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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 (\(K_2Cr_2O_7\)).
The colour change occurs during this reaction where the orange colour of \(K_2Cr_2O_7\) turns to 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. This 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.
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