Arsenate: Difference between revisions

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→‎Ions: "In highly acidic conditions it exists as arsenic acid" define "it"
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(→‎Ions: "In highly acidic conditions it exists as arsenic acid" define "it")
 
==Ions==
The arsenates are derived from [[arsenic acid]], H<sub>3</sub>AsO<sub>4</sub>. This moderately strong acid converts to '''dihydrogen arsenate''' ({{chem|H|2|AsO|4|−}}), '''hydrogen arsenate''' ({{chem|HAsO|4|2−}}), and arsenate ({{chem|AsO|4|3−}}), depending on pH. The quantitative relationship between these species is defined by the acid dissociation constants:
* In highly [[acid]]ic conditions it exists as [[arsenic acid]], H<sub>3</sub>AsO<sub>4</sub>;
:H<sub>3</sub>AsO<sub>4</sub> + H<sub>2</sub>O {{eqm}} H<sub>2</sub>AsO{{su|b=4|p=−}} + H<sub>3</sub>O<sup>+</sup> (''K''<sub>1</sub> = 10<sup>−2.19</sup>)
* in moderately acidic conditions it exists as '''dihydrogen arsenate''' ion, {{chem|H|2|AsO|4|−}};
:H<sub>2</sub>AsO{{su|b=4|p=−}} + H<sub>2</sub>O {{eqm}} HAsO{{su|b=4|p=2−}} + H<sub>3</sub>O<sup>+</sup> (''K''<sub>2</sub> = 10<sup>−6.94</sup>)
* in moderately basic conditions it exists as '''hydrogen arsenate''' ion {{chem|HAsO|4|2−}};
:HAsO{{su|b=4|p=2−}} + H<sub>2</sub>O {{eqm}} AsO{{su|b=4|p=3−}} + H<sub>3</sub>O<sup>+</sup> (''K''<sub>3</sub> = 10<sup>−11.5</sup>)
* and finally, in highly basic conditions, it exists as the arsenate ion {{chem|AsO|4|3−}}.
 
These values are similar to those of the hydrogen phosphates. Hydrogen arsenate and dihydrogen arsenate predominate in aqueous solution near neutral pH.
 
== Arsenate poisoning ==