Sunday, December 25, 2011

10th Chapter Carbon and its compounds Topic : Ethanic Acids properties ,Esterification

ETHANOIC ACID (acetic acid or vinegar, CH3COOH)
Physical properties. 
  1. It is a colourless and pungent smelling liquid.
  2. Its melting point is 290K so it often freezes during winter and looks like glacier. Therefore, it is also known as glacial acetic acid.
  3. It is soluble in water in all proportions.
    5% to 8% solution of Ethanoic acid in water is called vinegar.
Chemical properties 
  1. Reaction with alcohol. Ethanoic acid reacts with ethanol in the presence of an acid to give ester.
CH2COOH + C2H5OH --Acid---------> CH3COOC2H5 + H2O
  1. Reaction with base. Ethanoic acid reacts with sodium hydroxide to give sodium ethanoate (sodium acetate) and water.
CH3COOH + NaOH --------> CH3OONa + H2O
  1. Reaction with carbonates and bicarbonates. Ethanoic acid reacts with carbonates and bicarbonates to salt carbon dioxide and water.
2CH3COOH + Na2CO3 ------------>  2CH3COONa + CO2 + H2O
CH3COOH + NaHCO3   ----------->  CH3COONa + CO2 + H2O
Esterification The reaction between a carboxylic acid and an alcohol to form an ester is called Esterification reaction.
CH2COOH + C2H5OH ---Acid------->  CH3COOC2H5 + H2O
Q. How can ethanol and ethanoic acid be differentiated on the basis of physical and chemical properties? (V.Imp.)
Ans. Physical properties :
1. Ethanol has a sharp spirit like smell whereas ethanoic acid has a sour vinegar like smell.
2. Ethanol has a sharp bitter burning taste, whereas ethanoic acid has a sour taste.
3. On cooling ethanol does not freeze, but ethanoic acid freezes.
Chemical Properties :
1. Ethanol gets dehydrated by conc. sulphuric acid, but ethanoic acid does not get dehydrated by conc. sulphuric acid.
2. Ethanol does not displace hydrogen with zinc or magnesium, but ethanoic acid displaces hydrogen with zinc or magnesium. 
  • The reaction between the ester and hot base to give original alcohol and carboxylic acid back is called saponification reaction because this reaction is used in preparing soaps.
CH3COOC2H5 NaOH -------->   CH2COOH + C2H5OH 
The product formed when a carboxylic acid reacts with an alcohol having the formula R-COO-R’ is called an ester. 
Esters are sweet smelling substances. They are widely spread in nature. The smell of fruits and flowers is due to the presence of esters. Esters are used as flavorings agents and in making perfumes.

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