Question

The complex [Fe(H${}_2$O)${}_5$NO]${}^{2+}$ is formed in the brown ring test for nitrates when freshly prepared FeSO${}_4$ solution is added to aqueous solution of ${N{O}_3}^{-}$ followed by addition of conc. H${}_2$SO${}_4$. Select correct statements about this complex :

• A. Color change is due to charge transfer.
• B. It has iron in +1 oxidation state and nitrosyl as NO${}^{+}$.
• C. It has magnetic moment of 3.87 B.M, confirming three unpaired electrons in Fe.
• D. In complex Fe has d${}^2$sp${}^3$ hybridization.

Answer 1

Answer: (A), (B), (C)

The correct options are
A Color change is due to charge transfer.
B It has iron in +1 oxidation state and nitrosyl as NO${}^{+}$.
C It has magnetic moment of 3.87 B.M, confirming three unpaired electrons in Fe.

(a) $F{e}^{2+}$ changes to brown-colored ring complex
(b) NO $\to N{O}^{+}+e^{-}$ $F{e}^{2+}+e^{-}\to F{e}^{+}$
$F{e}^{2+}\left[Ar\right]3d^6$
(c) $F{e}^{+}\left[Ar\right]3d^7$
Magnetic moment $\sqrt{n(n+2)}=\sqrt{15}=$ 3.87 BM
Thus, (a), (b), and (e) are true
(d) = $s{p}^3{d}^2$ hybridization.
Option D is false statement
Hence option A,B & C are correct.