Question

Aqueous solution of $FeS{O}_4$ gives tests for both $F{e}^{2+}$ and $S{O}_4^{2-}$ but after addition of excess of KCN, solution ceases to give test for $F{e}^{2+}$. This is due to the formation of :

• A. the double salt $FeS{O}_4.2KCN.6H_{2}O$
• B. $Fe{\left(CN\right)}_3$
• C. the complex ion ${\left[Fe{\left(CN\right)}_6\right]}^{4-}$
• D. the complex ion ${\left[Fe{\left(CN\right)}_6\right]}^{3-}$

Answer 1

The correct option is C the complex ion ${\left[Fe{\left(CN\right)}_6\right]}^{4-}$

As $F{e}^{+2}$ ion test ceases in excess of KCN, means this form complex in presence of excess KCN. Reaction of process: $F{e}^{+2}\stackrel{KCN}{\to }\left[Fe\right(CN{)}_6{]}^4$.