Arsenic acid

Arsenic acid as such has not been isolated, but is only found in solution, where it is largely ionized.

[3] It is a tetrahedral species of idealized symmetry C3v with As–O bond lengths ranging from 1.66 to 1.71 Å.

[5] The resulting solution is cooled to give colourless crystals of the hemihydrate H3AsO4·0.5H2O (or 2H3AsO4·H2O), although the dihydrate H3AsO4·2H2O is produced when crystallisation occurs at lower temperatures.

[5] Arsenic acid is slowly formed when arsenic pentoxide is dissolved in water, and when meta- or pyroarsenic acid (H4As2O7) is treated with cold water.

It has found occasional use as a wood preservative, a broad-spectrum biocide, a finishing agent for glass and metal, and a reagent in the synthesis of some dyestuffs and organic arsenic compounds.

Structural formula
Ball-and-stick model
NFPA 704 four-colored diamond Health 4: Very short exposure could cause death or major residual injury. E.g. VX gas Flammability 0: Will not burn. E.g. water Instability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogen Special hazards (white): no code
Three bottles of arsenic acid from the Great Exhibition : impure, pure and distilled.