Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Thiocyanatoiron (systematically named thiocyanatoiron(2+)) is a inorganic cation with the chemical formula [Fe(SCN)]2+. It is known to produce a blood red color in solution. This is used as a test for Fe3+ in the laboratory. Fe3+ reacts with thiocyanate to give a series of intensely red colored compounds which remain in the solution and does not undergo any reaction after the formation of the stable octahedral structure. In high concentration of SCN− the compound is fairly octahedral with six thiocyanate ligands bonded to iron atom. Thiocyanatoiron forms a pentahydrate.
Thiocyanatoiron must be stored in an acidic solution to prevent the formation of FeOH2+ ions. The excess H+ ions in the acidic solution prevent Fe3+ from engaging in side reactions. Thiocyanatoiron decomposes with exposure to light. The thiocyanatoiron ion is usually formed through an equilibrium reaction:
- Fe3+(aq) + SCN−(aq) ↔ [Fe(SCN)]2+(aq)
The iron(III) segment in thiocyanatoiron(III)s such as thiocyanatoiron can assimilate a hydroxide into the molecule by substitution:
- FeSCN2+ + OH− → FeOH2+ + SCN−
Because of this capture of a hydroxide (OH−), thiocyanatoiron has Arrhenius acidic character. In aqueous solution, most thiocyanatoiron is hydrolyzed.
- FeSCN2+ + H2O FeOH2+ + HSCN
Thiocyanatoiron undergoes the typical chemical reactions of a thiocyanatoiron(III). Upon treatment with a standard base, it converts to dihydroxyiron(III) or trihydroxyiron(III), and metal thiocyanate. Reduction of thiocyanatoiron(III) gives thiocyanatoiron(II).
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- Advanced Chemistry with Vernier, Lab Quest 10