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What No One Told You About the Chemical Formula of Citric Acid

Omkar Phatak Jun 18, 2019
If you are looking for the citric acid formula, this write-up has what you seek. Read to know all about it.
Why is it important that one knows the molecular formula for citric acid? Isn't knowing the name good enough? The answer to that question is in the negative, as chemistry is a science that does more than just name chemicals. A real chemical name describes the constitution of atoms that bind to make it.
Modern chemists have developed a system of naming chemicals, that not only describes the atoms and number of atoms that make that make it, but also the overall arrangement of the atoms and their relation to each other. The specific arrangement of atoms, conveyed by the molecular formula for citric acid, gives it a unique identity and properties.
At room temperature, it is a white powder, has a melting point of 153° C and a molar mass of 192.124 gm per mole. It is an important intermediate product of the process of respiration and is the key link in the citric acid cycle. It is a weak organic acid which is found in most of the citrus fruits and has myriad uses.

Chemical Formula

A citric acid molecule is a combination of carbon, hydrogen, and oxygen atoms, bonded in a unique arrangement. The molecular formula is:

Formula : C6H8O7

All this formula tells us is how many atoms of carbon, hydrogen, and oxygen are contained within this molecule.
There may be many other structures, that have the same atoms, in the same number, and yet they are not citric acid molecules. That is because, this acid receives its properties from the specific arrangement of atoms in its molecule. That is why, a chemical formula should describe the arrangement of atoms in it.
Here is the formula and structure, enumerated through its IUPAC (International Union of Pure and Applied Chemistry) name:

Citric Acid (IUPAC) Formula: 3 - Carboxy - 3 - Hydroxy Pentanedioic Acid
Understanding this formula, requires a knowledge of the IUPAC nomenclature, but here is a simple explanation. The nomenclature for organic acids is designed to accurately describe the arrangement of atoms in this molecule. Most organic compounds are made from a chain of carbon atoms, that forms its backbone.
This formula describes the structure of the molecule in the following manner.
  • Carboxy: It stands for the functional group '- COOH'
  • Hydroxy: stands for the functional group '- OH'
  • Pentanedioic: Penta prefix indicates that this compound has 5 carbon atoms and each end atom is a carboxyl group.
The full chemical formula means the following:

'Citric Acid can be pictured to be derived from Pentanedioic by the attachment of one hydroxy group and one carboxy group at the third carbon atom.'
This is just one way of describing the chain of atoms in this molecule. One could alternatively name it differently by adopting a different set of rules for naming. A common name for the acid is 'Hydrogen Citrate'. Using other nomenclatures, the it can also be named as:
  • 2-hydroxypropane- 1,2,3- tricarboxylic acid
  • 3-hydroxypentanedioic acid-3-carboxylic acid
Of course, even though names change, the molecule remains the same. A knowledge of nomenclature is necessary, if you intend to understand the names of the various chemical compounds. It is a painstaking job for a chemist to determine the structure of a molecule. It is one of the most sophisticated forms of detective work.
Finding out the structure of various complex molecules is the major part of research in organic chemistry. The knowledge of the constituent parts of a molecule, helps you understand every one of its properties.