Arsenic pentasulfide is an
inorganic compound containing arsenic and sulfur.
Uses
Solids of the approximate formula
As2 S5 have been used as
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
s and chemical intermediates but are generally only of interest in academic laboratories.
Preparation
Arsenic pentasulfide is prepared by precipitation from an acidic solution of soluble As(V) salts by treatment with
hydrogen sulfide.
It may be also prepared by heating a mixture of arsenic and sulfur, extracting the fused mass with an
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
solution and reprecipitating arsenic pentasulfide at low temperature by addition of
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
.
Phosphorus pentasulfide
Phosphorus pentasulfide is the inorganic compound with the formula (monomer) or (dimer). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in carbon d ...
with the formula P
4S
10, is a molecular compound featuring tetrahedral phosphorus(V) centres. Trends in arsenic redox potentials suggest that As
2S
5 adopts a similar structure, a plausible alternative being an arsenic polysulfide.
Reactions
Arsenic pentasulfide hydrolyzes in boiling water, giving
arsenous acid
Arsenous acid (or arsenious acid) is the inorganic compound with the formula H3AsO3. It is known to occur in aqueous solutions, but it has not been isolated as a pure material, although this fact does not detract from the significance of As(OH)3.
...
and
sulfur:
: As
2S
5 + 6 H
2O → 2 H
3AsO
3 + 2 S + 3 H
2S
It oxidizes in air at elevated temperatures producing arsenic oxides, the products and yields of which are variable. In alkali metal sulfide solutions arsenic pentasulfide forms a
thioarsenate anion,
sS4sup>3−, which contain As(V) centres.
References
{{Arsenic compounds
Arsenic(V) compounds
Sulfides