Thiocyanatoiron

Thiocyanatoiron

Names
IUPAC name pentaaquathiocyanatoiron(III)
Other names ferric thiocyanate iron(III) thiocyanate
Properties
Chemical formula	CFeH10NO5S
Molar mass	204.0048
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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 do 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)

Chemical properties

Acidity

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

Chemical reactions

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).

References

• Advanced Chemistry with Vernier, Lab Quest 10