Question

When $ SCN^-$ is added to an aqueous solution containing $Fe(NO_3)_3$ ,the complex ion produced is

• A. $[Fe(OH_2 )_2 (SCN)] ^{2+}$
• B. $[Fe(OH_2 )_5 (SCN)]^{ 2+}$
• C. $[Fe(OH_2 )_8 (SCN)]^{2+}$
• D. $[Fe(OH_2) (SCN)]^{6+}$

Answer 1

Answer: (B)

On adding $SCN^− $ to an aqueous solution of $Fe(NO_3 )_ 3 $, a blood red colour, due to the formation of $[Fe(H_2O)_5 (SCN)]^{ 2+} $ complex, is obtained. This test is used for the detection of $Fe^{3+}$ ion.
$SCN^- + Fe(NO_3)_3 + H_2O \rightarrow \underset{\text{blood red colour}}{[Fe(OH _2)_5 (SCN)]^{2+}} + NO_3^-$