• This method only applies to ethanol.
• Fermentation is the chemical process which microorganism such as yeast act
on carbohydrate to produce ethanol and carbon dioxide.
• 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.
• Yeast is killed by ethanol concentrations in excess of about 15%, and that
limits the purity of the ethanol that can be produced.
PHYSICAL PROPERTIES OF ETHANOL
• Solubility in water – all members in alcohol are very soluble in water (miscible
• Volatility – all alcohols are highly volatile.
• Colour and Smell – alcohols are colourless liquid and have sharp smell.
• Boiling and melting points – all alcohols in general have low boiling points
CHEMICAL PROPERTIES OF ETHANOL
• Combustion of alcohol Complete combustion of alcohol.
C2H5OH + 3O2 –> 2CO2 + 3H2O
• Alcohol burns with clean blue flames. Alcohol burns plenty of oxygen to
produce carbon dioxide and water. This reaction releases a lot of heat.
Therefore, it is a clean fuel as it does not pollute the air.) Other example:
2C3H7OH + 9O2 –> 6CO2 + 8H2O
• Oxidation of ethanol In the laboratory, two common oxidising agents are
used for the oxidation of ethanol which are acidified potassium
dichromate(VI) solution (orange to green) and acidified potassium
manganate(VII) solution (purple to colourless). C2H5OH + 2[O] –> CH3COOH +
H2O Ethanol oxidised to ethanoic acid (a member of the homologous series of
carboxylic acids – will be discussed in Part 6). Other example:
C3H7OH + 2[O] –> C2H5COOH + H2O
• Removal of water (Dehydration) Alcohol can change to alkene by removal of
water molecules (dehydration). It results in the formation of a C=C double
CnH2n+1OH –> CnH2n + H2O C2H5OH –> C2H4 + H2O
• Two methods are being used to carry out a dehydration in the laboratory.
• a) Ethanol vapour is passed over a heated catalyst such as aluminium oxide,
unglazed porcelain chips, pumice stone or porous pot.
• b) Ethanol is heated under reflux at 180°C with excess concentrated sulphuric
acid, H2SO4. Other example:
C3H7OH –> C3H6 + H2O
USES OF ALCOHOL
• Alcohol as a solvent (cosmetics, toiletries, thinners, varnishes, perfumes).
• Alcohol as a fuel (fuel for racing car, clean fuel, alternative fuel).
• Alcohol as a source of chemicals (polymer, explosives, vinegar, fiber).
• Alcohol as a source of medical product (antiseptics for skin disinfection,
EFFECT OF MISUSE AND ABUSE OF
• Most alcohol are poisonous. Methanol very toxic. Small amounts can result in blindness.
Drinking more than 30cm of methanol can lead to death of the drinker.
• Excess drinking of alcohol can be very dangerous. If it used over a long period of time,
ethanol destroys the tissues of liver (cirrhosis).
• Ethanol is believed to destroy the brain cell slowly. This can result in a loss of memory.
• Under the influence of alcohol, the drinker may feel happy and like to socialise. However,
excessive drinking leads to drunkenness.
• a) The liver cannot break down the large amounts of ethanol absorbed all at once.
• b) The working of the nerves in our brain is affected by the higher concentration
of ethanol in the blood. Thus, alcohol can lower our thinking ability.
• c) Habitual drinking of alcohol is not healthy.
• d) Alcohol can also affect the healthy growth of the brain for children consuming the
• Pregnant woman who drink may give birth to babies with smaller birth weight or even babies
with birth defects.