Oxalic acid is a dicarboxylic acid. It is a colourless crystalline solid that dissolves in water to give colourless, acidic solutions. In terms of acid strength, it is much stronger than acetic acid. Oxalic acid, because of its di-acid structure can also act as a chelating agent for metal cations.
Oxalic acid's main applications include cleaning or bleaching, especially for the removal of rust (iron complexing agent). Its utility in rust removal agents is due to its forming a stable, water-soluble salt with ferric iron, ferrioxalate ion. Oxalic acid is an ingredient in some tooth whitening products. About 25% of produced oxalic acid will be used as a mordant in dyeing processes. It is also used in bleaches, especially for pulpwood, and for rust removal and other cleaning, in baking powder, and as a third reagent in silica analysis instruments.