Silver phosphate or silver orthophosphate is a light sensitive, yellow, water insoluble chemical compound composed of silver and phosphate ions of formula Ag3PO4.
Synthesis, reactions and properties
Silver phosphate is formed as a yellow precipitate by the reaction between a soluble silver compound, such as silver nitrate with a soluble orthophosphate; its solubility product is 8.89×10âˆ'17 mol4dmâˆ'12. The precipitation reaction is analytically significant and can be used to in qualitatively or quantitative tests for phosphates.
This compound is dissolved by nitric acid, or by ammonia. It can also be formed as large crystals by gradual loss of ammonia from an ammoniacal solution of silver phosphate; the reaction can be used in quantitative analysis of phosphate ions. Depending on the method of preparation different crystal forms of silver phosphate can be produced of the same lattice structure.
Uses
As well as being important in analytical chemistry, the precipitation of silver phosphate is also used in silver staining of biological materials (after reduction to silver metal) - as a magnifying agent for phosphate.
Silver phosphate also found use in early photography as a light sensitive agent.
In 2010, silver phosphate was reported as having a high (90%) quantum yield as a photocatalyst for the visible light photochemical splitting of water, and for production of activated oxygen by the same method.
Silver phosphate is also a potential material for incorporating silver ion antibacterial properties into materials.
Other silver phosphates
Silver pyrophosphate Ag4P2O7 (CAS No. 13465-97-9) can be prepared as a white precipitate from reaction of silver(I) and pyrophosphate ions. Like silver orthophosphate it is light sensitive. Silver orthophosphate turns red on exposure to light. It has a density of 5.306g/cm3 and a melting point of 585 °C. A hydrate also exists which decomposes at 110 °C.
Silver metaphosphate (AgPO3) (CAS No. 13465-96-8) is a white solid with a density of 6.370g/cm3 and a melting point of 482 °C. A hydrate also exists which decomposes at 240 °C.
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