Oxalic Acid

What Does Oxalic Acid Mean?

Oxalic acid is an organic toxic compound with the chemical formula H₂C₂O₄. It belongs to the family of carboxylic acids. It is a colorless crystalline solid that forms a colorless solution in water.

Oxalic acid is widely used for bleaching and removing rusts and stains. When removing rusts, it converts most insoluble iron compounds into a soluble complex ion. Oxalic acid is the prime constituent of many commercial preparations used to remove scale from automobile radiators.

Oxalic acid is also known as ethanedioic acid.

Corrosionpedia Explains Oxalic Acid

Oxalic acid is an organic compound containing carboxylic acids. It is more acidic than acetic acid. The conjugate base of oxalic acid is oxalate (C₂O₄^2-), which is used as a chelating agent for metal cations. Oxalic acid is the most popular electrolytic etching solution to reveal the microstructure of austenitic stainless steels. This is done by an oxalic acid etch test.

Besides bleaching and rust and stain removal, oxalic acid is used as a reducing agent to develop photographic films. It is also used in wastewater treatment to effectively remove calcium.

Oxalic acid in its pure form is very toxic and corrosive. Corrosion rates of metals in oxalic acid with other acids are different. For example, corrosion rates of iron in oxalic acid are generally much less than those in nitric acid. The corrosion rate triples in the same solutions if the temperature is increased to 50 °C (122 °F).

Oxalic acid (OA) is a good corrosion inhibitor for carbon steel, exhibiting good inhibition efficiency (IE) with OA solutions with a pH greater than 3.0, whereas for pH solutions less than 3.0, the corrosion rate is increased.