Sodium selenite is the
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemi ...
with the formula Na
2SeO
3. This
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quanti ...
is a colourless solid. The pentahydrate Na
2SeO
3(H
2O)
5 is the most common water-soluble
selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and telluriu ...
compound.
Synthesis and fundamental reactions
Sodium selenite usually is prepared by the reaction of
selenium dioxide with
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkal ...
:
:SeO
2 + 2 NaOH → Na
2SeO
3 + H
2O
The hydrate converts to the anhydrous salt upon heating to 40 °C.
According to
X-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angle ...
, both anhydrous Na
2SeO
3 and its pentahydrate feature pyramidal SeO
32−. The Se-O distances range from 1.67 to 1.72 Å.
Oxidation of this anion gives sodium selenate, Na
2SeO
4.
Applications
Together with the related
barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
...
and
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...
selenites, sodium selenite is mainly used in the manufacture of colorless
glass
Glass is a non-Crystallinity, crystalline, often transparency and translucency, transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most ...
. The pink color imparted by these selenites cancels out the green color imparted by
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
impurities.
Because selenium is an
essential element, sodium selenite is an ingredient in
dietary supplement
A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources or that are synthetic in orde ...
s 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
The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
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.”
Sodium selenite has been proposed as an effective
suicide
Suicide is the act of intentionally causing one's own death. Mental disorders (including depression, bipolar disorder, schizophrenia, personality disorders, anxiety disorders), physical disorders (such as chronic fatigue syndrome), and ...
agent.
Safety
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. In 2000, the U.S. 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.
The
European Food Safety Authority
The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002 ...
reviewed the same safety question and set its UL at 300 μg/day.
See also
*
Selenite (ion)
References
External links
Linus Pauling Institute page on selenium
{{Prostanoidergics
Hazardous air pollutants
Selenites
Sodium compounds
Dietary minerals
Dietary supplements