ALCOHOL

 

1. General formula: C_nH_{2n + 1}OH

• Where n = 1, 2, 3 … (n = number of carbon)

2.  An alcohol is an organic compound in which the 
     hydroxyl functional group (-O H) is  
     bound to a carbon atom. In particular, this carbon  
     center should be saturated, having   
    single bonds to three other atoms.


 3. The functional group in alcohols is hydroxyl group, – OH.

Name of alcohol	Molecular formula of alcohol
Methanol	CH3OH
Ethanol	C2H5OH
Propanol / Propan-1-ol	C3H7OH
Butanol / Butan-1-ol	C4H9OH
Pentanol / Pentan-1-ol	C5H11OH
Hexanol / Hexan-1-ol	C6H13OH
Heptanol / Heptan-1-ol	C7H15OH
Octanol / Octan-1-ol	C8H17OH
Nonanol / Nonan-1-ol	C9H19OH
Decanol / Decan-1-ol	C10H21OH

4. Physical properties of alcohol

Name	Molecular formula	Melting point (°C)	Boiling point (°C)	Physical state at 25°C
Methanol	CH3OH	-97	65	Liquid
Ethanol	C2H3OH	-117	78	Liquid
Propanol	C3H5OH	-127	97	Liquid
Butanol	C4H7OH	-90	118	Liquid
Pentanol	C5H9OH	-79	138	Liquid

• Solubility in water – all members in alcohol are very soluble in water (miscible with water).
• 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 (78°C).

5. Chemical properties of alcohol

• 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.)

• Oxidation of ethanol 

          Two common oxidising agents are used for the oxidation of ethanol.

          1. Acidified  potassium dichromate(VI) solution (orange to green)

          2. Acidified potassium manganate(VII) solution (purple to colourless). 
   
                   C₂H₅OH + 2[O] –> CH₃COOH + 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 bond. 
          C_nH_2n+1OH –> C_nH_2n + 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. 
                              
                                    C₃H₇OH –> C₃H₆ + H₂O 


6. Uses of Alcohol

cosmetic

• Alcohol as a solvent (cosmetics, toiletries, thinners, varnishes, perfumes).

clean fuel



vinegar

• Alcohol as a fuel (fuel for racing car, clean fuel, alternative fuel).

• Alcohol as a source of chemicals (polymer, explosives, vinegar, fiber).

Mouth wash

• Alcohol as a source of medical product (antiseptics for skin disinfection, rubbing alcohol).

Manufacture of Ethanol (Hydration)

Ethanol is manufactured by reacting ethene with steam. The reaction is reversible, and the formation of the ethanol is exothermic.

 

An experiment can be done in laboratory to obtained ethene.

Method to Obtain Ethene