Silver phosphate Formula
Silver phosphate, also known argentous phosphate or silver orthophosphate, is an inorganic salt used as stained or light sensitive substance for revealing in photography.
Formula and structure: The silver phosphate chemical formula is Ag3PO4 and the molar mass is 418.574 g mol-1. This salt is formed by three silver cations (Ag+) and one phosphate anion (PO43-) which forms a cubic crystal structure. Its chemical structure can be written as below, in the common representations used for organic molecules.
Occurrence: Silver phosphate cannot be found in nature. It is prepared as described below.
Preparation: Silver phosphate is formed as a yellow precipitate when it is reacted silver nitrate and the salt orthophosphate. The product obtained is not soluble in water, thus it can be filtered and recovery as a pure solid.
AgNO3 + PO43- → Ag3PO4(S)
Physical properties: Silver phosphate is a yellow solid which become darker when impure. It is not soluble in water and its density is 6.37 g mL-1. It is moderately soluble in acid or solutions. Silver phosphate melting point is 849 °C. It is light sensitive.
Chemical properties: The ion phosphate at high temperature can suffer a reaction of condensation to form pyrophosphate, in these conditions it is also possible to form silver pyrophosphate when silver nitrate is added. This second phosphate is also sensitive to the light and this chemical characteristics made them a good candidates for getting new material with photocatalytic activity.
Uses: Silver phosphate is used as a standard for determining the concentration of phosphates in solution. Moreover, it can be used as a staining of biological materials. Due to silver phosphate is a light sensitive agent; it is used in photography as emulsions. It is also used as catalysts on some reactions and for medical purposes as astringent, bactericide, etc.
Health effects / safety hazards: Silver phosphate can cause respiratory disease and coughing. It also causes skin and eyes irritation and serious damage in eyes.