Sodium selenite

Structural formula
General
Surname	Sodium selenite
other names	Sodium selenate (IV)
Molecular formula	Na 2 SeO 3
Brief description	colorless, odorless, moisture-sensitive powder
External identifiers / databases
CAS number 10102-18-8 26970-82-1 (pentahydrate) PubChem 24934 Wikidata Q414626
properties
Molar mass	172.94 g mol −1
Physical state	firmly
density	3.4 g cm −3
Melting point	320 ° C (decomposition)
solubility	good in water (950 g l −1 at 20 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 300 + 330-315-319-317-411 EUH: 031 P: 260-280-301 + 330 + 331 + 310-304 + 340 + 310-305 + 351 + 338-403 + 233
MAK	0.02 mg m −3 (measured as the inhalable aerosol fraction)
Toxicological data	7 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Sodium selenite is the sodium salt of selenious acid (H ₂ SeO ₃ ) with the chemical formula Na ₂ SeO ₃ . It is in the form of needle-shaped, white, hygroscopic crystals.

Occurrence

Sodium selenite occurs naturally in animal tissue.

Extraction and presentation

The salt can be obtained by dissolving selenium dioxide in sodium hydroxide solution , whereby the selenous acid formed by the reaction of the selenium dioxide with water reacts with the sodium hydroxide to form sodium selenite:

${\displaystyle \mathrm {SeO_{2}+\ H_{2}O\rightarrow H_{2}SeO_{3}} }$

${\displaystyle \mathrm {H_{2}SeO_{3}+2\ NaOH\rightarrow Na_{2}SeO_{3}+2\ H_{2}O} }$

Net response:

${\displaystyle \mathrm {SeO_{2}+2\ NaOH\rightarrow Na_{2}SeO_{3}+H_{2}O} }$

properties

Physical Properties

Sodium selenite is a colorless, odorless, moisture-sensitive solid. It has a monoclinic crystal structure with the space group P 2 ₁ / a (space group no. 14, position 3) .

The standard enthalpy of formation for solid sodium selenite is −959 kJ / mol for the anhydrous salt and −2404 kJ / mol for the pentahydrate.

The selenite ion has a pyramidal structure with C _3v symmetry , the distance between the oxygen and selenium atom is 1.74 Å .

The pentahydrate releases its water of crystallization at approx. 40 ° C.

Chemical properties

Red amorphous selenium is very easily split off from sodium selenite by reducing agents .

use

Sodium selenite is used to color glass and porcelain red (reduction to red selenium), as a component of fixing baths and to test the germination of seeds. It is also used in very low concentrations (50–1000 µg) in medicine for selenium deficiency symptoms ( Keshan's disease ), in cancer therapy and as an additive in animal nutrition. It also serves as a detection reagent for alkaloids .

In Sweden in plastic embedded sodium selenite for precipitation of mercury ions as insoluble mercury selenide used in lakes.

safety instructions

Sodium selenite is used as an inorganic compound in food supplements according to the applicable European guidelines. Critics claim that this inorganic compound can lead to increased levels of mercury in the organism and is therefore harmful. Investigations by the Federal Institute for Risk Assessment as well as the results of other studies invalidate these concerns and do not reveal any advantage in replacing inorganic selenites in food supplements with organic compounds such as selenium yeast or selenomethionine. The opposite is the case, because so far no constant quality can be guaranteed for selenium yeast. Organic selenium compounds such as selenium yeast must therefore not be used in food supplements.

See also

• Sodium selenide Na ₂ Se
• Sodium selenate Na ₂ SeO ₄

Individual evidence

1. ↑ ^{a b c d e f g} Entry on sodium selenite in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
2. ^ ^{A b} Jean D'Ans, Ellen Lax: Paperback for chemists and physicists . Springer DE, 1997, ISBN 3-540-60035-3 , pp. 626 ( limited preview in Google Book search).
3. ↑ Entry on sodium selenite in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
4. ↑ Sodium selenite data sheet (PDF) from Fisher Scientific , accessed on February 13, 2014.
5. ↑ Sodium selenite at MeriMed ( Memento of the original from June 29, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
6. ↑ G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 431-432.
7. ^ GH Aylward, TJV Findlay: data collection chemistry in SI units . 3. Edition. Wiley-VCH, 1999, ISBN 3-527-29468-6 .
8. ↑ Selenium compounds in food. BfR opinion No. 015/2005 of December 17, 2004

literature

• AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 .
• Collective of authors: Inorganikum . 5th edition. VEB Deutscher Verlag der Wissenschaften Berlin 1973.
• Entry to sodium selenite. In: Römpp Online . Georg Thieme Verlag, accessed on November 12, 2014.