ALCOHOLS

ALCOHOLS• Alcohols are a homologous series of organic compounds which have the

hydroxyl (-OH) functional group

• They have the general formula CnH2n+1OH

ALCOHOLSName Molecular formula Structural formula Full structural

formula

methanol CH3OH CH3OH

ethanol C2H5OH CH3CH2OH

propanol C3H7OH CH3CH2CH2OH

butanol C4H9OH CH3CH2CH2CH2OH

PHYSICAL PROPERTIES OF ALCOHOLS

Alcohol Physical state Solubility in water Boiling point /0Cmethanol liquid very soluble 65ethanol liquid very soluble 78propanol liquid very soluble 97butanol 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.

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)

CHEMICAL PROPERTIES OF ALCOHOLS• Oxidation

• alcohol + oxygen from oxidising agent + heat carboxylic acid + water

• ethanol + oxygen from oxidising agent + heat ethanoic acid + water

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

2+ + H2O

PRODUCING ETHANOL• Producing Ethanol from Ethene

• ethene + steam ethanol• 3000C• 60 atm• phosphoric (V) acid

PRODUCING ETHANOL

• CH2=CH2(g) + H2O(g) CH3CH2OH(aq)• 3000C• 60 atm• H3PO4

PRODUCING ETHANOL

+ H2O

3000C60 atmH3PO4

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.

PRODUCING ETHANOL BY FERMENTATION

• glucose solution + yeast ethanol + carbon dioxide

• C6H12O6(aq) + yeast 2C2H5OH(aq) + 2CO2(g)

WHAT ARE THE STEPS TAKEN DURING FERMENTATION?Precaution to note ReasonThe 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

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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