Hydrogenoxalate

Structural formula of the hydrogenoxalate anion, showing the carboxylic acid group connected to a carboxylate group.

Hydrogenoxalate, also spelled hydrogen oxalate and historically known as bioxalate, is an ion with the chemical formula HC2O−4. It is a conjugate base of oxalic acid and conjugate acid of oxalate, found in moderately acidic solution.