Pyrophoric iron is a form of very fine iron powder that can spontaneously ignite and burn when coming into contact with air. However, room temperature is generally insufficient to trigger the spontaneous combustion of pyrophoric iron in air, a little bit of more heat is usually required.
Pyrophoric iron was produced through thermal decomposition of iron(II) oxalate (Fe(COO)2∙2H2O):
Fe(COO)2∙2H2O(s) → Fe(s) + 2CO2(g)+ 2H2O(g)
Upon heating, the yellow iron oxalate decomposed into black iron powder. The carbon dioxide (CO2) released in the course of the reaction creates an inert atmosphere which inhibits the oxidation of iron particles.
When the iron powder was poured out of the glass tube, it started to glow (ignited) in air and turned brown. This indicates the formation of iron(III) oxide (Fe2O3):
4Fe(s) + 3O2(g) → 2Fe2O3(s)
In pure oxygen atmosphere, the burning is more intensive. This was accomplished in two separate ways:
1) Pyrophoric iron was allowed to fall into the oxygen filled flask
2) Pure oxygen was blown into the pyrophoric iron filled test tube
Iron(II) oxalate can be prepared by mixing together the aqueous solutions of a soluble iron(II) salt (for example, iron(II) sulfate FeSO4∙7H2O) and a soluble oxalate (for example, potassium oxalate (COOK)2 ):
FeSO4(aq) + (COOK)2(aq) + 2H2O(l) → Fe(COO)2∙2H2O(s) + K2SO4(aq)
or in ionic form:
Fe2+(aq) + (COO)22-(aq) + 2H2O(l) → Fe(COO)2∙2H2O(s)
The formed precipitate must be filtered, washed with water and dried.
2) p,d-METALS: “Combustion of iron powder in air"