- Silver arsenate is an inorganic salt composed of silver(I) ions (Ag⁺) and the arsenate anion (AsO₄³⁻), in which arsenic is in its +5 oxidation state. The most common form is the tribasic salt Ag₃AsO₄, a sparingly soluble, brick-red to brownish solid that classically appears as a precipitate in qualitative inorganic analysis. Its distinctive color, combined with its low water solubility, makes silver arsenate a characteristic diagnostic compound for arsenate ions in solution. As with other silver(I) salts, prolonged exposure to light may cause slow surface darkening due to partial photoreduction of Ag⁺ to metallic silver. Because arsenate compounds are highly toxic and environmentally hazardous, silver arsenate is handled only in controlled laboratory conditions and is not used for routine applications.
- Structurally, silver arsenate is based on tetrahedral arsenate units (AsO₄³⁻), in which arsenic is surrounded symmetrically by four oxygen atoms. These tetrahedra behave as isolated anions, each carrying a −3 charge. Silver ions coordinate to oxygen atoms in these anions, forming an ionic lattice whose exact geometry can vary depending on crystallinity and hydration state. Silver ions, being soft and polarizable, often occupy irregular coordination environments with multiple Ag–O interactions at different distances rather than forming a single, well-defined geometry. This structural flexibility can give rise to slight distortions in the lattice, though the overall material remains an ionic solid dominated by electrostatic interactions between Ag⁺ and AsO₄³⁻.
- Chemically, silver arsenate is stable under ambient conditions but shows the typical reactivity pattern of both silver(I) salts and arsenate oxyanions. It is largely insoluble in water but can undergo dissolution or decomposition in strongly acidic or alkaline environments. In acidic media, the arsenate component is protonated to form species such as HAsO₄²⁻ or H₂AsO₄⁻, altering the compound’s stability. Similarly, in highly alkaline solutions, arsenate becomes highly soluble, forming tetrahydroxoarsenate species, leaving behind silver-containing residues. When strongly heated, silver arsenate may decompose to silver oxide (Ag₂O) or metallic silver and volatile or condensed arsenic oxides (depending on temperature). Because arsenate is a strong oxidizing oxyanion, the compound displays moderate oxidative behavior, although less pronounced than that of permanganates or chromates.
- In terms of uses, silver arsenate has no practical industrial, medical, or consumer applications due to the toxicity of arsenic(V) compounds and the expense of silver. However, it has historical and educational relevance in qualitative inorganic analysis, where formation of a red or brown Ag₃AsO₄ precipitate helps identify arsenate ions. In research contexts, silver arsenate occasionally appears in studies of arsenic speciation, environmental chemistry, or as a reference material for solubility product (Ksp) measurements. Outside these controlled settings, the compound is avoided due to toxicity and environmental persistence.
- Overall, silver arsenate is a niche but chemically interesting inorganic compound that illustrates the structural chemistry of arsenate tetrahedra and the typical behavior of low-solubility silver(I) salts. Although not of practical use, it remains relevant for understanding heavy-element oxyanion chemistry and the environmental geochemistry of arsenic.
