Hypophosphorous acid (also known as phosphinic acid in English) is an inorganic compound with the chemical formula H_{3}PO_{2}.

Physical and chemical properties

• Appearance: Pure hypophosphorous acid is a colorless oily liquid or deliquescent crystals. The most common is its 50% aqueous solution, which is a colorless transparent liquid.
• Melting point: The melting point of the pure product is 26.5^{\circ}C.
• Boiling point: 107.8^{\circ}C (decomposition).
• Density: The relative density (compared to water = 1) is 1.49 (for the pure product). It is easily soluble in hot water, ethanol and ether, and can also be soluble in cold water.
• Acid-base properties: It is a dibasic weak acid that partially ionizes hydrogen ions in aqueous solution.
• Chemical stability: When heated to 130^{\circ}C, it decomposes into orthophosphoric acid and phosphine (PH_{3}, highly toxic). It has strong reducing properties and can react with many oxidants.