chem report question:

it's SCN(-), the thiocyanate-N or isothiocyanate. note that it's the N which bounds to iron(III) ion.

iron(III) is a hard lewis acid due to its high charge density. the nitrogen on thiocyanate has small size, thus having high charge density and is a hard lewis base.
(comparatively, the sulfur atom is soft due to large size and lower charge density, thus is soft lewis base)

thiocyanate is often used to test the presence of iron(III) ion, by forming characteristic red complex ion, [Fe(NCS)(OH2)5] (2+) , pentaaqua(thiocyanato-N)iron(III) ion.


or you can think in this way.
- iron(III) chloride solid dissolves in water to give [Fe(OH2)6] (3+), the aqua complex instead of the chloro-complex. water is thus stronger than chloride ion.
- after addition of thiocyanate, it reacts immediately with the aqua-ion to give the red complex. thus thiocyanate-N is stronger than the aqua-ligand.


2010-12-14 02:28:30 補充：
alright.
iron(II) oxalate / iron(II) ethanedioate.
(NH4)2Fe(SO4)2.6H2O + H2C2O4 ------> FeC2O4 + (NH4)2SO4 + H2SO4 + 6H2O
or just ionic eq.:
Fe(2+) + (COOH)2 ------> FeC2O4 + 2H(+)


also, note that the final product has a pair of non-superimposable images. they're chiral compounds!