Disodium hydrogen arsenate

Disodium hydrogen arsenate
Names
	IUPAC name Disodium hydrogen arsorate
	Other names Sodium arsenate dibasic
Identifiers
CAS Number	7778-43-0 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:91256 ;
ChemSpider	22908;
ECHA InfoCard	100.029.002
EC Number	231-902-4;
PubChem CID	24500;
UNII	ANU034TUJ4 ;
UN number	1685
CompTox Dashboard (EPA)	DTXSID8032047 ;
	InChI InChI=1S/AsH3O4.2Na/c2-1(3,4)5;;/h(H3,2,3,4,5);;/q;2*+1/p-2 Key: IHZDYHDJAVUIBH-UHFFFAOYSA-L;
	SMILES O[As](=O)([O-])[O-].[Na+].[Na+];
Properties
Chemical formula	H15Na2AsO11 (heptahydrate)
Molar mass	312.01 g/mol (heptahydrate)
Appearance	white solid
Solubility in water	good
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	poison
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H331, H350, H410
Precautionary statements	P201, P202, P261, P264, P270, P271, P273, P281, P301+P310, P304+P340, P308+P313, P311, P321, P330, P391, P403+P233, P405, P501
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Disodium hydrogen arsenate is the inorganic compound with the formula Na₂HAsO₄^.7H₂O. The compound consists of a salt and seven molecules of water of crystallization although for simplicity the formula usually omits the water component. The other sodium arsenates are NaH₂AsO₄ and Na₃AsO₄, the latter being called sodium arsenate. 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
₂AsO⁻
₄ + H₂O ⇌ HAsO²⁻
₄ + H₃O⁺ (pK_a2 = 6.94)

HAsO²⁻
₄ + H₂O ⇌ AsO³⁻
₄ + H₃O⁺ (pK_a3 = 11.5)

Related compounds

Monopotassium arsenate, KH₂AsO₄

References

^ Grund, S. C.; Hanusch, K.; Wolf, H. U. "Arsenic and Arsenic Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_113.pub2. ISBN 978-3-527-30673-2.

[Ullmann-1] Grund, S. C.; Hanusch, K.; Wolf, H. U. "Arsenic and Arsenic Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_113.pub2. ISBN 978-3-527-30673-2.

[1]