LEARNATHON
III

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Theory:

Let us now see the physical and chemical properties of ethanol and its uses:
a) Physical properties of ethanol (\(C_2H_5OH\)):
  • It is a colourless liquid, has a pleasant smell and a burning taste.
  • It is a volatile liquid with the boiling point at \(780°C\) (\(351K\)), which is far above that of its corresponding alkane, i.e. ethane (Boiling Point = \(184 K\)).
  • It is completely miscible in water irrespective of its proportions.
  
b) Chemical properties of ethanol (\(C_2H_5OH\)):
 
1. Dehydration (Loss of water):
 
There is a loss of water molecules when ethanol reacts with concentrated sulphuric acid (\(H_2SO_4\)) at \(443K\), i.e. dehydrated to form ethene.
 
Therefore, the chemical reaction is represented as
\(CH_3CH_2OH \xrightarrow [443K]{Conc H_2SO_4} CH_2=CH_2 + H_2O\)
  Ethanol                                         Ethene               Water
 
2. Reaction with sodium:
  
The reaction of sodium metal with ethanol produces sodium ethoxide and hydrogen gas.
 
Therefore, the chemical reaction is represented as
\(2CH_3CH_2OH + 2Na \rightarrow  2C_2H_5ONa + H_2\)
Ethanol                 Sodium             Sodium          Hydrogen
                                                        ethoxide           gas
 
3. Oxidation:
  
Ethanoic acid is formed when ethanol is oxidised with alkaline potassium permanganate (\(KMnO_4\)) or acidified potassium dichromate (\(K_2Cr_2O_7\)).
 
CH3CH2OH 2[O]K2Cr2O7CH3COOH+H2OEthanolEthanoicacid
 
The colour change occurs during this reaction where the orange colour of  \(K_2Cr_2O_7\) turns green. This reaction can be used for the identification or confirmation of the alcohol group.
 
4. Esterification:
  
Alcohol in reaction with a carboxylic acid produces a compound having a fruity odour. This compound is referred to as an ester, and the reaction is known as esterification.
 
Ethanol on reaction with ethanoic acid in the presence of concentrated sulphuric acid (\(H_2SO_4\)) forms ethyl ethanoate (an ester compound).
 
 
\(CH_3CH_2OH + CH_3COOH \xrightarrow {Conc H_2SO_4} CH_3COOC_2H_5 + H_2O\)
Ethanol                  Ethanoic acid                              Ethyl ethanoate
 
 
5. Dehydrogenation:
 
The process of dehydrogenation occurs when vapours of ethanol pass over hot copper (\(Cu\)) at \(573K\). In this reaction, copper is used as a catalyst. Dehydrogenation of ethanol forms acetaldehyde (\(CH_3CHO\)).
 
\(CH_3CH_2OH  \xrightarrow [573K]{Cu} CH_3CHO  +  H_2\)
Ethanol                                Acetaldehyde   Hydrogen
                                                                         gas
 
6. Combustion:
  
Ethanol is a volatile and highly inflammable liquid. Carbon dioxide (\(CO_2\)) and water are formed when ethanol reacts with oxygen (O_2\).
 
\(CH_3CH_2OH  + 3O_2 \rightarrow 2CO_2  +  3H_2O\)
Ethanol                    Oxygen    Carbon    Water
                                                  dioxide           
 
c) Uses of ethanol:
  • It is used in medical wipes as an antiseptic.
  • It is used as an anti-freeze in automobile radiators.
  • It effectively kills microorganisms like bacteria, fungi, etc., as it is used in hand sanitisers.
  • It is used as an antiseptic to sterilise wounds in hospitals.
  • It is used as a solvent for drugs, oils, fats, perfumes, dyes, etc. 
  • It is used in the preparation of methylated spirit (mixture of \(95%\) of ethanol and \(5%\) of methanol), rectified spirit (mixture of \(95.5%\) of ethanol and \(4.5%\) of water), power alcohol (mixture of petrol and ethanol) and denatured spirit (ethanol mixed with pyridine).
  • It is used to enhance the flavour of food extracts, for example, vanilla extract.
  • It is a common food flavour made by processing vanilla beans in a solution of ethanol and water.