What is the Difference Between Oxalic Acid and Citric Acid

The key difference between oxalic acid and citric acid is that oxalic acid has two carboxylic functional groups and comparatively a low chemical reactivity, whereas citric acid has three carboxylic acid groups, hence high chemical reactivity.

Oxalic acid and citric acid are types of carboxylic acid compounds because they have carboxylic acid functional groups. These acids have different numbers of carboxylic acid groups per molecule.

CONTENTS

1. Overview and Key Difference
2. What is Oxalic Acid  
3. What is Citric Acid
4. Oxalic Acid vs Citric Acid in Tabular Form
5. Summary – Oxalic Acid vs Citric Acid 

What is Oxalic Acid?

Oxalic acid is an organic acidic compound having the chemical formula H2C2O4. This compound exists as a colourless solid that can easily dissolve in water. This acidic compound is a dicarboxylic acid because it is formed from the combination of two carboxylic acid groups; in fact, it is the simplest dicarboxylic acid. Furthermore, it has a high acid strength, and we can name it as a strong reducing agent. The conjugate base of oxalic acid is an oxalate ion. Generally, oxalic acid occurs in the dihydrate form, and it naturally occurs in some food. The molar mass of the anhydrous form of this acidic compound is 90 g/mol.

Figure 1: The Chemical Structure of Oxalic Acid

We can produce oxalic acid from the oxidation of carbohydrates or glucose using nitric acid or air in the presence of vanadium pentoxide. There are two polymorphs of oxalic acid where one polymorphic structure has a chain-like structure due to the presence of hydrogen bonds while the other polymorphic structure is in the sheet-like structure.

When considering the uses of oxalic acid, it is useful in cleaning and bleaching purposes, as a reagent in extractive metallurgy, in aluminum anodizing process, etc.

What is Citric Acid?

Citric acid is a weak organic acid having the chemical formula C6H8O7. It occurs naturally in citrus fruits. There are many applications of this compound. Therefore, manufacturers tend to produce a high amount of citric acid annually. Some of the important applications include use as an acidifier, as a flavouring, and as a chelating agent. There are two forms of this acid as the anhydrous form and the monohydrated form.

The anhydrous form of citric acid is the water-free form. It appears as a colourless substance and is odourless as well. There is no water in its dry, granulated form. We can produce this compound via crystallization from hot water.

The anhydrous citric acid is formed 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.

Figure 02: The Chemical Structure of 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 the water of crystallization. This form of citric acid is formed via crystallization from cold water.

What is the Difference Between Oxalic Acid and Citric Acid?

Oxalic acid is an organic acidic compound having the chemical formula H2C2O4, while Citric acid is a weak organic acid having the chemical formula C6H8O7. The key difference between oxalic acid and citric acid is that oxalic acid has two carboxylic functional groups and comparatively a low chemical reactivity, whereas citric acid has three carboxylic acid groups, hence high chemical reactivity.

The following infographic lists the differences between oxalic acid and citric acid in tabular form for side by side comparison.

Summary – Oxalic Acid vs Citric Acid

Oxalic acid is an organic acidic compound having the chemical formula H2C2O4, whereas citric acid is a weak organic acid having the chemical formula C6H8O7. The key difference between oxalic acid and citric acid is that oxalic acid has two carboxylic functional groups and comparatively a low chemical reactivity, whereas citric acid has three carboxylic acid groups, hence high chemical reactivity.