Weird Science

Preparation of Iron Oxalate

Polish ver­sion is here

Iron oxa­late is a salt for­med from oxa­lic acid and iron. Like most oxa­late com­po­unds, it is rela­ti­vely inso­lu­ble in water. Iron oxa­late is often used in a fasci­na­ting expe­ri­ment invo­lving spon­ta­ne­o­u­sly igni­ting iron pow­der (descri­bed here). You can buy this rea­gent from a che­mi­cal sup­ply store or syn­the­size it your­self easily. Natu­rally, today we're cho­o­sing the DIY appro­ach!

Requ­i­red Sub­stan­ces

To pre­pare iron oxa­late, you only need two sub­stan­ces:

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War­ning: As always, exer­cise cau­tion when wor­king with che­mi­cals. The rea­gents used in this expe­ri­ment may be irri­ta­ting or harm­ful. The author assu­mes no respon­si­bi­lity for any inju­ries or damage resul­ting from per­for­ming this expe­ri­ment. Pro­ceed at your own risk!

Oxa­lic acid, the sim­plest dicar­bo­xy­lic acid, appe­ars as a cry­stal­line pow­der in its dihy­drate form. Iron(II) sul­fate hep­ta­hy­drate forms gre­e­nish cry­stals.

The Syn­the­sis!

Once you have these two sub­stan­ces, you can start syn­the­si­zing iron oxa­late. First, pre­pare con­cen­tra­ted (or rela­ti­vely strong) solu­tions of oxa­lic acid and iron(II) sul­fate. Next, mix these solu­tions toge­ther. Hea­ting the mixture signi­fi­can­tly acce­le­ra­tes the reac­tion; the solu­tion quic­kly beco­mes clo­udy, and a yel­low iron oxa­late pre­ci­pi­tate begins to set­tle at the bot­tom. You can watch the reac­tion in this video:

Then, wash the pre­ci­pi­tate seve­ral times by decan­ta­tion, fil­ter it, and dry it tho­ro­u­ghly. Dry­ing sho­uld be car­ried out at room tem­pe­ra­ture (aro­und 20 °C [68 °F]) because higher tem­pe­ra­tu­res may cause decom­po­si­tion. The fini­shed iron oxa­late appe­ars as a light-yel­low pow­der:

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Expla­na­tion

Che­mi­cally, this is a sim­ple dou­ble-displa­ce­ment reac­tion. The net ionic equ­a­tion is shown below:

Ilustracja

The resul­ting iron oxa­late is prac­ti­cally inso­lu­ble in water and pre­ci­pi­ta­tes as a yel­low solid.

Have fun, and enjoy lear­ning some­thing new!

Fur­ther rea­dings:

Marek Ples

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