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Ethyl Alcohol

Preparation of Ethyl Alcohol
By Fermentation of Sugar Present on Molasses Method
Molasses is the mother liquor left after the crystallisation of sugar in sugar industry. It is a good source of ethyl alcohol. Molasses are suitably diluted and a ferment, called yeast is mixed with it. Yeast contains two enzymes, invertase and zymase. The former breaks up the sugar molecule into glucose and fructose which has a common formula, C6H12O6. This further decomposes into C2H5OH and CO2. Good deal of frothing is caused due to liberation of CO2.



The above process is called fermentation (slow decomposition of organic compounds like the souring of milk, preparation of wine from cane sugar etc. are all fermentation processes). The fermented liquid is distilled and C2H5OH is separated. CO2 is a by-product which is used in industry. The liquid left undistilled is called the spent wash and is used as a fertiliser or feed for pigs.

By the Hydration of Ethene Method
Ethanol can be prepared by the hydration of ethene with water in the presence of H2SO4, which is a dehydrating agent.



Physical Properties of Ethanol
  1. Ethanol is a colourless gas.
  2. It mixes with water in any proportion. Due to the presence of hydroxyl group it is soluble in water.
  3. It is a neutral compound and has no effect on litmus paper.
Chemical Properties of Ethanol.


When burnt in air forms carbon dioxide and water vapour.


A lot of heat is produced during the combustion (burning) of ethanol.

In fact, all the alcohols burn in air to form carbon dioxide and water.

Oxidation means controlled combustion. Ethanol can be oxidised in two stages, first to ethanal, and then to ethanoic acid. The product formed depends on the strength of the oxidising agent used. Mild oxidising agents oxidise ethanol to ethanal (acetaldehyde) whereas strong oxidising agents oxidise ethanol to ethanoic acid (acetic acid). A mild oxidising agent for the oxidation of alcohols is chromic anhydride (CrO3) dissolved in glacial ethanoic acid (chromic anhydride is the anhydride of chromic acid, H2CrO4 and glacial ethanoic acid is the pure ethanoic acid). A strong oxidising agent for the oxidation of alcohols is alkaline potassium permanganate solution. We will now describe the two types of oxidation of ethanol.
  1. Mild Oxidation (Partial Oxidation) of Ethanol
    Take a 5 per cent solution of chromic anhydride (in glacial acetic acid) in a test tube. Add ethanol drop wise till the red colour of chromic anhydride no longer disappears. What happens? A peculiar smell due to the formation of ethanal is produced. Ethanal (Acetaldehyde) is formed by the partial oxidation of ethanol by using a mild oxidising agent. When ethanol is treated with chromic anhydride (in glacial ethanoic acid), then its partial oxidation takes place and ethanoic acid is formed:
  2. Strong Oxidation (Complete Oxidation) of Ethanol
    Take a 5 percent aqueous solution of potassium permanganate in sodium hydroxide solution in a test tube. Add ethanol dropwise till the purple colour of potassium permanganate solution no longer disappears.Warm the test tube containing ethanol and alkaline potassium permanganate solution gently in hot water bath. Ethanol is oxidised to ethanoic acid. Thus, ethanoic acid is formed by the complete oxidation of ethanol by using a strong oxidising agent. This ethanoic acid (or acetic acid) formed by the formation of ethanol can turn blue litmus to red.
    When ethanol is heated with alkaline potassium permanganate solution (which is an aqueous solution of potassium permanganate containing sodium hydroxide), its complete oxidation takes place and ethanoic acid is formed
    When ethanol is oxidised with a strong oxidising agent (like alkaline potassium permanganate), even then, ethanol is formed first. But as soon as ethanol is formed, it gets oxidised further to form ethanoic acid.

Catalytic oxidation. If ethanol vapours with air are passed over heated platinum as catalyst at 250oC, it is oxidised to acetic acid.


If ethanol vapours are passed over hot reduced copper at 300oC it is dehydrogenated (oxidised) to acetaldehyde.
Reaction with Sodium Metal
Add a small piece of sodium metal into ethanol in a dry test-tube. What do you observe? A rapid effervescence is observed due to the evolution of hydrogen gas produced in it. Bring a burning splinter near the mouth of the test-tube. The gas burns with a ‘pop’ sound. This shows that the gas produced by the action of sodium metal on ethanol is hydrogen.
In fact, all the alcohols react with sodium metal to evolve hydrogen gas. For example, methanol (CH3OH) reacts with sodium metal to form sodium methoxide (CH3ONa) and hydrogen gas.
Ethanol Reacts with Sodium to form Sodium Ethoxide and Hydrogen gas

This reaction is used as a test for ethanol.


Reaction with Ethanoic Acid (Formation of Ester)
Activity: Take some ethanol in a dry test-tube. Add an equal volume of glacial ethanoic acid (glacial acetic acid). Then add a few drops of concentrated sulphuric acid and warm the test-tube in a hot water bath. A sweet smell due to the formation of ethyl ethanoate ester is obtained.

Ethanol reacts with ethanoic acid on warming in the presence of a few drops of concentrated sulphuric acid to form a sweet smelling ester ethyl ethanoate:



The reaction in which a carboxylic acid combines with an alcohol to form an ester is called esterification. Esterification takes place in the presence of a dehydrating agent like concentrated sulphuric acid. The above reaction is an example of esterification. The formation of sweet smelling esters is used as a test for alcohols as well as carboxylic acids.
Harmful Effects of Drinking Alcohol
Ethyl alcohol is used as beverage i.e. as an intoxicant. If a person drinks it regularly, he/she will be addicted to it, losing control over his thinking process. It may even effect the heart.
It is important to note that methanol is poisonous and it should never be used for drinking purposes. It effects the eyesight badly.
Uses of Ethanol
Ethyl alcohol is a mild antiseptic and is used for cleaning wounds. It is used for sterilising injection needles, etc. and also for sterilising wounds. A mixture of alcohol and water has a much lower freezing point than water. Thus a mixture of water and ethyl alcohol, known as antifreeze, is used in radiators of vehicles in cold countries. Alcohols are also used as fuels and solvents in industries. Ethyl alcohol serves as a raw material for various chemicals.

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