The selenate ion is .
Selenates are analogous to
sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
s and have similar chemistry. They are highly soluble in
aqueous
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in wat ...
solutions at ambient temperatures.
Unlike sulfate, selenate is a somewhat good
oxidizer
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...
; it can be reduced to
selenite or
selenium
Selenium is a chemical element; it has symbol (chemistry), symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elem ...
.
In strongly acidic conditions, the hydrogen selenate ion, , is formed. It corresponds to the
selenic acid
Selenic acid is the inorganic compound with the formula . It is an oxoacid of selenium, and its structure is more accurately described as . It is a colorless compound. Although it has few uses, one of its salts, sodium selenate is used in the pr ...
, H
2SeO
4, which is a strong acid and can in its concentrated form dissolve
gold
Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
.
The element selenium exhibits several valence states. Selenate is the least reduced, followed by selenite, and elemental selenium;
selenide
A selenide is a chemical compound containing a selenium with oxidation number of −2. Similar to sulfide, selenides occur both as inorganic compounds and as organic derivatives, which are called organoselenium compound.
Inorganic selenides
Th ...
is even more reduced than elemental selenium. The
valence state is an important factor to the
toxicity
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...
of selenium. Selenate is the form required by organisms that need selenium as a
micronutrient
Micronutrients are essential chemicals required by organisms in small quantities to perform various biogeochemical processes and regulate physiological functions of cells and organs. By enabling these processes, micronutrients support the heal ...
. These organisms have the ability to acquire, metabolize and excrete selenium. The level at which selenium becomes toxic varies from species to species and is related to other environmental factors like
pH and
alkalinity
Alkalinity (from ) is the capacity of water to resist Freshwater acidification, acidification. It should not be confused with base (chemistry), basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer s ...
that influence the concentration of selenite over selenate.
Selenate and other forms of selenium are highest in areas where ancient seas have evaporated. These areas are enriched in selenium and over millennia, biologic adaptation has occurred.
References
{{Selenates
Selenium(VI) compounds
Chalcogen oxyanions