Acetic Acid (Vinegar) (CH₃COOH) — Properties, Uses & Safety

Overview

Acetic acid (CH3COOH), also known as ethanoic acid, is the simplest carboxylic acid after formic acid and is the compound that gives vinegar its sour taste and pungent smell. With a molar mass of 60.05 g/mol, acetic acid is a colorless liquid that is miscible with water. Household vinegar is typically a 4-8% aqueous solution of acetic acid. Pure acetic acid is called glacial acetic acid because it freezes at 16.6 °C into ice-like crystals. As a weak acid, acetic acid only partially dissociates in water (CH3COOH ⇌ CH3COO⁻ + H⁺), with a Ka of 1.8 × 10⁻⁵, making it one of the most important examples for teaching acid-base equilibrium and buffer chemistry. The acetate ion (CH3COO⁻) and acetic acid together form the classic acetic acid/acetate buffer system used in countless laboratory and biological applications. Acetic acid is found naturally in vinegar, which is produced by the bacterial oxidation of ethanol — a process known since ancient times. Industrially, most acetic acid is produced by the carbonylation of methanol (Monsanto and Cativa processes). It is one of the most important industrial chemicals, with global production exceeding 16 million tons per year. Common uses include food preservation and flavoring (as vinegar), production of vinyl acetate monomer for paints and adhesives, manufacture of acetic anhydride for pharmaceuticals, cellulose acetate for photographic film and textiles, and as a solvent and chemical reagent. In the home, vinegar is used as a natural cleaning agent and descaler. Safety-wise, concentrated acetic acid is corrosive and can cause burns to skin and eyes. GHS pictograms include the corrosion and flame symbols. For chemistry students, acetic acid is invaluable for learning about weak acid equilibria, pH calculations, buffer solutions, carboxylic acid functional groups, and esterification reactions (reacting with alcohols to form esters). The classic baking soda and vinegar volcano (NaHCO3 + CH3COOH → CH3COONa + H2O + CO2) is often a student's first hands-on chemistry experiment, making acetic acid one of the most memorable compounds in introductory chemistry.

IUPAC Name

acetic acid

CAS Number

64-19-7

PubChem CID

176

Molecular Formula

CH₃COOH

Molar Mass

60.05 g/mol

State at STP

liquid

Appearance

Colorless liquid with sharp vinegar odor

Physical Properties

Melting Point

16.6 °C

Boiling Point

117.9 °C

Density

1.049 g/cm³

ΔH°f

-484.5 kJ/mol

ΔG°f

-389.9 kJ/mol

Composition