Arsenous acid

Arsenous acid, also known as arsenious acid or arsenic(III) hydroxide, is a chemical compound. It is also an acid. Its chemical formula is As(OH)3. It has arsenic and hydroxide ions in it. The arsenic is in its +3 oxidation state.

Properties
Arsenous acid is a colorless solution. It is a weak acid. It reacts with bases to make arsenite salts. It is highly toxic. It cannot be made in a crystalline form because it turns into arsenic trioxide and water again. It is similar to phosphorous acid, although it is not a strong reducing agent.

Preparation
It is made by dissolving arsenic trioxide or arsenic trichloride in water. 

Hydrolysis of arsenic halides (such as arsenic trichloride) makes an chemical equilibrium containing some arsenous acid and hydrohalic acid, and some of the arsenic halide and water.

Related pages
Arsenic acid
Arsenic tribromide
Arsenic trisulfide
Nitrous acid

References

Category:Amphoteric hydroxides
Category:Arsenic compounds