Question

Prussian blue colour is obtained by mixing together an aqueous solution of $F{e}^{3+}$ salt with:

• A. Ferricyanide
• B. Ferrocyanide
• C. Hydrogen cyanide
• D. Sodium cyanide

Answer 1

The correct option is B Ferrocyanide

Potassium ferricyanide reacts with ferrous iron in an acidic solution to produce the insoluble blue pigmnent, commonly referred to as Turnbull's blue. To detect ferric $\left(F{e}^{+3}\right)$ iron, potassium ferrocyanide is used instead of ferricyanide to get prussian blue.
$3\left[Fe\right(C{N}_6){]}^{4-}+4F{e}^{3+}+x{H}_{2}O\to F{e}_4[Fe(CN{)}_6{]}_3.x{H}_{2}O$
Hence the correct answer is option (b).