Silver selenate is an inorganic compound of silver and the selenate ion, with the chemical formula Ag2SeO4. It is a grey-white crystalline solid that is only slightly soluble in water.
Preparation Silver selenate can be prepared by reaction of silver carbonate with selenic acid:
Ag2CO3 + H2SeO4 → Ag2SeO4 + H2O + CO2↑
It can also be precipitated from aqueous solutions of a soluble silver salt and a soluble selenate. For example, silver nitrate and magnesium selenate have been used to prepare crystalline Ag2SeO4.
More recently, Ag2SeO4 has been synthesized hydrothermally from metallic silver and 40% selenic acid at 250 °C.
Structure and properties Silver selenate crystallizes in the orthorhombic crystal system and is isostructural with silver sulfate. Its space group is Fddd (No. 70), with eight formula units per unit cell.
At 25 °C, the lattice parameters are a = 10.388 Å, b = 12.981 Å and c = 6.0499 Å. The corresponding calculated density is 5.839 g/cm3.
The solubility of Ag2SeO4 in pure water at 25 °C is of the order of 10−3 mol kg−1. A thermodynamic review estimated a solubility range of approximately 1.2–2.4 × 10−3 mol kg−1 and a solubility product of about log Ksp = −8.26.
Silver selenate undergoes a reversible polymorphic transformation near 450 °C.
Modern thermal and spectroscopic studies have also characterized its decomposition behaviour, infrared spectrum and UV–visible absorption.
Complex formation Silver selenate dissolves in concentrated aqueous ammonia by formation of the linear diamminesilver(I) ion, [Ag(NH3)2]+. The corresponding crystalline selenate complex, [Ag(NH3)2]2SeO4, has been structurally characterized.
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