Phosphoric acid (H₃PO₄) is an inorganic mineral acid used across food and beverage production, agriculture, industrial manufacturing, and electronics. Also known as orthophosphoric acid, it carries the food additive designation E338 and is supplied commercially as an 85% aqueous solution, a colorless, viscous, syrupy liquid. Its primary commercial roles include serving as a feedstock for phosphate fertilizers, an acidulant in cola beverages, and a metal treatment agent in industrial cleaning and coating processes.

What makes phosphoric acid valuable across such different sectors is the combination of moderate, controllable acidity with high water solubility and a non-volatile, non-flammable profile. Unlike stronger mineral acids such as hydrochloric or sulfuric acid, phosphoric acid can be handled with standard corrosive-acid precautions rather than extreme containment measures, while still providing the reactivity needed for metal treatment, pH adjustment, and fertilizer synthesis.

Phosphoric acid is classified as a corrosive substance under GHS with established hazard statements for skin, eye, and metal corrosivity. It ships under UN1805 as a Class 8 corrosive material, and its grades range from technical-purity solutions used in fertilizer and metal finishing to ACS reagent and food-grade formulations suitable for laboratory analysis and food production, respectively.

• Compound Name: Orthophosphoric acid

• Synonyms/Common Names: Phosphoric acid, orthophosphoric acid, E338

• Chemical Formula: H₃PO₄

• CAS Number: 7664-38-2

• Molar Mass: 97.994 g/mol

• Appearance: Colorless solid in anhydrous form; odorless. Commercially supplied as an 85% aqueous solution, a colorless, viscous, syrupy liquid.

Phosphoric acid is denser than water at every commercially relevant concentration, with the 85% aqueous solution measuring 1.6845 g/cm³ at 25°C and the solid anhydrous form reaching 1.834 g/cm³. This density difference matters for mixing and dilution calculations, since adding water to concentrated phosphoric acid produces a measurable volume and heat change rather than a simple linear dilution. Handlers working with high-concentration solutions should account for this when sizing containers or calculating dosing volumes.

Phosphoric acid is a colorless, odorless mineral acid widely used in industrial, food, agricultural, and laboratory applications. It functions as an acidifying agent, pH adjuster, and chemical intermediate in fertilizers, food and beverages, metal treatment, and cleaning products. U.S. laboratories and manufacturers sourcing phosphoric acid by grade and purity contact Lab Alley at 512-668-9918 for product selection and ordering support.

Anhydrous phosphoric acid melts at 42.35°C (108.23°F), while aqueous solutions boil at 100°C (212°F) as only the water component evaporates, leaving the acid behind. Heating the pure acid beyond approximately 158°C drives a dehydration reaction that converts it to pyrophosphoric acid rather than producing a true boiling transition. This means concentration through heating has a practical ceiling, beyond which the chemical identity of the product changes.

Phosphoric acid is infinitely soluble in both water and alcohol, dissolving with a small release of heat. It does not dissolve appreciably in most non-polar organic solvents, which limits its utility as a reagent in non-aqueous reaction systems. This solubility profile is part of why nearly all commercial and laboratory phosphoric acid products are formulated as aqueous solutions rather than offered as pure solute for solvent-based work.

A 0.1 N aqueous solution of phosphoric acid has a pH of approximately 1.5, reflecting its identity as a moderately strong triprotic acid with pKa values of 2.15, 7.09, and 12.32. The three dissociation steps mean phosphoric acid can buffer across a wide pH range depending on which protons have been removed, which is part of why it sees use in buffer systems and pH-control applications. Procurement and lab teams selecting concentration grades should match the intended pH target to the appropriate dissociation stage rather than assuming a single fixed acidity value.

Phosphoric acid is corrosive to most common metals and to biological tissue, and it reacts exothermically with bases in neutralization reactions. Contact with active metals such as aluminum and iron can release flammable hydrogen gas, and the acid is capable of initiating polymerization in certain organic compounds. It reacts with cyanide compounds to liberate toxic hydrogen cyanide gas, and mixtures with nitromethane are explosive, though the acid itself is non-flammable and chemically stable under normal storage conditions.

Phosphoric acid from Lab Alley is available as a high-purity, clear, colorless liquid meeting food-grade, ACS, and reagent-grade specifications for laboratory, industrial, and manufacturing applications. Packaging ranges from small laboratory containers to bulk drums and totes to support research, production, and commercial supply needs.