Acid Phosphoric Acid

Acid phosphoric acid is an inorganic compound with the chemical formula H₃PO₃, a molecular weight of 82.00, and a CAS registry number of 13598-36-2. It appears as colorless to pale yellow crystalline flakes with a garlic-like odor, and is readily soluble in water and ethanol.

Acid phosphoric acid has a density of 1.651 g/cm³, a melting point of 73℃, and a boiling point of 200℃ (decomposes). It undergoes slow oxidation in air to form orthophosphoric acid, and decomposes into orthophosphoric acid and highly toxic phosphine gas when heated to 180℃. As a dibasic acid, it is slightly more acidic than phosphoric acid and exhibits strong reducing properties: it can reduce silver ions to metallic silver and sulfuric acid to sulfur dioxide. It is highly hygroscopic, deliquescent, and corrosive.

Acid phosphoric acid is primarily used as a reducing agent and a whitening agent for nylon. It also serves as a raw material for phosphites, a pesticide intermediate, and a precursor for organophosphorus water treatment chemicals. In the plastics industry, it acts as a feedstock for manufacturing plastic stabilizers (e.g., dibasic lead phosphite), and is further utilized in the production of synthetic fibers and phosphites. Additionally, it functions as a stabilizer for polycarbonate, an antioxidant for nylon 1010, and a chemical reagent.

Acid phosphoric acid is corrosive and irritating to the skin and eyes. Protective gloves and goggles must be worn during handling. In case of accidental contact, immediately rinse the affected area with plenty of clean water and seek medical attention promptly. Classified as a Class II inorganic acidic corrosive substance with the hazard code 93014, it should be stored in a cool, well-ventilated, and dry warehouse. Storage with alkalis, flammables, and oxidizing agents is strictly prohibited.

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