Sodium selenite
3D model (JSmol)
ECHA InfoCard 100.030.230 Edit this at Wikidata
EC Number
  • 233-267-9
RTECS number
  • VS7350000
UN number 2630
  • InChI=1S/2Na.H2O3Se/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 checkY
  • InChI=1/2Na.H2O3Se/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2
  • [Na+].[Na+].[O-][Se]([O-])=O
Molar mass 172.948 g·mol−1
Appearance colourless solid
Density 3.1 g/cm3
Melting point decomposes at 710 °C
85 g/100 mL (20 °C)
Solubility insoluble in ethanol
A12CE02 (WHO) (Oral), B05XA20 (WHO) (Parenteral)
GHS labelling:
GHS06: ToxicGHS07: Exclamation markGHS09: Environmental hazard
H300, H317, H331, H411
P261, P264, P270, P271, P272, P273, P280, P301+P310, P302+P352, P304+P340, P311, P321, P330, P333+P313, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
Safety data sheet (SDS) ICSC 0698
Related compounds
Related compounds
Sodium sulfite
Sodium selenate
Sodium selenide
sodium biselenite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium selenite is the inorganic compound with the formula Na2SeO3. This salt is a colourless solid. The pentahydrate Na2SeO3(H2O)5 is the most common water-soluble selenium compound.

Synthesis and fundamental reactions

Sodium selenite usually is prepared by the reaction of selenium dioxide with sodium hydroxide:[1]

SeO2 + 2 NaOH → Na2SeO3 + H2O

The hydrate converts to the anhydrous salt upon heating to 40 °C.

According to X-ray crystallography, both anhydrous Na2SeO3 and its pentahydrate feature pyramidal SeO32−. The Se-O distances range from 1.67 to 1.72 Å.[2] Oxidation of this anion gives sodium selenate, Na2SeO4.[3]


Together with the related barium and zinc selenites, sodium selenite is mainly used in the manufacture of colorless glass. The pink color imparted by these selenites cancels out the green color imparted by iron impurities.[4]

Because selenium is an essential element, sodium selenite is an ingredient in dietary supplements such as multi-vitamin/mineral products, but supplements that provide only selenium use L-selenomethionine or a selenium-enriched yeast.

The US Food and Drug Administration approved a selenium supplement to animal diets; the most common form is sodium selenite for pet foods. According to one article, "not much was known about which selenium compounds to approve for use in animal feeds when the decisions were made back in the 1970s .. At the time the regulatory action was taken, only the inorganic selenium salts (sodium selenite and sodium selenate) were available at a cost permitting their use in animal feed.” [5]

Sodium selenite has been proposed as an effective suicide agent.[6]


Selenium is toxic in high concentrations. As sodium selenite, the chronic toxic dose for human beings was described as about 2.4 to 3 milligrams of selenium per day.[7] In 2000, the US Institute of Medicine set the adult Tolerable upper intake levels (UL) for selenium from all sources - food, drinking water and dietary supplements - at 400 μg/day.[8] The European Food Safety Authority reviewed the same safety question and set its UL at 300 μg/day.[9]

See also


  1. ^ F. Féher, "Sodium Selenite" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 432.
  2. ^ Wickleder MS (2002). "Sodium Selenite, Na2SeO3". Acta Crystallographica Section E. 58 (11): i103–i104. Bibcode:2002AcCrE..58I.103W. doi:10.1107/S1600536802019384. ISSN 1600-5368.
  3. ^ Mereiter K (2013). "Sodium Selenite Pentahydrate, Na2SeO3·5H2O". Acta Crystallographica Section E. 69 (11): i77–i78. doi:10.1107/S1600536813028602. PMC 3884237. PMID 24454013.
  4. ^ Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry (published on-line in 2000) Wiley-VCH, Weinheim, 2002 doi:10.1002/14356007.a23_525
  5. ^ Schrauzer GN (2001). "Nutritional selenium supplements: product types, quality, and safety". Journal of the American College of Nutrition. 20 (1): 1–4. doi:10.1080/07315724.2001.10719007. PMID 11293463. S2CID 12668227.
  6. ^ Nitschke, Philip (28 February 2016). The peaceful pill ehandbook. Stewart, Fiona, 1966- (January 2021 ed.). Bellingham, WA. p. 192. ISBN 978-0-9758339-1-9. OCLC 1003529499.((cite book)): CS1 maint: location missing publisher (link)
  7. ^ Wilber CG (1980). "Toxicology of selenium". Clinical Toxicology. 17 (2): 171–230. doi:10.3109/15563658008985076. PMID 6998645.
  8. ^ Institute of Medicine (2000). "Selenium". Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: The National Academies Press. pp. 284–324. doi:10.17226/9810. ISBN 978-0-309-06935-9. PMID 25077263.
  9. ^ Tolerable Upper Intake Levels For Vitamins And Minerals (PDF), European Food Safety Authority, 2006