Disodium hydrogen arsenate

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.