ETHANOIC ACID (CH3COOH)
Ethanoic acid or acetic acid is one of the most important members of the carboxylic acid family. Its molecular formula is C2H4O2. Its structural formula is
Ethanoic acid is prepared in large scale, by the oxidation of ethanol in the presence of alkaline potassium permanganate or acidified potassium dichromate.
i. Ethanoic acid is a colourless liquid having an unpleasant odour.
ii. It is sour in taste.
iii. It is miscible with water in all proportions.
iv. Its boiling point is higher than the corresponding alcohols, aldehydes and ketones.
v. On cooling, pure ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it is called glacial acetic acid.
(i) Reaction with metal: Ethanoic acid reacts with active metals like Na, Zn, etc., to liberate hydrogen and form sodium ethanoate.
2CH3COOH + Zn → (CH3COO)2 Zn + H2 ↑
2CH3COOH + 2Na → 2CH3COONa + H2 ↑
(ii) Reaction with carbonates and bicarbonates: Ethanoic acid reacts with sodium carbonate and sodium bicarbonate, which are weaker bases and liberates CO2, with brisk effervescence.
2CH3COOH + Na2CO3 → 2CH3COONa + CO2↑ + H2O
CH3COOH + NaHCO3 → CH3COONa + CO2↑ + H2O
(iii) Reaction with base: Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.
CH3COOH + NaOH → CH3COONa + H2O
(iv) Decarboxylation (Removal of CO2): When a sodium salt of ethanoic acid is heated with soda lime (solid mixure of 3 parts of NaOH and 1 part of CaO), methane gas is formed.
CH3COONa→ NaOH / CaO →CH4 ↑ + Na2CO3
Acetic acid, in lower concentration, is used as a food additive, a flavoring agent and a preservative.
Ethanoic acid is used
� in the manufacture of plastic.
� in making dyes, pigments and paint.
� in printing on fabrics.
� as a laboratory reagent.
� for coagulating rubber from latex.
� in the production of pharmaceuticals.