Question

Which of the following statement(s) is (are) correct with reference to the ferrous and ferric ions ?

• A. $Fe^{3+}$ gives brown colour with potassium ferricyanide
• B. $Fe^{2+}$ gives blue precipitate with potassium ferricyanide
• C. $Fe^{3+}$ gives red colour with potassium thiocyanate
• D. $Fe^{2+}$ gives brown colour with ammonium thiocyanate

Answer 1

Answer: (B), (C)

The blue precipitate of $Fe^{2+}$ ion with potassium ferricyanide is due to formation of Turnbull- blue $KFe[Fe(CN)_6].$
$ \, \, Fe^{2+} + K_3 [Fe (CN)_6] \longrightarrow \, KFe [Fe(CN)_6] + 2K^+$
The red colour of $Fe^{3+}$ ion with potassium thiocyanate is due to formation of $[Fe(SCN)_3].$
$ \, \, Fe^{3+} + 3KSCN \longrightarrow \, \underset {\text{Red coloured}}{[Fe (SCN)_3]} + 3K^+$