Phosphoric acid, or orthophosphoric acid, is a common inorganic acid. It is a medium strong acid with a chemical formula of H3PO4 and a molecular weight of 97.994. It is not easy to volatilize, not easy to decompose, and has almost no oxidizing properties. It is a ternary weak acid with acidity. Its acidity is weaker than hydrochloric acid, sulfuric acid, nitric acid, but stronger than acetic acid, boric acid, etc. It can be obtained by dissolving phosphorus pentoxide in hot water. Orthophosphoric acid is obtained by treating apatite with sulfuric acid in the industry. Phosphoric acid is easily deliquescent in the air. Heating causes loss of water to obtain pyrophosphoric acid, and further loss of water to obtain metaphosphoric acid.