Arsenous Acid
Definition and meaning of Arsenous Acid in chemistry.
Arsenous acid is a weak inorganic acid formed from the hydration of arsenic trioxide, containing arsenic in the +3 oxidation state. It readily forms arsenite salts in reaction with bases and exists in equilibrium with its anhydrous form in solution.
In more detail
Arsenous acid (H3AsO3) is much weaker than arsenic acid (H3AsO4), with pKa values around 9.2 and 12.1 for its successive ionizations. The compound acts as a Lewis acid and has historically been used in wood preservation, pesticide manufacturing, and semiconductor processing, though such applications are increasingly restricted. Arsenic compounds are highly toxic because they interfere with cellular metabolism and respiration at very low concentrations, making arsenous acid and its salts significant environmental and health concerns.
Key facts
| Chemical Formula | H3AsO3 |
|---|---|
| Arsenic Oxidation State | +3 |
| Acid Strength | Weak acid; pKa ~9.2, ~12.1 |
| Field | Inorganic Chemistry |
When arsenic trioxide dissolves in water and is neutralized with sodium hydroxide solution, it forms sodium arsenite (Na3AsO3), a white crystalline solid commonly used as a herbicide.
Frequently asked questions
How does arsenous acid differ from arsenic acid?
Arsenous acid contains arsenic in the +3 oxidation state and is much weaker than arsenic acid (H3AsO4), which has arsenic in the +5 state and is substantially stronger.
Why are arsenous acid compounds so toxic?
Arsenic compounds interfere with cellular respiration and enzyme function by binding to sulfhydryl groups in proteins, causing damage at very low exposure levels.