Oxalic acid is the simplest dicarboxylic acid, also known as oxalic acid. It is a colorless and transparent crystal at room temperature, usually containing two molecules of crystal water. When heated to 100.1℃, it loses crystal water and becomes anhydrous oxalic acid. Toxic and harmful to human body. It is hygroscopic, soluble in ethanol, water and slightly soluble in ether. Insoluble in benzene and chloroform. Oxalic acid can form water-soluble complexes with many metals. Because the molecule is directly connected by two carboxyl groups, its acidity is stronger than other binary organic acids, and its acidity is 10,000 times that of acetic acid. It has strong reducibility of Chemicalbook, and is easily oxidized to carbon dioxide and water by the action of oxidant. In acidic solution, oxalic acid can be quantitatively oxidized by potassium permanganate, which reduces potassium permanganate solution to divalent manganese and fades. Oxalic acid with crystal water is an easily purified crystal, which is often used in volumetric analysis. At 189.5℃ or in case of concentrated sulfuric acid, it will decompose to generate carbon dioxide, carbon monoxide and water. In the laboratory, oxalic acid can be decomposed by heat to produce carbon monoxide gas. There is also a small amount of oxalic acid in human urine, and calcium oxalate is the main component of urethral calculi.