Oxalic acid is the chemical compound with the formula H2C2O4. This colourless solid is a dicarboxylic acid. In terms of acid strength, it is about 3,000 times stronger than acetic acid. Its conjugate base, known as oxalate (C2O42−), is a reducing agent as well as a chelating agent for metal cations. Typically oxalic acid occurs as the dihydrate with the formula C2O4H2·2H2O.