Citric acid is a weak organic acid that is widely used in various industries, including food and beverage, pharmaceutical, and chemical industries. Its solubility in water and other solvents is an essential property that determines its applications. This comprehensive guide will provide you with detailed information on the solubility of citric acid, including its temperature-dependent solubility, solubility in other solvents, and other relevant physical and chemical properties.
Temperature-Dependent Solubility of Citric Acid in Water
The solubility of citric acid in water is highly dependent on temperature. According to the Technical Evaluation Report on Citric Acid and its Salts by the Agricultural Marketing Service, the solubility of citric acid in water is as follows:
| Temperature (°C) | Solubility (% w/w) |
|---|---|
| 10 | 54.0 |
| 20 | 59.2 |
| 30 | 64.3 |
| 40 | 68.6 |
| 50 | 70.9 |
| 60 | 73.5 |
| 70 | 76.2 |
| 80 | 78.8 |
| 90 | 81.4 |
| 100 | 84.0 |
This data shows that the solubility of citric acid in water increases significantly with increasing temperature. At 10°C, the solubility is 54.0% w/w, while at 100°C, the solubility increases to 84.0% w/w.
The temperature-dependent solubility of citric acid can be described by the following equation:
log(S) = A + B/T
where S is the solubility of citric acid in water (g/100g water), T is the absolute temperature (K), and A and B are constants. The values of A and B for citric acid are -0.4343 and 1810, respectively.
This equation can be used to calculate the solubility of citric acid at any given temperature within the range of 10°C to 100°C.
Solubility of Citric Acid in Other Solvents
In addition to its solubility in water, citric acid also exhibits solubility in other solvents. The solubility of citric acid in ethanol and ether at 25°C is as follows:
- Ethanol, 25°C: 58.9 g/100ml
- Ether, 25°C: 1.84 g/100ml
The high solubility of citric acid in ethanol makes it useful in the production of cosmetics and personal care products, where it can be used as a pH regulator or preservative.
Physical and Chemical Properties of Citric Acid
Citric acid has several other physical and chemical properties that are important to consider when working with this compound. Some of these properties are:
Density
- Citric acid monohydrate: 1.542 g/cm³
- Anhydrous citric acid: 1.665 g/cm³
Refractive Index
- Citric acid monohydrate: 1.493, 1.498, 1.509
- Anhydrous citric acid: 1.542
Heat of Combustion
- Citric acid monohydrate: -471.4 kcal/mol
- Anhydrous citric acid: -474.5 kcal/mol
Bulk Density
- Anhydrous citric acid: 56.2 lbs./cu ft
Ionization Constants
- K1 = 8.2 x 10^-4
- K2 = 1.8 x 10^-5
- K3 = 3.9 x 10^-6
pKa Values
- pKa1 = 3.13
- pKa2 = 4.76
- pKa3 = 6.39
Viscosity
- 50% aqueous solution at 25°C: 6.5 cP
Standard Free Energy of Anion Formation
- ∆F°f for aqueous solutions at 25°C: -278.8 kcal
These physical and chemical properties of citric acid are important to consider when working with this compound in various applications, such as in the food and beverage industry, pharmaceutical industry, and chemical industry.
Conclusion
In summary, this comprehensive guide has provided detailed information on the solubility of citric acid, including its temperature-dependent solubility in water, solubility in other solvents, and other relevant physical and chemical properties. This information is essential for understanding the behavior and applications of citric acid in various industries.
References
- Technical Evaluation Report on Citric Acid and its Salts, Agricultural Marketing Service: https://www.ams.usda.gov/sites/default/files/media/Citric%20Acid%20TR%202015.pdf
- Citric Acid Assay Kit, Megazyme: https://www.megazyme.com/citric-acid-assay-kit
- Solubility and Thermodynamic Properties of Citric Acid in Water-Ethanol Mixtures, Science Direct: https://www.sciencedirect.com/science/article/pii/S1021949817300558
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