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	23677060
Properties
Chemical formula	NaH4AsO5 (monohydrate)
Molar mass	181.9 g/mol
Appearance	colourless solid
Density	2.53 g/cm^3
Solubility in water	slightly soluble
Hazards
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

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.