Oxalate ion (C₂O₄²⁻)
- Charge
- −2
- Atoms
- C × 2, O × 4
- Atoms in total
- 6
- Mass of the ion
- 88.018 g/mol
Oxalate is two carbon atoms bonded to each other, each also bonded to two oxygen atoms, with a 2− charge. It forms when oxalic acid, H₂C₂O₄, loses both of its hydrogen ions. Spinach, rhubarb leaves and tea contain oxalate, and calcium oxalate is the most common material in kidney stones.
- Oxalic acid, and so the -ate ion oxalate, is named after wood sorrel plants of the genus Oxalis, where the acid was first found.
- Oxalate grips metal ions such as iron and calcium, which is why oxalic acid can lift rust stains.
- Calcium oxalate, CaC₂O₄, barely dissolves in water, so it forms crystals in plants and stones in kidneys.