Sodium selenite
Encyclopedia
Sodium selenite is a salt, a colourless solid, and the most common water-soluble selenium
compound. It has the formula
s Na
2SeO
3 and Na2SeO3(H2O)5 (CAS#26970-82-1). Respectively, these are the anhydrous
salt and its pentahydrate
. This hydrate
d salt is the more common one. The hydrated and anhydrous salts behave identically for most purposes, although their molar masses differ.
with sodium hydroxide:
Acidification of selenium dioxide gives selenous acid
, which, unlike sulfurous acid
, can be isolated at room temperature.
Akin to the related salt sodium sulfite
, Na2SeO3 features a pyramidal dianion SeO with a trigonal (C3v) symmetry. Oxidation of this anion gives sodium selenate, Na2SeO4.
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.
Because selenium is an essential element, sodium selenite is an ingredient in some food supplements.
The US Food and Drug Administration
approved a selenium supplement to animal diets, however 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.”
dose for human beings is about 2.4 to 3 milligrams of selenium per day.
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
compound. It has the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
s Na
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
2SeO
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
3 and Na2SeO3(H2O)5 (CAS#26970-82-1). Respectively, these are the anhydrous
Anhydrous
As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another...
salt and its pentahydrate
Water of crystallization
In crystallography, water of crystallization or water of hydration or crystallization water is water that occurs in crystals. Water of crystallization is necessary for the maintenance of crystalline properties, but capable of being removed by sufficient heat...
. This hydrate
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
d salt is the more common one. The hydrated and anhydrous salts behave identically for most purposes, although their molar masses differ.
Synthesis and fundamental reactions
Sodium selenite usually is prepared by the reaction of selenium dioxideSelenium dioxide
Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium.-Properties:...
with sodium hydroxide:
- SeO2 + 2 NaOH → Na2SeO3 + H2O
Acidification of selenium dioxide gives selenous acid
Selenous acid
Selenous acid is the chemical compound with the formula H2SeO3. Structurally, it is more accurately described by 2SeO. It is the principal oxoacid of selenium; the other being selenic acid.-Formation and properties:...
, which, unlike sulfurous acid
Sulfurous acid
Sulfurous acid is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase...
, can be isolated at room temperature.
Akin to the related salt sodium sulfite
Sodium sulfite
Sodium sulfite is a soluble sodium salt of sulfurous acid. It is a product of sulfur dioxide scrubbing, a part of the flue gas desulfurization process...
, Na2SeO3 features a pyramidal dianion SeO with a trigonal (C3v) symmetry. Oxidation of this anion gives sodium selenate, Na2SeO4.
Applications
Together with the related bariumBarium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
and zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
selenites
Selenite (ion)
The selenite anion is a selenium oxoanion with the chemical formula SeO32−.A selenite is a compound that contains this ion....
, sodium selenite is mainly used in the manufacture of colorless glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
. The pink color imparted by these selenites cancels out the green color imparted by iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
impurities.
Because selenium is an essential element, sodium selenite is an ingredient in some food supplements.
The US Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
approved a selenium supplement to animal diets, however 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.”
Safety
Selenium is toxic in high concentrations. The chronic toxicChronic toxicity
Chronic toxicity is a property of a substance that has toxic effects on a living organism, when that organism is exposed to the substance continuously or repeatedly. Compared with acute toxicity.Two distinct situations need to be considered:...
dose for human beings is about 2.4 to 3 milligrams of selenium per day.