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, or sodium chloride (NaCl), in water would be re ...
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 ). In other words, an oxi ...
; it can be reduced to
selenite or
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 tellurium, ...
.
In strongly acidic conditions, the hydrogen selenate ion, , is formed. It corresponds to the
selenic acid, H
2SeO
4, which is a strong acid and can in its concentrated form dissolve
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...
.
The element selenium exhibits several valence states. Selenate is the least reduced, followed by selenite, and elemental selenium;
selenide 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, bacterium, or plant, as well as the effect on a subs ...
of selenium. Selenate is the form required by organisms that need selenium as a
micronutrient
Micronutrients are essential dietary elements required by organisms in varying quantities throughout life to orchestrate a range of physiological functions to maintain health. Micronutrient requirements differ between organisms; for example, huma ...
. 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 ar, القلوي, al-qaly, lit=ashes of the saltwort) is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale.
Alkalinity is the strength ...
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
Selenium(VI) compounds
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