Most common oxidation states: +3, +5

Characteristics: Gray, very brittle substance; sublimes at 615^o. Combines readily with sulfur and oxygen at high temperatures.

 Characteristic reactions of As³⁺:

In slightly acid solution, yellow As₂S₃ forms on addition of H₂S:

2As³⁺(aq) + 3H₂S(aq) <==> As₂S₃(s) + 6H⁺(aq)

Hydrogen sulfide causes no precipitation from neutral or alkaline solutions. The precipitate is soluble in concentrated HNO₃ or in ammoniacal H₂O₂:

As₂S₃(s) + 8H⁺(aq) + 2NO₃^-(aq) <==> 2As³⁺(aq) + 3S(s) + 2NO(g) + 4H₂O(l)

As₂S₃(s) + 14H₂O₂(aq) + 12NH₃(aq) <==> 2AsO₄^3-(aq) + 3SO₄^2-(aq) + 8H₂O(l) + 12NH₄⁺(aq)

The precipitate is insoluble in dilute, nonoxidizing acids such as HCl.

 Silver Ion:

Silver ion will precipitate yellow silver arsenite from neutral or slightly basic solution:

3Ag⁺(aq) + AsO₃^3-(aq) <==> Ag₃AsO₃(s)

It is insoluble in water, but soluble in aqueous ammonia and in acids.

Oxidizing agents readily oxidize arsenites (+3) to arsenates (+5) in alkaline or neutral solutions:

2Cu(OH)₂(s) + AsO₃^3-(aq) <==> Cu₂O(s) (red) + AsO₄^3-(aq) + 2H₂O(l) 

Cl^-, SO₄^2-, NH₃(aq), OH^-

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