Potassium hydrogenoxalate

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Potassium hydrogenoxalate
Monopotassium oxalate.png
IUPAC name
Potassium 2-hydroxy-2-oxoacetate
Other names
Potassium bioxalate
3D model (JSmol)
ECHA InfoCard 100.004.431
Molar mass 128.12 g·mol−1
Appearance White crystalline solid
Odor odorless
Density 2.0 g/cm3
2.5 g/100 g
Solubility slightly soluble in alcohol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Potassium hydrogenoxalate, also known as potassium bioxalate, is a salt with formula KHC2O4 or K+·HO2C-CO2. It is one of the most common salts of the hydrogenoxalate anion, and can be obtained by reacting potassium hydroxide with oxalic acid in 1:1 mole ratio.

The salt is also known as potassium hydrogen oxalate, potassium bioxalate, acid potassium oxalate, or monobasic potassium oxalate. In older literature, it was also called sorrel salt, sal acetosella, or (rather improperly) salt of lemon

Potassium hydrogenoxalate occurs in some plants, notably sorrel. It is a commercial product, used in photography, marble grinding, and to remove ink stains.


The anhydrous product is a white, odorless, crystalline solid, hygroscopic and soluble in water (2.5 g/100 g at room temperature). The solutions are basic. Below 50 °C the much less soluble potassium tetraoxalate forms and precipitates out of solution.[1]

The monohydrate KHC2O4·H2O starts losing the water at 100 °C.[2]

The anhydrous salt was found to have remarkable elastic anisotropy, due to its crystal structure that consists of relatively rigid columns of hydrogen-bonded hydrogenoxalate anions, joined into sheets by ionic K–O bonds.[3]


Potassium hydrogenoxalate is strongly irritating to eyes, mucoses and gastrointestinal tract. It may cause cardiac failure and death.[1]

See also[edit]


  1. ^ a b ChemicalBook (2007) Potassium binoxalate Product Description
  2. ^ Mark Dugan (2009) Potassium binoxalate product data sheet. Hummel Croton Inc.
  3. ^ H. Koppers (1973), 'The Elastic Constants of Monoclinic Potassium Hydrogen Oxalate Acta Crystallographica,volume A29, p. 415.