The key difference between citric acid and acetic acid is that citric acid has three carboxylic acid groups, whereas acetic acid has one carboxylic acid group.
Both citric acid and acetic acid are organic carboxylic acid compounds having the carboxylic acid functional group (-COOH). However, they differ from each other according to the number of carboxylic acid groups in these molecules.
What is Citric Acid?
Citric acid is an organic compound having the chemical formula HOC(COOH). It is a colorless weak organic acid and naturally occurs in citrus fruits. In biochemical terms, citric acid is an intermediate in the citric acid cycle during the metabolism of all aerobic organisms. Typically, about 2 million tons of citric acid are manufactured annually. This substance is widely important as an acidifier and as a flavoring agent. It is also important as a chelating agent.
The molar mass of this compound is 192 g/mol in its anhydrous state. When isolated, citric acid appears as a white solid that is odorless. The density of the anhydrous form is about 1.66 g/cm3. Its melting point is 156 degrees Celsius, and its boiling point is 310 degrees Celsius. However, it starts to decompose at about 175 degrees Celsius. Moreover, citric acid is soluble in acetone, alcohol, ether, ethyl acetate, but it’s insoluble in toluene. The crystal structure of the solid citric acid is monoclinic.
Typically, this acid can be found in many different fruits and vegetables but mainly in citrus fruits. For example, lemon and lime have a very high content of citric acid. When industrially preparing this substance, it was first done by treating the juice with hydrated lime (calcium hydroxide) to get the precipitate of calcium citrate, which is then isolated and converted back to citric acid using sulfuric acid. However, in modern industries, citric acid is prepared by fungal fermentation methods.
What is Acetic Acid?
Acetic acid is an organic compound having the chemical formula CH3COOH. It is also known as ethanoic acid and occurs as an acidic, colorless liquid having a heavily vinegar-like odor. The molar mass of this compound is 60 g/mol. The density can be given as 1.05 g/cm3. The melting point ranges from 61 to 62 degrees Celsius, and the boiling point can range from 118 to 119 degrees Celsius. It is miscible with water.
We can say acetic acid is the second simplest carboxylic acid because it has one carboxylic acid functional group attached to a carbon atom. (The simplest carboxylic acid is formic acid – HCOOH, the carboxylic acid group is not attached to any carbon atom). Acetic acid is important in many different industries, such as the production of cellulose acetate, polyvinyl acetate, synthetic fibers, etc. In the food industry, this chemical is useful as a food additive with the E number E260.
The carboxylic acid functional group in an acetic acid molecule can undergo partial ionization to form acetate ion and hydrogen cation (proton). Releasing this proton causes the acidic nature of acetic acid. Therefore, we can name this chemical as a weak monoprotic acid (which means it partially dissociates and give one proton per molecule). Typically, the solid acetic acid has chains of molecules, and these molecules are interconnected by hydrogen bonding. In its vapor phase, we can detect dimers of acetic acid molecules. In its liquid state, it is a hydrophilic polar protic solvent.
What is the Difference Between Citric Acid and Acetic Acid?
Citric acid and acetic acid are important organic compounds having carboxylic acid functional groups. These two compounds are different from each other according to the number of functional groups per molecule and, thus, their chemical and physical properties. The key difference between citric acid and acetic acid is that citric acid has three carboxylic acid groups, whereas acetic acid has one carboxylic acid group.
Summary – Citric Acid vs Acetic Acid
The carboxylic acid functional group has the chemical formula –COOH. Citric acid and acetic acid contain this type of functional group in their molecules. The key difference between citric acid and acetic acid is that citric acid has three carboxylic acid groups, whereas acetic acid has one carboxylic acid group.
1. “Acetic Acid: General Information.” GOV.UK.
1. “Citrus fruits” By Scott Bauer, USDA – The research agency of the United States Department of Agriculture, with the ID K7226-29 (Public Domain) via Commons Wikimedia
2. “Acetic Acid Hydrogenbridge V.1” By Jü – Own work (Public Domain) via Commons Wikimedia