Q. When $SCN^{-}$ is added to an aqueous solution containing $Fe\left( NO_{3} \right)_{3},$the complex ion produced is
A) $\left\lbrack Fe\left( OH_{2} \right)_{2}(SCN) \right\rbrack^{2 +}$
B) $\left\lbrack Fe\left( OH_{2} \right)_{5}(SCN) \right\rbrack^{2 +}$
C) $\left\lbrack Fe\left( OH_{2} \right)_{8}(SCN) \right\rbrack^{2 +}$
D) $\left\lbrack Fe\left( OH_{2} \right)(SCN) \right\rbrack^{6 +}$
Explanation
(b)
On adding $SCN^{-}$ to an aqueous solution of $Fe\left( NO_{3} \right)_{3}$, a blood red colour, due to formation of [$Fe\left( H_{2}O \right)_{5}(SCN\rbrack^{2 +}$complex is obtained. This test is used for the detection of $Fe^{3 +}$ion.
$SCN^{-} + Fe\left( NO_{3} \right)_{3} + {5H}_{2}O \rightarrow$
$\left\lbrack Fe\left( OH_{2} \right)_{5}(SCN) \right\rbrack^{2 +} + 3NO_{3}^{-}$
Blood red colour
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.