The rusting of iron is a spotaneous exothermic process. When iron is in the form of a super fine powder, enough heat is generated to ignite the mixture when it is exposed to air. In this form, iron is deemed pyrphoric. In this experiment, I will make pyrophoric iron by decomposing iron(II) oxalate. Iron(II) oxalate will be made by mixing solutions of oxalic acid and iron(II) sulfate.
H2C2O4 + FeSO4 --> H2SO4 + FeC2O4
The iron(II) oxalate will then be heated to give carbon dioxide and metallic iron. Some iron oxide and hydroxides are also formed.
FeC2O4 --> Fe + 2CO2
Other pyrophoric metals such as copper and lead can be produced in an analgous matter.
The starting materials for this experiment were both purchased over the counter although they also can be made from potentially more available starting components. Oxalic acid is sold as "Wood Bleach" for bleaching decks and iron sulfate is sold as a gardening micronutrient. Among other ways, oxalic acid can be synthesized by oxidizing surcrose with concentrated nitric acid. The most straightforward of many routes to iron sulfate is to dissolve iron in sulfuric acid.
Finely divided powdered metals can be useful in some chemical preparations. Often times, the oxalate salt can be included in a mixture and then heated to produce the metal in situ. This metal can, for instance, either participate in a thermite reaction or serve as a catalyst.
5.0g of oxalic acid and 11.0g of ferrous sulfate were each dissolved in 50mL of water and heated until the solutes completely dissolved. The two solutions were then mixed together and immediately a yellow precipitate of ferrous oxalate formed. The precipitate was washed extensively with tap water to rid of formed sulfuric acid.
I let the solution stand for a while before filtering it and letting the precipitate dry for 20 hours. Then, I took about half of the yield and heated it with an alcohol flame in a test tube. The salt slowly turned into the black powder of iron which was confirmed by attraction to a magnet. When I poured out the contents of the test tube, the powder sparked and embered and quickly transformed into a brown powder of iron oxide.
