Arsenic acid is the
chemical compound with the
formula H
3AsO
4. More descriptively written as AsO(OH)
3, this colorless
acid is the
arsenic analogue of
phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but only found in solution where it is largely ionized. Its
hemihydrate form (H
3AsO
4·½H
2O) does form stable crystals. Crystalline samples dehydrate with condensation at 100 °C.