Chemical Properties
Arsenic acid is a clear, white, semi-transparent crystal (sugar or sand-like) material.
Arsenic acid is one of the most commercially important pentavalent compounds of
arsenic. It is used for wood treatment/wood preservative, as a drying agent, a soil sterilant, and to make other arsenates. It is a broad-spectrum biocide, a fi nishing agent
for glass and metal, and a reagent in the retard of dyestuffs and organic arsenic compounds. Arsenic acid decomposes on heating, producing toxic and corrosive fumes. It
is a strong oxidant and reacts with combustible and reducing materials and attacks/
damages metals to produce toxic and flammable arsine. It is soluble in water and forms
the arsenate ion.
Uses
Pesticides; herbicides; fungicides; algicides.
Definition
Any salt or ester of arsenic acid. They are distributed widely in nature and contaminate coal and metal ores. Arsenates uncouple oxidative phosphorylation by replacing inorganic phosphorous in the ATP.
General Description
White crystals. Melting point 95°F. Excessive drying produces As2O5.5/3H2O.
Hazard
Carcinogen; toxic.
Reactivity Profile
ARSENIC ACID may evolve very toxic gaseous arsine (AsH3) from contact with active metals, such as zinc and aluminum [Inorganic Chemicals Handbook, I, p. 175]. When heated to decomposition, ARSENIC ACID, SOLID(7778-39-4) produces toxic fumes of metallic arsenic [Sax, 9th ed., p. 271]. The solution is weakly acidic and a weak oxidizing agent. Reacts with alkalis to generate some heat and precipitate arsenates.
Air & Water Reactions
Hygroscopic. Water soluble.
Health Hazard
Arsenic acid is absorbed into the body by inhalation of its vapor, through the skin, and
by ingestion. Arsenic acid is an eye irritant and may cause burns. Most injuries result
from exposure to dusts, causing conjunctivitis, lacrimation, photophobia, and chemosis.
Exposures to arsenic acid cause poisoning with symptoms of irritation of the eyes, the
skin, the respiratory tract, respiratory distress, sore throat, nausea, vomiting, diarrhea,
poor appetite, and stomach cramps. Arsenic acid also causes effects on the blood, cardiovascular system, gastrointestinal tract, liver, and peripheral nervous system, leading to polyneuropathy and convulsions. Repeated exposures to high concentrations of arsenic
acid have been reported to cause nerve damage, with “pins and needles,” numbness, and
weakness of the arms and legs, and even death. Tachycardia is frequently reported following ingestion of arsenic acid salts and is contributed to by anxiety, intravascular fl uid
depletion, and possibly direct arsenic-induced cardiotoxicity.
Health Hazard
Ingestion cuases irritation of stomach, weakness, other gastrointestinal symptoms. Overdose can cause arsenic poisoning, but symptoms are delayed.
Fire Hazard
Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated.
Physical properties
Hygroscopic translucent crystals; density between 2 to 2.5 g/cm3; melts at 35.5°C; loses water when heated to 160°C; highly soluble in cold water; soluble in alcohol, glycerol and alkalies.
Preparation
Arsenic acid is prepared by treating arsenic trioxide with concentrated nitric acid; or by combination of arsenic pentoxide with water. The latter reaction is very slow. It is also formed when meta- or pyroarsenic acid is treated with cold water.
