Calcium salt of oxalic acid / From Wikipedia, the free encyclopedia
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|Molar mass||128.096 g·mol−1|
|Appearance||colourless or white crystals (anhydrous and hydrated forms)|
|Density||2.20 g/cm3, monohydrate|
|Melting point||200 °C (392 °F; 473 K) decomposes (monohydrate)|
|0.61 mg/100 g H2O (20 °C)|
Solubility product (Ksp)
|2.7 × 10−9 for CaC2O4|
|Occupational safety and health (OHS/OSH):|
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula CaC2O4. It forms hydrates CaC2O4·nH2O, where n varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate CaC2O4·H2O occurs naturally as the mineral whewellite, forming envelope-shaped crystals, known in plants as raphides. The two rarer hydrates are dihydrate CaC2O4·2H2O, which occurs naturally as the mineral weddellite, and trihydrate CaC2O4·3H2O, which occurs naturally as the mineral caoxite, are also recognized. Some foods have high quantities of calcium oxalates and can produce sores and numbing on ingestion and may even be fatal. Cultural groups with diets that depend highly on fruits and vegetables high in calcium oxalate, such as those in Micronesia, reduce the level of it by boiling and cooking them. They are a constituent in 76% of human kidney stones. Calcium oxalate is also found in beerstone, a scale that forms on containers used in breweries.