Sodium dihydrogen arsenate

Sodium dihydrogen arsenate
Names
	IUPAC name Sodium dihydrogen arsenate
	Other names sodium arsenate monobasic, sodium arsenate
Identifiers
CAS Number	10103-60-3 ;
PubChem CID	23677060;
CompTox Dashboard (EPA)	DTXSID8058611 ;
Properties
Chemical formula	NaH4AsO5 (monohydrate)
Molar mass	181.9 g/mol
Appearance	colourless solid
Density	2.53 g/cm3
Solubility in water	slightly soluble
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	toxic
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Sodium dihydrogen arsenate is the inorganic compound with the formula NaH₂AsO₄. Related salts are also called sodium arsenate, including Na₂HAsO₄ (disodium hydrogen arsenate) and NaH₂AsO₄ (sodium dihydrogen arsenate). Sodium dihydrogen arsenate is a colorless solid that is highly toxic.

The salt is the conjugate base of arsenic acid:

H₃AsO₄ ⇌ H₂AsO⁻
₄ + H⁺ (K₁ = 10^−2.19)

In the laboratory, it is prepared in this way, crystallizing from a hot saturated aqueous solution, where it is highly soluble when hot (75.3 g in 100 mL at 100 °C). It is obtained as the monohydrate.

Upon heating, solid NaH₂AsO₄H₂O, loses water of crystallization and converts to the pyroarsenate salt Na₂H₂As₂O₇.^[1]

References

^ P. W. Schenk "Arsenic, Antimony, Bismuth" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 602.

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[1] P. W. Schenk "Arsenic, Antimony, Bismuth" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 602.

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