The key difference between anhydrous and monohydrate citric acid is that the anhydrous citric acid has no water of crystallization whereas the monohydrate citric acid has a water molecule associated with one citric acid molecule.
Citric acid is a weak organic acid, thus, we can find it naturally in the citrus fruits. Manufacturers produce a high amount of citric acid per year because it has many uses; as an acidifier, as a flavouring and chelating agent. This compound can exist as either the anhydrous form (free of water) or as the monohydrate form.
CONTENTS
1. Overview and Key Difference
2. What is Anhydrous Citric Acid
3. What is Monohydrate Citric Acid
4. Side by Side Comparison – Anhydrous vs Monohydrate Citric Acid in Tabular Form
5. Summary
What is Anhydrous Citric Acid?
Anhydrous citric acid is the water-free form of citric acid. The appearance of this compound is colorless, and it is odorless. It has no water in its dry, granulated form. We can produce this compound via crystallization from hot water.
Figure 01: Citric Acid occurs Naturally in Lemon and Other Citrus Fruits
The anhydrous citric acid forms from the monohydrate form at 78 °C. The density of the anhydrous form is 1.665 g/cm3. It melts at 156 °C, and the boiling point of this compound is 310 °C. The chemical formula of this compound is C6H8O7 while the molar mass is 192.12 g/mol.
What is Monohydrate Citric Acid?
Monohydrate citric acid is the water-containing form of citric acid. It has one water molecule associated with one citric acid molecule. We call this water as water of crystallisation. This form of citric acid forms via the crystallization from cold water.
The monohydrate form converts into the anhydrous form at 78 °C. The density of this compound is 1.542 g/cm3. The chemical formula of this compound is C6H8O7.H2O, and the molar mass is 210.138 g/mol. The melting point is 135 °C, and the boiling point is 310 °C.
What is the Difference Between Anhydrous and Monohydrate Citric Acid?
Anhydrous citric acid is the water-free form of citric acid but, the monohydrate citric acid is the water-containing form of citric acid. This is the main difference between anhydrous and monohydrate citric acid. Furthermore, the chemical formula of anhydrous citric acid is C6H8O7. The molar mass of this compound is 192.12 g/mol. We can produce this compound via crystallization from hot water. On the other hand, the chemical formula of monohydrate citric acid is C6H8O7.H2O, and the molar mass is 210.138 g/mol. In addition, we can produce this compound via crystallization from cold water.
Summary – Anhydrous vs Monohydrate Citric Acid
Citric acid exists in two forms as anhydrous form and monohydrated form. The difference between anhydrous and monohydrate citric acid is that the anhydrous citric acid has no water of crystallization whereas the monohydrate citric acid has a water molecule associated with one citric acid molecule.
Reference:
1. Terry, Jennifer. “What Is Anhydrous Citric Acid?” LIVESTRONG.COM, Leaf Group, 3 Oct. 2017. Available here
2. “Citric Acid Monohydrate.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine. Available here
Image Courtesy:
1.’Lemon-edit1’By André Karwath aka Aka – Own work, (CC BY-SA 2.5) via Commons Wikimedia