Oxalic acid

Oxalic acid found in lettuce, cabbage, cauliflower (especially broccoli), green beans, green beans and in small amounts in most vegetables and fruits.
Oxalic acid is a dicarboxylic acid which consists of only two C atoms in each molecule, so that the two carboxylate groups are contiguous. Because the location of the adjacent carboxylate groups, oxalic acid has a dissociation constant that is greater than other organic acids.
General properties of Oxalic Acid
Oxalic acid in a state of pure form of crystalline compounds, soluble in water (8% at 10o C) and soluble in alcohol. Oxalic acid forms neutral salts with alkali metals (NAK), which is soluble in water (5-25%), while that with the alkaline earth metals, including Mg or with heavy metal, has a very small solubility in water. So the calcium oxalate is practically insoluble in water. Based on these properties of oxalic acid is used to determine the amount of calcium. Oxalic acid is ionized in strong acid media.