Description General description Oxalic acid dihydrate crystals are monoclinic and exhibit a space group P21/n. Each unit cell contains two molecules. 13C chemical shielding tensors in oxalic acid dihydrate have been evaluated. Application Oxalic acid dihydrate has been used to prepare oxalate precursor, which was employed for the synthesis of zinc oxide nanopowders. It may be used to prepare the 0.01M solution of oxalic acid, which was employed in the mobile phase in liquid chromatographic studies.