Oxalic acid is an organic compound found in many plants. These include leafy greens, vegetables, fruits, cocoa, nuts and seeds. In plants, it's usually bound to minerals, forming oxalate. The terms “oxalic acid” and “oxalate” are used interchangeably in nutrition science. Its acid strength is much greater than that of acetic acid. Oxalic acid is a reducing agent and its conjugate base, is a chelating agent for metal cations.