- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Density
- Solubility
- Other properties
- Risks
- Obtaining
- Applications
- As a microbicide and disinfectant in multiple applications
- To disinfect drinking water
- For contact lens care
- In various applications
- References
The sodium chlorite is an inorganic solid consisting of a sodium ion Na + and a chlorite ion ClO 2 -. Its chemical formula is NaClO 2. It is a white crystalline solid, in addition to being a strong oxidizing agent. Therefore it must be handled with great care.
Its main use is as a disinfecting agent for many applications. It allows to eliminate microbes on surfaces such as floors, walls and laboratory equipment in hospitals and clinics and in their water systems.
Solid NaClO 2 sodium chlorite. Author: Chemicalinterest. Source: Wikimedia Commons.
Also in agricultural and veterinary facilities, to sanitize incubators for poultry eggs, to control udder infections of dairy cows, to disinfect water systems for animals, etc.
In the food industry, its acidified aqueous solutions are used to wash meat, chickens, fruits, vegetables, as well as the equipment of such facilities.
With sodium chlorite, chlorine dioxide ClO 2 can be prepared at the site of use, which eliminates microbes, bad smells and tastes from the water so that it is pleasant and can be drunk without problems.
It is also used to bleach paper pulp, vegetable textile fibers and oils, among other applications.
Solid NaClO 2 must be handled with caution, as in contact with certain materials explosions can occur. Their solutions are a bit easier to handle but are very oxidizing and corrosive.
Structure
Sodium chlorite is formed by a sodium cation Na + and a chlorite anion ClO 2 - therefore they are linked by an ionic bond.
The chlorite anion has one chlorine atom in an oxidation state of +3 and two oxygen atoms with valence -2 each. For this reason the chlorite anion has a negative charge.
It also has an angle-shaped structure.
Structure of sodium chlorite NaClO 2. Author: Marilú Stea.
Nomenclature
- Sodium chlorite
- Sodium chlorite
- Sodium salt of chlorous acid
Properties
Physical state
Crystalline white solid.
Molecular weight
90.44 g / mol.
Melting point
It decomposes as it melts between 180 and 200ºC.
Density
2.468 g / cm 3
Solubility
Soluble in water: 64 g / 100 g of water at 17 ºC. Slightly soluble in methanol.
Other properties
It is slightly hygroscopic.
It is a strong oxidizing agent. Reacts violently with combustible and reducing materials. Reacts violently with acids, generating chlorine dioxide ClO 2.
Its alkaline solutions (means in the presence of, for example, NaOH) are quite stable, while in an acid medium chlorous acid HClO 2 is formed, which decomposes quickly:
4 HClO 2 → 2 ClO 2 ↑ + ClO 3 - + Cl - + 2 H + + H 2 O
Risks
Both solid NaClO 2 and its aqueous solutions are potentially hazardous and require great caution and experience in handling and storage.
Solid NaClO 2 can explode on contact with organic substances including gloves and clothing, spill control materials such as sawdust and waste cotton, as well as oils and greases.
The solid form is therefore very difficult to transport and it is preferred to use it in the form of aqueous solutions.
These solutions are extremely corrosive. They should preferably be kept at a pH above 8, that is, an alkaline pH.
NaClO 2 accelerates the combustion of flammable compounds or materials, to the point that it can form explosive mixtures with them.
If heated, it emits toxic fumes of hydrochloric acid HCl and sodium oxide Na 2 O. If exposed to heat or fire for prolonged periods, it may explode.
Obtaining
It is prepared starting with the chemical or electrochemical reduction of sodium chlorate NaClO 3, in the presence of hydrochloric acid HCl to produce chlorine dioxide ClO 2.
The latter is reacted with hydrogen peroxide H 2 O 2 in aqueous sodium hydroxide solution NaOH and a solution of sodium chlorite NaClO 2 is obtained, which evaporates and the solid crystallizes.
It can also be obtained by passing chlorine dioxide gas ClO 2 through a NaOH solution.
2 ClO 2 + 2 NaOH → NaClO 2 + NaClO 3 + H 2 O
Applications
As a microbicide and disinfectant in multiple applications
It is an ingredient in many products that are used to control bacteria, fungi and algae sludge. The products that contain it for this purpose are used in agriculture, commerce, industry and residences or homes.
Serves as a disinfectant for many types of materials and surfaces.
In agriculture, poultry and similar industries, hard surfaces, equipment, facilities for the incubation of bird eggs, greenhouses for fungi such as mushrooms, and cooling water systems and water for poultry houses are disinfected.
It has veterinary use as a topical disinfectant in the control of dairy cattle mastitis, to submerge the animal's nipples. Mastitis is an infection of the udders of cows.
Sometimes cows udders have to be submerged in sodium chlorite solutions to avoid infection in them. Author: Hans Braxmeier. Source: Pixabay.
It is also used in natural research establishments to decontaminate laboratories.
Commercial, industrial, and medical uses include disinfecting ventilation systems, hard surfaces (such as floors, walls, laboratory equipment), and water systems.
In health care facilities such as clinics and hospitals it is used to decontaminate rooms, corridors, isolation areas and for the sterilization of materials.
It is also useful for sanitizing in establishments where people undergo health treatments with water or spa.
In the food industry it is used as a fumigant to preserve food.
It is used in the form of acidified sodium chlorite. This is produced by adding food grade acid (for example, citric acid, phosphoric acid, malic acid, or sodium acid sulfate) to an aqueous solution of sodium chlorite.
Acidified sodium chlorite has antimicrobial properties and is used as a spray or wash or soak solution for chicken, meats, vegetables, fruits, and seafood. Also in water to freeze chicken or poultry.
In homes, it allows disinfecting hard surfaces, such as floors and bathrooms, heating or air conditioning systems, and swimming pool water circulation systems.
Sodium chlorite NaClO 2 can be used to disinfect swimming pools. Author: AgE Global Group. Source: Pixabay.
Products containing sodium chlorite make it possible to sanitize bathrooms. Author: Michal Jarmoluk. Source: Pixabay.
It is also sold in small sachets along with other compounds to release gas and control odors in homes.
To disinfect drinking water
It is used in the purification of drinking water, it acts as an oxidant, improving the taste and smell of drinking water.
Sodium chlorite is widely used as a precursor for the generation of chlorine dioxide ClO 2 that is used to treat drinking water for human consumption, that is, to eliminate microorganisms, odors and unpleasant tastes and it can be drunk.
To generate ClO 2, HCl can be used:
5 NaClO 2 + 4 HCl → 4 ClO 2 ↑ + 5 NaCl + 2 H 2 O
ClO 2 is an antimicrobial agent with a high oxidizing action and a broad spectrum. That is, it acts against a large number of microorganisms.
Microorganisms are inactivated because ClO 2 interferes with important microorganism enzymes and with cell membrane proteins. It also has the advantage that it does not produce organochlorine compounds, which are toxic.
There are sodium chlorite tablets for sale mixed with other compounds which dissolve in water and immediately produce ClO 2 in a controlled way, thus disinfecting the water.
Sodium chlorite is used with other compounds to make ready-to-drink drinking water. Author: Ulrike Leone. Source: Pixabay.
The main problem with treating water to remove flavors and odors with ClO 2 is that toxic chlorite and chlorate salts can form during treatment.
For contact lens care
NaClO 2 is a component of solutions used to disinfect contact lenses.
A combination of NaClO 2 and traces (very small amounts) of hydrogen peroxide H 2 O 2 is used.
The H 2 O 2 stabilizes the ClO 2 that is formed and the combination of both is very effective against bacteria, fungi and yeasts. The resulting products are sodium chloride NaCl, water and oxygen, which are harmless, which means that they are not harmful to the eye.
When the lenses are removed from solution, the residual NaClO 2 rapidly decomposes into NaCl and O 2. Residual peroxide does not irritate the eye. Therefore these solutions are very safe.
Solutions to disinfect contact lenses have sodium chlorite among their ingredients. Author: Nieuw ~ commonswiki. Source: Wikimedia Commons.
In various applications
Sodium chlorite is used for the preparation of chlorine dioxide ClO 2 for immediate use in a large number of applications, some of which were discussed in previous paragraphs.
It is used to whiten wood pulp, textiles such as cotton, vegetable fibers, edible and inedible oils, fats, varnishes, lacquers and waxes.
It is a component of eye drops and some mouthwash solutions.
It is used in the leather processing industry and in metal electrodeposition agents (metal coating).
References
- Williams, L. et al. (2019). Microbiology, Lens Care and Maintenance. In Contact Lenses (Sixth Edition). Recovered from sciencedirect.com.
- US National Library of Medicine. (2019). Sodium chlorite. Recovered from pubchem.ncbi.nlm.nih.gov.
- Gray, NF (2014). Chlorine Dioxide. Process Technology. In Microbiology of Waterborne Diseases (Second Edition). Recovered from sciencedirect.com.
- McKeen, L. (2012). Introduction to Food Irradiation and Medical Sterilization. Chlorine dioxide. In The Effect of Sterilization on Plastic and Elastomers (Third Edition). Recovered from sciencedirect.com.
- Ortenberg, E. and Telsch, B. (2003). Taste and odor problems in drinking water. In Handbook of Water and Wastewater Microbiology. Recovered from sciencedirect.com.
- Karsa, DR (2007). Biocides. Chlorine Dioxide. In Handbook for Cleaning / Decontamination of Surfaces. Recovered from sciencedirect.com.
- Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
- Ullmann's Encyclopedia of Industrial Chemistry. (1990). Fifth Edition. VCH Verlagsgesellschaft mbH.