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Ethanoic acid (\(CH_3COOH\)), commonly known as acetic acid, is one of the most important compounds of the carboxylic acid circle of relatives. Its molecular formula is \(C_2H_4O_2\). The structural formula for ethanoic acid is,
Ethanoic acid
Preparation of ethanoic acid:
Ethanoic acid is prepared on a large scale through the oxidation of ethanol in the presence of alkaline potassium permanganate or acidified potassium dichromate.
Physical properties of ethanoic acid:
- Colourless liquid with a strong odour.
- Acids are sour in taste, and so is ethanoic acid.
- They are miscible in water irrespective of their proportions.
- They have a higher boiling point than the corresponding groups of aldehyde, alcohol and ketones.
- Pure ethanoic acid on cooling forms ice-like flakes. As it resembles glaciers it is known as glacial acetic acid.
Chemical properties of ethanoic acid:
a) Reaction with metal:
The reaction of active metals (such as Na, Zn, etc.) with ethanoic acid forms ethanoate with the liberation of hydrogen gas.
\(2CH_3COOH + Zn \rightarrow (CH_3COO)_2Zn + H_2\)
Zinc ethanoate
\(2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2\)
Sodium ethanoate
b) Reaction with carbonates and bicarbonates:
Ethanoic acid reacts with weaker bases such as sodium carbonate (\(Na_2CO_3\)) and sodium bicarbonate (\(NaHCO_3\)), forming its salt, water along with the liberation of brisk effervescence (\(CO_2\)).
\(2CH_3COOH + NaCO_3 \rightarrow 2CH_3COONa + CO_2 + H_2O\)
Sodium ethanoate
\(CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + CO_2 + H_2O\)
Sodium ethanoate
c) Reaction with base:
Sodium ethanoate and water is formed when ethanoic acid reacts with sodium hydroxide.
\(CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O\)
Sodium ethanoate
d) Decarboxylation (removal of \(CO_2\)):
The reaction of soda lime (solid mixture of 3 parts of \(NaOH\) and one part of \(CaO\)) with the sodium salt of ethanoic acid produces methane gas.
\(CH_3COOH \xrightarrow {NaOH /CaO} CH_4+ Na_2CO_3\)
Methane
gas
Uses of ethanoic acid:
- Lower concentrations of acetic acid (vinegar) are used as a food additive, flavouring agent, and preservative.
- They are used in the manufacturing of plastics.
- Used in making dyes, pigments and paints.
- It is used as a laboratory reagent and for printing on fabrics.
- They are also used for coagulating rubber from latex.
- Ethanoic acid is used in the production of pharmaceuticals.
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