Acetic acid is an organic chemical compound with the formula CH3COOH. It is a carboxylic acid consisting of one methyl group and an attached carboxyl functional group. The systematic IUPAC name of acetic acid is ethanoic acid and its chemical formula can also be written as C2H4O2.
Vinegar is a solution of acetic acid in water and contains between 5% to 20% ethanoic acid by volume. From the smell and taste of vinegar, it can be understood that the pungent smell and the sour taste is characteristic of the acetic acid present in it.
An undiluted solution of acetic acid is commonly referred to as glacial acetic acid. It forms crystals which appear like ice at temperatures below 16.6oC. It can be used as a protic solvent with a polar nature. In the field of analytical chemistry, glacial acetic acid is widely used in order to estimate substances that are weakly alkaline.
Structure of Acetic Acid
- It can be observed in the solid state of acetic acid that there is a chain of molecules wherein individual molecules are connected to each other via hydrogen bonds.
- Dimers of ethanoic acid in its vapor phase can be found at temperatures approximating to 120o
- Even in the liquid phase of ethanoic acid, its dimers can be found when it is present in a dilute solution. These dimers are adversely affected by solvents that promote hydrogen bonding.
- The structure of acetic acid is given by CH3(C=O)OH, or CH3CO2
The structure of acetic acid is illustrated below.
Structurally, ethanoic acid is the second simplest carboxylic acid (the simplest being formic acid, HCOOH), and is essentially a methyl group with a carboxyl functional group attached to it.
Properties of Acetic Acid
Even though ethanoic acid is considered to be a weak acid, in its concentrated form, it possesses strong corrosive powers and can even attack the human skin if exposed to it. Some general properties of acetic acid are listed below.
- Ethanoic acid appears to be a colorless liquid and has a pungent smell.
- At STP, the melting and boiling points of ethanoic acid are 289K and 391K respectively.
- The molar mass of acetic acid is 60.052 g/mol and its density in the liquid form is 1.049 g.cm-3.
- The carboxyl functional group in ethanoic acid can cause ionization of the compound, given by the reaction: CH3COOH ⇌ CH3COO– + H+
- The release of the proton, described by the equilibrium reaction above, is the root cause of the acidic quality of acetic acid.
- The acid dissociation constant (pKa) of ethanoic acid in a solution of water is 4.76.
- The conjugate base of acetic acid is acetate, given by CH3COO–.
- The pH of an ethanoic acid solution of 1.0M concentration is 2.4, which implies that it does not dissociate completely.
- In its liquid form, acetic acid is a polar, protic solvent, with a dielectric constant of 6.2.
The metabolism of carbohydrates and fats in many animals is centered around the binding of acetic acid to coenzyme A. Generally, this compound is produced via the reaction between methanol and carbon monoxide (carbonylation of methanol).
Uses of Acetic Acid
Ethanoic acid is a very important organic compound in the day to day lives of humans. Some of the important uses of acetic acid are listed below.
- Acetic acid is used as an antiseptic due to its antibacterial qualities
- The manufacture of rayon fiber involves the use of ethanoic acid.
- Medically, acetic acid has been employed to treat cancer by its direct injection into the tumor.
- Being the major constituent of vinegar, it finds use in the pickling of many vegetables
- The manufacture of rubber involves the use of ethanoic acid. It is also used in the manufacture of various perfumes.
- It is widely used in the production of VAM (vinyl acetate monomer)
- When two molecules of acetic acid undergo a condensation reaction together, the product formed is acetic anhydride.
Thus, the general properties, uses, and structure of acetic acid are discussed briefly in this article. To learn more about acetic acid and the properties of the carboxyl group found in carboxylic acids, register with BYJU’S and download the mobile application on your smartphone.