Oxalic acid is an organic acid with the IUPAC name ethanedioic acid and formula HO 2C−CO 2H. It is the simplest dicarboxylic acid. Oxalic acid has many roles as a bleach, metal polish, stain remover, and mordant. It is used as a Bleaching agent for Straw hats, Leather, and Wood. Oxalic acid acts as a reducing agent for metal oxides to remove tarnish as well as rust or ink stains