
• alcohol + oxygen  carbon dioxide + water vapour
• ethanol + oxygen  carbon dioxide + water vapour
• C2H5OH(aq) + 3O2(g)  2CO2(g) + 3H2O(g)

6. CHEMICAL PROPERTIES OF ALCOHOLS
• Oxidation
• alcohol + oxygen from oxidising agent + heat  carboxylic acid + water
• ethanol + oxygen from oxidising agent + heat  ethanoic acid + water

7. CHEMICAL PROPERTIES OF ALCOHOLS
• CH3CH2OH(aq) + 2[O] + heat  CH3COOH(aq) + H2O(l)
2+  + H2O

8. PRODUCING ETHANOL
• Producing Ethanol from Ethene
• ethene + steam  ethanol
• 3000C
• 60 atm
• phosphoric (V) acid

9. PRODUCING ETHANOL
• CH2=CH2(g) + H2O(g)  CH3CH2OH(aq)
• 3000C
• 60 atm
• H3PO4

10. PRODUCING ETHANOL
+ H2O 
3000C
60 atm
H3PO4

11. PRODUCING ETHANOL BY FERMENTATION
• Alcohol fermentation is a process in which micro-organisms such as yeast act on
carbohydrates like glucose in the absence of oxygen to produce ethanol and carbon dioxide.

12. PRODUCING ETHANOL BY FERMENTATION
• glucose solution + yeast  ethanol + carbon dioxide
• C6H12O6(aq) + yeast  2C2H5OH(aq) + 2CO2(g)

13. WHAT ARE THE STEPS TAKEN DURING
FERMENTATION?
Precaution to note Reason
The temperature of the mixture should be kept at around
370C.
The enzymes in yeast work best at around 370C. If the
temperature is raised beyond 370C,the enzymes will be
denatured and therefore be unable to catalyse the
reaction. Fermentation will stop.
Fermentation can only take place in the absence of
oxygen. Hence, the apparatus needs to be air-tight. This
is ensured by the following precaution:
• The rubber bung is secured tightly to the flask.
• The limewater in the test tube prevents air from
entering the apparatus.
Fermentation can only take place in the absence of air.
This is because in the presence of air, bacteria from the
air oxidises ethanol to ethanoic acid.
ethanol + oxygen from air + bacteria  ethanoic acid +
water
CH3CH2OH(aq) + O2(g) + bacteria  CH3COOH(aq) + H2O(l)
Alcohol drinks turn sour if left exposed to air for days

14. USES OF ETHANOL
• Ethanol is used in alcoholic drinks.
• Ethanol is used as a solvent.
• Ethanol is used as a fuel.

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