Potassium hydrogenoxalate
chemical compound
Potassium hydrogenoxalate 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: Salt of sorrel, sorrel salt, sel d'oseille, sal acetosella; or, inaccurately, salt of lemon (due to the similar acidic “lemony” taste of the edible common sorrel or garden sorrel)
Potassium hydrogenoxalate occurs in some plants, notably sorrel. It is a commercial product used in photography, marble grinding, and removing ink stains.
Properties
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" K+[C2HO4]−·C2H2O4 forms and precipitates out of solution.
The monohydrate KHC2O4·H2O starts losing the water at 100 °C.
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.
Toxicity
Potassium hydrogenoxalate is strongly irritating to eyes, mucoses and gastrointestinal tract.
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