Arsenic acid

Structural formula
General
Surname	Arsenic acid
other names	Arsenic (III) acid
Molecular formula	H 3 AsO 3
Brief description	Very weak acid which is stable only in aqueous solution
External identifiers / databases
PubChem	545
DrugBank	DB04456
Wikidata	Q423271
properties
Molar mass	125.94 g mol −1
Physical state	only stable as an aqueous solution
solubility	soluble in water
safety instructions
H and P phrases	H: 331-301-410
	P: ?
MAK	not established as a carcinogen
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Arsenic acid is an arsenic compound with the molecular formula H ₃ AsO ₃ . Their salts are called arsenites. They are obtained by dissolving arsenic (III) oxide in water:

{\ displaystyle {\ ce {As2O3 + 3H2O -> 2H3AsO3}}}

It is a weak tri-protonic acid ( pKa ₁ 9.23, pks ₂ 13.52) that just barely turns litmus paper a pale red color and can be converted to the corresponding esters with alcohols . The salts of arsenic acid are called arsenites . The solubility of arsenic acid increases in an alkaline environment because charged arsenic ions are formed:

{\ displaystyle {\ ce {H3AsO3 + 3OH ^ - -> AsO3 ^ 3- + 3H2O}}}

Correspondingly, the solubility in an acidic medium decreases, whereby it increases again in a strongly hydrochloric acid medium, since arsenic (III) chloride AsCl _{3, which} is more soluble, is formed here .

With potassium hydroxide the arsenic acid forms potassium arsenite , with sodium hydroxide sodium arsenite . Copper (II) arsenite was previously used as a green pigment .

Individual evidence

↑ ^a ^b Entry on arsenic acid. In: Römpp Online . Georg Thieme Verlag, accessed on April 27, 2014.
↑ ^a ^b Entry on arsenic acid in the GESTIS substance database of the IFA , accessed on February 16, 2017(JavaScript required) .
↑ Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the specified labeling it falls under the group entry arsenic compounds, with the exception of those named in this appendix in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA) on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .

[roempp-1] Entry on arsenic acid. In: Römpp Online . Georg Thieme Verlag, accessed on April 27, 2014.

[GESTIS-2] Entry on arsenic acid in the GESTIS substance database of the IFA , accessed on February 16, 2017(JavaScript required) .

[CLP_100.240.769-3] Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the specified labeling it falls under the group entry arsenic compounds, with the exception of those named in this appendix in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA) on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .