The key difference between sodium citrate and citric acid is that sodium citrate contains sodium as the cation, whereas citric acid contains hydrogen as the cation.
In fact, the sodium citrate is derived from citric acid and in that process, the hydrogen cations in the citric acid molecule are replaced by the sodium cations.
CONTENTS
1. Overview and Key Difference
2. What is Sodium Citrate
3. What is Citric Acid
4. Side by Side Comparison – Sodium Citrate vs Citric Acid in Tabular Form
5. Summary
What is Sodium Citrate?
Sodium citrate is an inorganic compound having sodium cations and citrate anions in different ratios. There are three major types of sodium citrate molecules as the monosodium citrate, disodium citrate and the trisodium citrate molecule. Collectively, these three salts are known by the E number 331. However, the most common form is trisodium citrate salt.
Figure 01: Chemical Structure of Sodium Citrate
Trisodium citrate has the chemical formula Na3C6H5O7. Most of the times, this compound is called commonly as sodium citrate because it is the most abundant form of sodium citrate salt. This substance has saline like mildly tart flavour. Furthermore, this compound is mildly basic, and we can use it to make buffer solutions along with citric acid. This substance appears as a white crystalline powder. Chiefly, sodium citrate is used in the food industry as a food additive. The purpose of using this compound is to get the flavour or as a preservative.
What is Citric Acid?
Citric acid is a weak organic acid we can find naturally in citrus fruits. There are many uses of this compound, so manufacturers tend to produce a high amount of citric acid per year. Some important uses include use as an acidifier, as a flavouring and chelating agent. There are two major forms of this compound 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 it 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.
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 the water of crystallization. This form of citric acid is formed via the crystallization from cold water.
What is the Difference Between Sodium Citrate and Citric Acid?
Sodium citrate originates from citric acid. However, the key difference between sodium citrate and citric acid is that sodium citrate contains sodium as the cation, whereas citric acid contains hydrogen as the cation. In addition to this, sodium citrate appears as a white crystalline powder while citric acid is a colourless liquid at room temperature. Moreover, sodium citrate is mildly basic while citric acid is acidic. Nevertheless, both these compounds are important as food flavouring agents and as preservatives.
The following infographic lists more differences between sodium citrate and citric acid in tabular form.
Summary – Sodium Citrate vs Citric Acid
Both sodium citrate and citric acid contain an organic chemical moiety. Sodium citrate originates from citric acid. The key difference between sodium citrate and citric acid is that sodium citrate contains sodium as the cation, whereas citric acid contains hydrogen as the cation.
Reference:
1. “Sodium Citrate.” Pubchem, Available here.
Image Courtesy:
1. “By Nossy123 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “1537823” (CC0) via Pxhere