# How could I prepare Iron(III) arsenate (FeAsO4)?

I have no idea in which conditions this compound is formed and would like to find out any / different ways it can be prepared (any easy way not requiring expensive equipment would be great).

The monohydrate, $$\ce{FeAsO4.H2O}$$, is precipitated from solution. The salt, when dried in air, is a dull white insoluble substance, containing one molecule of water. When heated at 100° C. it becomes anhydrous. On treatment with sodium hydrogen carbonate solution, both the monohydrate and the anhydrous salt cause effervescence to take place, a soluble double arsenate being produced. It would appear, therefore, that the hydrated salt is acidic, and determinations of its basicity indicate that its formula is $$\ce{FeO.AsO2(OH)2}$$.