Oxalic acid is an organic compound with the formula C2H2O4. It is a colorless crystalline solid that forms a colorless solution in water. Its condensed formula is HOOCCOOH, reflecting its classification as the simplest dicarboxylic acid.
Its acid strength is much greater than that of acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate(C
4), is a chelating agent for metal cations. Typically, oxalic acid occurs as the dihydrate with the formula C2H2O4·2H2O.
|Molar mass||90.03 g·mol−1
126.065 g mol−1 (dihydrate)
|Density||1.90 g cm−3 (anhydrous)
1.653 g cm−3 (dihydrate)
|Melting point||189 to 191 °C (372 to 376 °F; 462 to 464 K)
101.5 °C (214.7 °F; 374.6 K) dihydrate
|143 g/litre (25 °C)|
|Solubility||237 g/litre (15 °C) in ethanol
14 g/litre (15 °C) in diethyl ether 
|Vapor pressure||<0.001 mmHg (20 °C)|
|Acidity (pKa)||1.25, 4.14|