Sodium oxalate (Na2C2O4) structure, properties, uses, risks

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Philip Kelley

The sodium oxalate It is an organic compound made up of two sodium ions and one oxalate ion. Its chemical formula is NatwoCtwoOR4 or also Natwo(COO)two. It is the sodium salt of oxalic acid or ethanedioic acid. The NatwoCtwoOR4 is a white crystalline solid and its aqueous solutions are basic (alkaline).

Sodium oxalate is present in plants and vegetables. In humans, oxalic acid is generated naturally from its conjugated acid, which in turn is produced by certain metabolic processes.

Sodium oxalate Natwo(COO)two solid. Leiem [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. Source: Wikimedia Commons.

The NatwoCtwoOR4 It is used in chemical analysis laboratories as a reducing agent (the opposite of oxidant). Also to allow testing of certain organic compounds during wastewater treatment.

It has been used for the disposal of chlorofluorocarbons (CGC) waste, which damage the ozone layer. It is also a raw material to obtain oxalic acid economically.

Due to the high sodium oxalate content of some edible vegetables, people who have a tendency to form stones or kidney stones should avoid consuming such foods. This is because the stones are usually formed with oxalates..

Article index

  • 1 Structure
  • 2 Nomenclature
  • 3 Properties
    • 3.1 Physical state
    • 3.2 Molecular weight
    • 3.3 Density
    • 3.4 Solubility
    • 3.5 pH
    • 3.6 Chemical properties
  • 4 Obtaining
    • 4.1 Presence in nature
  • 5 Uses
    • 5.1 In chemical analysis laboratories
    • 5.2 In the destruction of chlorofluorocarbons
    • 5.3 In determining important parameters in wastewater treatment
    • 5.4 To obtain oxalic acid
    • 5.5 To remove unwanted compounds
  • 6 Risks
  • 7 References

Structure

Sodium oxalate is made up of two sodium cations Na+ and an oxalate anion (COO)twotwo-. The oxalate anion is in turn made up of two COO units- bonded through the two carbon atoms: -OOC-COO-.

In solid sodium oxalate, the oxalate anion has a flat shape. This means that both carbons and oxygens are in the same plane..

Chemical structure of sodium oxalate Natwo(COO)two. Author: Benjah-bmm27. Source: Wikimedia Commons.

Nomenclature

- Sodium oxalate

- Disodium oxalate

- Ethanedioic acid sodium salt

Properties

Physical state

Solid white crystalline.

Molecular weight

134.0 g / mol

Density

2.27 g / cm3 at 20 ° C.

Solubility

Soluble in water: 3.7 g / 100 mL at 20 ° C.

pH

Its aqueous solutions are basic (alkaline) because the oxalate anion tends to take protons from the water, leaving the OH ions free.-.

Chemical properties

It can neutralize acids and the reactions are exothermic, that is, they give off heat.

It serves as a reducing agent and in these reactions generates carbon dioxide COtwo.

It has the property of strongly binding to various metal ions such as ferrous iron ions Fetwo+ and ferric Fe3+.

Obtaining

According to a consulted source, sodium oxalate can be obtained by oxidizing carbon with oxygen Otwo at a temperature of about 250 ° C in a concentrated solution of sodium hydroxide NaOH.

Presence in nature

Sodium oxalate is present in many plants and vegetables, such as chard, spinach, and rhubarb, and in grains such as soybeans, among many other plant products..

Spinach has a large amount of sodium oxalate. Author: Aline Ponce. Source: Pixabay.

Its conjugated acid, oxalic acid, is produced in the human body by the metabolism of glycolic acid or ascorbic acid. Once produced, it is not metabolized, but is excreted in the urine in the form of oxalate..

Rhubarb contains sodium oxalate. Authors: S. Hermann & F. Richter. Source: Pixabay.

Applications

In chemical analysis laboratories

It is used as a chemical reagent, generally as a reducing agent, for example for the standardization of potassium permanganate solutions, that is, to determine exactly how much sodium permanganate they have.

In the destruction of chlorofluorocarbons

Sodium oxalate has been used for the destruction of chlorofluorocarbons (CFCs). These CFC compounds have been one of those responsible for the destruction of the planet's ozone layer (which protects us from ultraviolet radiation).

In 1996, some researchers proposed the use of sodium oxalate to eliminate them, as it easily reacts with CFCs at temperatures of 270-290 ° C, making them harmless to the ozone layer..

The reaction of sodium oxalate with CFCs can be controlled to obtain halogenated aromatic hydrocarbons that are not harmful to the ozone layer but are useful compounds in the chemical industry..

Said reaction can also be maximized and convert all CFC into sodium fluoride NaF, sodium chloride NaCl, elemental carbon and carbon dioxide CO.two.

The planet's ozone layer protects us from the sun's ultraviolet rays. Sodium oxalate eliminates the CFC compounds that damage it. Author: One94. Source: Pixabay.

In determining important parameters in wastewater treatment

Sodium oxalate has been found to be useful in measuring the amount and kinds of organic compounds secreted by microorganisms from sludge used to treat wastewater..

The measurement of such compounds is important to determine their function during wastewater treatment, since the ease of separating the sludge from the water depends on them..

Using sodium oxalate avoids the disadvantages of other methods.

To obtain oxalic acid

Crude sodium oxalate from certain process wastes has been used to produce oxalic acid HtwoCtwoOR4 in great quantities.

The method uses sludge from the Bayer process to treat bauxite (an aluminum ore). In the Bayer process, bauxite is treated with sodium hydroxide NaOH to dissolve the alumina of this mineral.

In the process of dissolving alumina, certain organic compounds present in the mineral, such as humic acids, are attacked by NaOH, generating a large amount of sodium oxalate NatwoCtwoOR4.

This sodium oxalate is incorporated into a mud with aluminum compounds. To purify it, the whole is dissolved, filtered and passed through an ion exchange column of the acid type..

In the column is a sulfonic acid resin RSO3H where metal ions are exchanged Na+ by hydrogen ions H+, so you get oxalic acid HtwoCtwoOR4.

RSO3H + NatwoCtwoOR4 ⇔ RSO3Na + NaHCtwoOR4

RSO3H + NaHCtwoOR4 ⇔ RSO3Na + HtwoCtwoOR4

This is an inexpensive process and the oxalic acid obtained is of acceptable purity..

To remove unwanted compounds

Conjugated acid of sodium oxalate, oxalic acid HtwoCtwoOR4, used to dissolve certain types of debris and scale.

It takes advantage of the characteristic of oxalic acid to convert into oxalate acting as a complexing or precipitating agent, for example during the processing of waste from various nuclear fuels.

Oxalic acid is also used to remove mineral scale and iron oxides in pipes and other equipment, this is due to its ability to bind strongly both the ferrous ion Fetwo+ as to the ferric ion Fe3+ forming oxalates.

Risks

If directly inhaled or ingested sodium oxalate causes pain in the throat, esophagus and stomach. Produces vomiting, severe purging, weak pulse, cardiovascular collapse, neuromuscular symptoms, and kidney damage.

People who have a tendency to form kidney stones due to accumulation of oxalate in the urine should avoid consuming vegetables with a high content of soluble oxalates such as sodium.

Sodium oxalate in high amounts in food when it reaches the urine binds to the calcium present in it and can cause calcium oxalate stones or stones in the kidneys in people who have a tendency to do so..

Sodium oxalate in some foods can lead to kidney stones in people with a predisposition to it. Author: Azwer. Source: Pixabay.

References

  1. U.S. National Library of Medicine. (2019). Sodium oxalate. National Center for Biotechnology Information. Recovered from pubchem.ncbi.nlm.nih.gov.
  2. Chai, W. and Liebman, M. (2005). Effect of Different Cooking Methods on Vegetable Oxalate Content. J. Agric. Food Chem. 2005, 53, 3027-3030. Recovered from pubs.acs.org.
  3. Dagani, R. (1996). CFC Destroying Reaction. Chemical & Engineering News Archive 1996, 74, 4, 6-7. Recovered from pubs.acs.org.
  4. Sajjad, M. and Kim, K.S. (2016). Extraction of extracellular polymeric substances from activated sludge using sodium oxalate. Int. J. Environ. Sci. Technol. 13, 1697-1706 (2016). Recovered from link.springer.com.
  5. Jeffrey, G.A. and Parry, G.S. (1954). The Crystal Structure of Sodium Oxalate. J. Am. Chem. Soc. 1954, 76, 21, 5283-5286. Recovered from pubs.acs.org.
  6. Okuwaki, A. et al. (1984). Production of Oxalate by the Oxidation of Coal with Oxygen in a Concentrated Sodium Hydroxide Solution. Ind. Eng. Chem. Prod. Res. Dev. 1984, 23, 648-651. Recovered from pubs.acs.org.
  7. Hefter, G. et al. (2018). Solubility of Sodium Oxalate in Concentrated Electrolyte Solutions. J Chem & Eng Data. 2018, 63, 3, 542-552. Recovered from pubs.acs.org.
  8. The, K. I. (1992). Process for the preparation of oxalic acid and sodium hydrogen oxalate from crude sodium oxalate. U.S. Patent No. 5,171,887. Dec 15, 1992. Recovered from freepatentsonline.com.

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