How is the conversion factor from orthophosphate (PO?) to phosphorus pentoxide (P2O5) determined?
Convert orthophosphate (PO₄) to phosphorus pentoxide (P2O5)
The Water Analysis Handbook and most other procedural publications have a conversion chart at the end of the phosphate procedure showing a conversion factor from orthophosphate (PO₄) to phosphorus pentoxide(P2O5) as 0.7473. This conversion is NOT based on the molecular weight of the two compounds. In solution phosphorus pentoxide converts to orthophosphate (and acid). The conversion of .75 is based on the rate of that reaction.