NaHC2O4

Sodium hydrogen oxalate, also known as sodium binoxalate or sodium acid oxalate, has the chemical formula NaHC2O4. It is the sodium salt of oxalic acid, where one of the acidic protons has been replaced by a sodium ion. In its pure form, it is a white crystalline solid.

This compound is often encountered in laboratory settings as a primary standard for acid-base titrations. Its purity, stability, and well-defined stoichiometry make it suitable for calibrating burettes and determining the concentration of basic solutions. It can be prepared by reacting oxalic acid with an equimolar amount of sodium hydroxide or sodium carbonate.

Sodium hydrogen oxalate is soluble in water, forming an acidic solution due to the presence of the hydrogen oxalate ion (HC2O4-), which can act as a weak acid. The hydrogen oxalate ion itself is an intermediate species in the dissociation of oxalic acid. The compound can be distinguished from other sodium oxalate salts by its acidic properties. It finds applications in cleaning and rust removal due to the properties of the oxalate ion.