Sodium arsenate explained

Sodium arsenate is the inorganic compound with the formula Na₃AsO₄. Related salts are also called sodium arsenate, including Na₂HAsO₄ (disodium hydrogen arsenate) and NaH₂AsO₄ (sodium dihydrogen arsenate). The trisodium salt is a white or colourless solid that is highly toxic. It is usually handled as the dodecahydrate Na₃AsO₄^.12H₂O.

The compound can be obtained by neutralizing arsenic acid:

H₃AsO₄ + 3 NaOH → Na₃AsO₄ + 3 H₂OThe salt (as its dodecahydrate) is isomorphous with trisodium phosphate.^[1] The anion AsO₄^3- exists at high pH, but below pH 11.5, it converts to HAsO₄^2- (also written HOAsO₃^2-).

References

1. Remy, Francis; Guerin, Henri "Radiocrystallographic study of dodecahydrate trisodium arsenate and vanadate Na3AsO4.12H2O and Na3VO4.12H2O, and some hydrates of fluorinated or hydroxylated salts of general formula: M3XO4.xMY.(10 - x)H2O where M = Na, K; X = P, As, V and Y = F, OH" Bulletin de la Société Chimique de France 1970, vol. 6, pp. 2073-8.