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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.
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. These pK a values are close to those for phosphoric acid. The highly basic arsenate ion (AsO 3− 4) is the product of the third ionization. Unlike phosphoric acid, arsenic acid is an oxidizer, as illustrated by its ...
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.
Trihydrogen arsenate is also known as arsenic acid. At a given pH, the distribution of these arsenate species can be determined from their respective acid dissociation constants. [17] H 3 AsO 4 + H 2 O ⇌ H 2 AsO − 4 + [H 3 O] + (pK a1 = 2.19) 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 ...
The main factors are pH and the redox potential. Generally, the main forms of arsenic under oxic conditions are H 3 AsO 4, H 2 AsO − 4, HAsO 2− 4, and AsO 3− 4 at pH 2, 2–7, 7–11 and 11, respectively. Under reducing conditions, H 3 AsO 4 is predominant at pH 2–9. Oxidation and reduction affects the migration of arsenic in subsurface ...
Arsenate is the major arsenic form in oxidizing environments; however, in one study, bacteria from arsenic-contaminated soil at a smelter site was able to reduce As(+5) to As(+3) under anaerobic conditions at arsenic concentration as high as 75 mg/L. [3] Arsenate-respiring bacteria and Archaea have also recently been isolated from a diversity of natural environments, including freshwater ...
In gastroenterology, esophageal pH monitoring is the current gold standard for diagnosis of gastroesophageal reflux disease (GERD). It provides direct physiologic measurement of acid in the esophagus and is the most objective method to document reflux disease, assess the severity of the disease and monitor the response of the disease to medical or surgical treatment.
Arsenic (III) enters the cells though aquaporins 7 and 9, which is a type of aquaglyceroporin. [26] Arsenic (V) compounds use phosphate transporters to enter cells. [26] The arsenic (V) can be converted to arsenic (III) by the enzyme purine nucleoside phosphorylase. [26]