Phosphoric acid
[CAS# 7664-38-2]

Identification

• Classification: Inorganic chemical industry >> Inorganic acid
• Name: Phosphoric acid
• Synonyms: Orthophosphoric acid
• Molecular Formula: H₃PO₄
• Molecular Weight: 97.99
• CAS Registry Number: 7664-38-2
• EC Number: 231-633-2
• SMILES: OP(=O)(O)O

Properties

• Solubility: Miscible
• Density: 1.685
• Melting point: 21 °C
• Boiling point: 158 °C
• Refractive index: 1.431

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H290-H302-H314-H318
• Safety Statements: P234-P260-P264-P264+P265-P270-P280-P301+P317-P301+P330+P331-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P321-P330-P363-P390-P405-P406-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin corrosion	Skin Corr.	1B	H314
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H302
Eye irritation	Eye Irrit.	2	H319
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Skin corrosion	Skin Corr.	1C	H314
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin corrosion	Skin Corr.	1	H314
Skin corrosion	Skin Corr.	1A	H314
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	3	H331
Specific target organ toxicity - single exposure	STOT SE	1	H370

• Transport Information: UN 1805

Discovery and Applications

Phosphoric acid was first discovered in 1770 by Swedish chemist Carl Wilhelm Scheele, who obtained it by reacting phosphorus with nitric acid. Phosphoric acid is a tribasic acid containing three hydrogen atoms, one phosphorus atom, and four oxygen atoms. In its pure form, phosphoric acid is a colorless, odorless, crystalline solid, but it is often found as a viscous liquid or aqueous solution.

Phosphoric acid is the main ingredient in the production of phosphate fertilizers. It is used to produce monoammonium phosphate (MAP) and diammonium phosphate (DAP), which provide essential phosphorus and nitrogen for crops. Phosphorus is essential for plant development, helping root growth, flower formation, and energy transfer, making it indispensable in improving soil fertility and crop yields. In animal nutrition, phosphoric acid is used to fortify feed with phosphorus to promote healthy bone development and metabolic function in livestock. It ensures adequate phosphorus intake to support growth and productivity of agricultural animals.

Phosphoric acid is widely used as an acidulant in the food and beverage industry. It adds sourness and adjusts the pH of products such as soft drinks, processed foods, and jams. It is a key ingredient in many food formulations to enhance taste and stability by balancing flavors and extending shelf life. In food preservation, phosphoric acid helps control microbial growth and prolong the freshness of perishable foods. It serves as a preservative for canned foods, cheeses, and other products, ensuring long-term safety and quality.

Phosphoric acid is used in metal treatment processes, particularly rust removal. It converts iron oxide (rust) into water-soluble phosphates, which facilitate cleaning and preparation of metal surfaces for painting or coating. The process improves corrosion resistance and adhesion of the protective layer. In the production of detergents and cleaners, phosphoric acid acts as a pH adjuster and cleaning agent. Its ability to remove mineral deposits and grease makes it very effective in the formulation of household and industrial cleaning products. Phosphoric acid is an intermediate in the synthesis of various pharmaceuticals. It is used to prepare phosphate-based drugs and as an acidifier in some pharmaceutical formulations to enhance the stability and absorption rate of active ingredients. In water treatment, phosphoric acid helps control pH and prevent corrosion in water supply systems. It is also used in the formulation of preservatives to protect pipes and infrastructure from corrosion.

References

1987. Simultaneous Phenotyping of Genetic Markers for Paternity Testing. Zeitschrift fur Rechtsmedizin. Journal of legal medicine, 98(3).
DOI: 10.1007/bf00200633

1984. Pharmacokinetics of ciprofloxacin after oral and intravenous administration in healthy volunteers. European Journal of Clinical Microbiology & Infectious Diseases, 3(4).
DOI: 10.1007/bf01977494

1971. The genus Candida Berkhout. XII. Chemical composition of polysaccharides isolated from cell walls of three strains of Candida guilliermondii (Cast.) Langeron et Guerra and their immunochemical properties. Folia Microbiologica, 16(6).
DOI: 10.1007/bf02872713