Ethanoic acid

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

1. Manufacture of ethanoic acid

Ethanoic acid is prepared in large scale, by the oxidation of ethanol in the presence of alkaline potassium permanganate or acidified potassium dichromate.

2. Physical Properties

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.

3. Chemical Properties

(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

4. Uses of ethanoic acid

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.