Ethanoic Acid | Class X

Ethanoic acid is the second member of the homologous series of carboxylic acids (the first member being methanoic acid). The formula of ethanoic acid is CH3COOH. The common name of ethanoic acid is acetic acid. A dilute solution of ethanoic acid in water is called vinegar. Vinegar contains about 5 to 8 per cent ethanoic acid. In other words, vinegar contains about 5 to 8 per cent acetic acid. Vinegar is used widely as a preservative in pickles.

Physical properties

  • Ethanoic acid is a colourless liquid having a sour taste and a smell of vinegar
  • The boiling point of ethanoic acid is 118°C (391 K).
  • When pure ethanoic acid is cooled, it freezes to form a colourless, ice-like solid (which looks like a glacier). Due to this, pure ethanoic acid is called glacial ethanoic acid (or glacial acetic acid).
  • Ethanoic acid is miscible with water in all properties.

Chemical properties

  1. Action on Litmus: Ethanoic acid is acidic in nature. Being acidic in nature, ethanoic acid turns blue litmus red. In fact. all the carboxylic acids tum blue litmus to red. We will now compare the strength of carboxylic acids (like ethanoic acid) and mineral acids (like hydrochloric acid). Let us test both, ethanoic acid and hydrochloric acid with blue litmus paper and universal indicator paper one by one.
    • Dilute ethanoic acid turns blue litmus paper to red, showing that it is acidic in nature. Dilute hydrochloric acid also tums blue litmus paper to red, showing that it is also acidic in nature. Thus, litmus test shows that both ethanoic acid and hydrochloric acid are acidic in nature but the litmus test does not show which one is a strong acid and which one is a weak acid.
    • Dilute ethanoic acid turns universal indicator paper to orange, showing that its pH is about 4. This tells us that ethanoic acid is a weak acid. On the other hand, dilute hydrochloric acid and hydrochloric acid is a strong acid. Actually carboxylic acids (like ethanoic acid) are only partially ionized in solution (to give a small number of hydrogen ions), so they are weak acids. On the other hand, mineral acids like hydrochloric acid are completely ionized in solution (and give a large number of hydrogen ions), due to which they are strong acids.

    Due to its acidic nature, ethanoic acid reacts with carbonates, hydrogencarbonates, and bases (or alkalis) to form salts. These reactions of ethanoic acid are described below.

  2. Reaction with Carbonates and Hydrogencarbonates: Ethanoic acid reacts with carbonates and hydrogencarbonates to evolve carbon dioxide gas along with the formation a salt and water. The reactions of ethanoic acid with sodium carbonate and sodiun hydrogencarbonates are as follows:
    1. Reaction with Sodium Carbonate: Ethanoic acid reacts with sodium carbonate to form sodium ethanoate and carbon dioxide gas:
      2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
      When sodium carbonate is added to a sodium of ethanoic acid, brisk effervescence carbon dioxide is given off. The salt formed in this reaction is sodium ethanoate. The common name of sodium ethanoate is sodium acetate. All other carboxylic acids react with sodium carbonate in a similar way.
    2. Reaction with Sodium Hydrogencarbonate: Ethanoic acid reacts with sodium hydrogencarbonate to evolve brisk effervescence of carbon dioxide gas:
      CH3COOH + NaHCO3 → CH3COONa + CO2 + H2O
      This reaction is used as a test for ethanoic acid (or acetic acid). In fact, all the carboxylic acids decompose sodium hydrogencarbonate giving brisk effervescence of carbon dioxide gas.
  3. Reaction with Sodium Hydroxide: Ethanoic acid reacts with bases (or alkalis) to form salt and water. For example, ethanoic acid reacts with sodium hydroxide to form a salt called sodium ethanoate and water:
    CH3COOH + NaOH → CH3COONa + H2O
    In its reaction with bases, ethanoic acid behaves just like mineral acids (HCI, etc.). In fact all the carboxylic acids react with bases (or alkalis) like sodium hydroxide to form the corresponding salts and water.
  4. Reaction with Alcohols (Formation of Esters): Ethanoic acid reacts with alcohols in the presence of concentrated sulphuric acid to form esters. For example, when ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid. a sweet smelling ester called ethyl ethanoate is formed:
    CH3COOH + C2H5OH + Conc. H2SO4 → CH3COOC2H5 + H2

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