Pyrophoric Iron
 

A pyrophoric iron is prepared by pyrolysis of iron(II) oxalate. It can ignite spontaneously in contact with air.

Materials
Test tube (16 mm x 160 mm), small spoon, metal tray with sand, burner, metal stand with clamp.

Chemicals
Iron(II) oxalate
This salt can be prepared by mixing aqueous solutions of some soluble iron(II) salt, and oxalic acid, or sodium oxalate. The bright yellow precipitate should be filtered, dried at 180 ºC (to release its crystal water) and than used as precursor for pyrophoric iron.

Fig. 1. Apparatus

Fig. 2. Burning of Iron

Experimental

  • Add several small spoons of iron(II) oxalate in a test tube.
  • Assemble apparatus as it is shown on the Fig.1 in a fume hood.
  • Heat the test tube with a burner. Time after time rotate the test tube.
  • When the whole amount of the substance turns black stop the heating.
  • After cooling, in a fume hood, pour the content of the test tube on sand, in a metal tray as shown on Fig. 2.

Observation and Discussion

With mixing aqueous solution of iron(II) chloride and sodium oxalate a yellow precipitate of iron(II) oxalate dihydrate is obtained.
Fe2+(aq) + –OOCCOO–(aq) + 2H2O(l) = FeC2O4·2H2O(s)

By heating, black pyrophoric substance is obtained. In contact with air spontaneously ignites into iron(III) oxide.
Some of the reaction products can be seen in a tray with sand.   

Safety Tips
The experiment must be performed in a fume hood. The pyrolysis products are harmful and the burning of pyrophoric substance produces a smoke which should not be inhale.