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Arsenic acid or arsoric acid is the chemical compound with the formula H 3 AsO 4. More descriptively written as AsO(OH) 3, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but is only found in solution, where it is largely ionized.
Arsenic forms colorless, odorless, crystalline oxides As 2 O 3 ("white arsenic") and As 2 O 5 which are hygroscopic and readily soluble in water to form acidic solutions. Arsenic(V) acid is a weak acid and the salts are called arsenates , [ 5 ] the most common arsenic contamination of groundwater , and a problem that affects many people.
In deoxygenated water, with low pe, arsenite species dominate. [16] [17] Depending on the pH, arsenate can be found as trihydrogen arsenate (that is arsenic acid H 3 AsO 4), dihydrogen arsenate (H 2 AsO − 4), hydrogen arsenate (HAsO 2− 4), or arsenate (AsO 3− 4). [18] Trihydrogen arsenate is also known as arsenic acid.
Arsenic contaminated water typically contains arsenous acid and arsenic acid or their derivatives. Their names as "acids" is a formality; these species are not aggressive acids but are merely the soluble forms of arsenic near neutral pH. These compounds are extracted from the underlying rocks that surround the aquifer.
Bioremediation of ground water contaminated with arsenic aims to convert arsenite, the toxic form of arsenic to humans, to arsenate. Arsenate (+5 oxidation state) is the dominant form of arsenic in surface water, while arsenite (+3 oxidation state) is the dominant form in hypoxic to anoxic environments.
Disodium hydrogen arsenate is highly toxic. The salt is the conjugate base of arsenic acid. It is a white, water-soluble solid. [1] Being a diprotic acid, its acid-base properties is described by two equilibria: H 2 AsO − 4 + H 2 O ⇌ HAsO 2− 4 + H 3 O + (pK a2 = 6.94) HAsO 2− 4 + H 2 O ⇌ AsO 3− 4 + H 3 O + (pK a3 = 11.5)
Arsenic is a moderately abundant element in Earth's crust, and although many arsenic compounds are often considered highly toxic to most life, a wide variety of organoarsenic compounds are produced biologically and various organic and inorganic arsenic compounds are metabolized by numerous organisms.
Like all arsenic-containing compounds, arsonic acids are toxic and carcinogenic to humans. [1] [2] Arsonic acid refers to H 3 As O 3, the case where the substituent is a single hydrogen atom. The other arsonic acids can simply be viewed as hydrocarbyl derivatives of this base case. Arsenic acid results when the substituent is a hydroxyl group.