Question

Which one of the following gives Prussian blue colour?

• A. $Fe _{2}\left[ Fe ( CN )_{6}\right]$
• B. $Na _{4}\left[ Fe ( CN )_{6}\right]$
• C. $Fe _{3}\left[ Fe ( CN )_{6}\right]_{3}$
• D. $Fe _{4}\left[ Fe ( CN )_{6}\right]_{3}$

Answer 1

Answer: (D)

Ferric salts (such as $FeCl _{3}$ ) form Prussian blue (blue ppt or colouration) with potassium ferrocyanide.

$4 FeCl _{3}+3 K _{4}\left[ Fe ( CN )_{6}\right] \longrightarrow \underset{\text{Prussian blue (ferric ferrocyanide)}}{Fe _{4}\left[ Fe ( CN )_{6}\right]_{3}}+12 KCl$